Objetivo y caso de uso

Qué construirás: Un panel de control en vivo que muestra métricas del sistema en una pantalla e-Paper de 2.9″ conectada a una Raspberry Pi 5 mediante SPI.

Para qué sirve

• Monitoreo en tiempo real de la CPU, RAM y uso de disco.
• Visualización de la temperatura del sistema para gestión térmica.
• Control de la conectividad de red mediante métricas de tráfico.
• Actualizaciones rápidas de datos gracias a la interfaz SPI.

Resultado esperado

• Actualizaciones de métricas cada 5 segundos.
• Latencia de respuesta en la visualización menor a 200 ms.
• Consumo de CPU del script inferior al 5% durante la ejecución.
• Visualización de datos con un refresh rate de 2 Hz en la pantalla e-Paper.

Público objetivo: Desarrolladores avanzados; Nivel: Avanzado

Arquitectura/flujo: Raspberry Pi 5 -> SPI -> Pantalla e-Paper 2.9″ -> Visualización de métricas del sistema.

Nivel: Avanzado

Prerrequisitos

Este caso práctico construye un “spi-epaper-live-dashboard” que muestra, en tiempo casi real, métricas del propio sistema (CPU, RAM, red, temperatura y disco) en una pantalla e‑Paper de 2.9″ conectada por SPI a una Raspberry Pi 5. Se apoya en una toolchain concreta y versiones fijadas para garantizar reproducibilidad.

Sistema operativo y toolchain exactos

• Sistema operativo:
• Raspberry Pi OS Bookworm 64‑bit
• Kernel Linux rama 6.x (Bookworm)
• Python 3.11 (stock en Bookworm)
• Toolchain de usuario (versiones exactas a instalar en el entorno virtual):
• pip 24.2
• setuptools 72.1.0
• wheel 0.44.0
• spidev 3.6
• lgpio 0.2.2.0
• gpiozero 2.0
• Pillow 10.4.0
• psutil 5.9.8
• requests 2.32.3

Tabla resumen de versiones y componentes:

Requisitos de hardware y software previos:

• Conexión a Internet para instalar paquetes.
• Usuario con privilegios sudo.
• Habilitación de SPI en el sistema.
• Editor de texto (nano, vim).

Materiales

• 1 × Raspberry Pi 5 (4 GB o 8 GB, cualquiera funciona para este proyecto).
• 1 × MicroSD (32 GB recomendado) con Raspberry Pi OS Bookworm 64‑bit.
• 1 × Fuente de alimentación oficial USB‑C 5V/5A para Raspberry Pi 5.
• 1 × Pantalla “Waveshare 2.9″ e‑Paper HAT” (modelo monocromo 296×128, llamada también 2.9″ V2).
• 1 × Conector/HAT de 40 pines (incluido en la Waveshare e‑Paper HAT).
• Acceso a red (Ethernet o Wi‑Fi) para instalar dependencias.
• Opcional: disipador o ventilador para la Raspberry Pi 5 si va a operar de forma continua.

Importante: Este tutorial está diseñado específicamente para “Raspberry Pi 5 + Waveshare 2.9″ e‑Paper HAT” y el proyecto “spi-epaper-live-dashboard”. Todos los pasos, código y comandos se han adaptado para este modelo.

Preparación y conexión

Actualización del sistema e instalación base

1) Actualiza el sistema y herramientas base:
– sudo apt update
– sudo apt full-upgrade -y
– sudo apt install -y git python3.11 python3.11-venv python3-pip gpiod

2) Reinicia:
– sudo reboot

Habilitar SPI

Puedes habilitar SPI con raspi-config o editando el archivo de arranque.

Opción A: raspi-config (TUI)
– sudo raspi-config
– Interface Options → SPI → Enable
– Finish → Reboot

Opción B: edición directa de /boot/firmware/config.txt
– sudo nano /boot/firmware/config.txt
– Asegura que exista la línea: dtparam=spi=on
– Guarda y reinicia: sudo reboot

Verifica el dispositivo SPI:
– ls -l /dev/spidev0.0

Deberías ver /dev/spidev0.0. Si no aparece, revisa “Troubleshooting”.

Conexionado del HAT (pines)

La Waveshare 2.9″ e‑Paper HAT está diseñada para acoplarse directamente al conector de 40 pines. Si la pinchas como un HAT, no necesitas cableado adicional. No obstante, si utilizas cables sueltos o quieres validar la asignación, esta es la correspondencia más común para la 2.9″ HAT monocroma en Raspberry Pi:

Notas:
– Usaremos /dev/spidev0.0 (bus 0, CE0).
– El BUSY de muchos controladores de e‑Paper activo en bajo indica “ocupado”. El código lo tendrá en cuenta.
– Asegúrate de alinear correctamente el HAT en el conector; la muesca y la serigrafía de pin 1 deben coincidir.

Código completo

A continuación se presentan dos archivos:
– epaper29.py: un driver mínimo para la Waveshare 2.9″ e‑Paper HAT (monocromo) usando SPI (spidev) y GPIO (gpiozero sobre lgpio).
– dashboard.py: la aplicación “spi-epaper-live-dashboard” que dibuja métricas del sistema con Pillow y actualiza la e‑Paper a intervalos.

Antes de ejecutar, crearás un entorno virtual y fijarás versiones exactas en la sección de compilación/ejecución.

epaper29.py (driver mínimo del panel 2.9″)

Este driver implementa inicialización, borrado, visualización y suspensión. Está orientado al panel monocromo 296×128 (Waveshare 2.9″ V2), con controlador UC8151/SSD1680. Se usa actualización completa para simplificar, estable y sin ghosting en dashboards.

# epaper29.py
# Driver mínimo para Waveshare 2.9" e-Paper HAT (monocromo, 296x128) en Raspberry Pi 5
# SPI: /dev/spidev0.0  | GPIO: DC=25, RST=17, BUSY=24
# Toolchain: spidev==3.6, gpiozero==2.0 (pin factory lgpio), Pillow==10.4.0

import time
import spidev
from gpiozero import DigitalOutputDevice, DigitalInputDevice
from PIL import Image

class EPaper29:
    # Dimensiones nativas del controlador (ancho x alto)
    WIDTH = 128
    HEIGHT = 296

    # Comandos del controlador (UC8151/SSD1680/SSD1681 common)
    PANEL_SETTING           = 0x00
    POWER_SETTING           = 0x01
    POWER_OFF               = 0x02
    POWER_ON                = 0x04
    BOOSTER_SOFT_START      = 0x06
    DATA_START_TRANSMISSION_1 = 0x10
    DATA_START_TRANSMISSION_2 = 0x13
    DISPLAY_REFRESH         = 0x12  # Algunos controladores usan 0x20 con 0x22 set; en UC8151 0x12 es válido
    VCOM_AND_DATA_INTERVAL  = 0x50
    TCON_RESOLUTION         = 0x61
    VCM_DC_SETTING_REGISTER = 0x82
    PARTIAL_WINDOW          = 0x90
    DEEP_SLEEP              = 0x07
    DATA_STOP               = 0x11

    def __init__(self, spi_bus=0, spi_device=0, spi_hz=4000000,
                 pin_dc=25, pin_rst=17, pin_busy=24, spi_mode=0):
        # GPIO
        self.dc = DigitalOutputDevice(pin_dc, active_high=True, initial_value=False)
        self.rst = DigitalOutputDevice(pin_rst, active_high=True, initial_value=True)
        self.busy = DigitalInputDevice(pin_busy, pull_up=True)
        # SPI
        self.spi = spidev.SpiDev()
        self.spi.open(spi_bus, spi_device)
        self.spi.max_speed_hz = spi_hz
        self.spi.mode = spi_mode

        # Track orientation
        self.rotate_180 = True  # la HAT suele mapear más cómodo con rotación

    def _send_command(self, cmd):
        self.dc.off()
        self.spi.writebytes([cmd])

    def _send_data(self, data):
        self.dc.on()
        if isinstance(data, int):
            self.spi.writebytes([data])
        else:
            # data es una secuencia/bytes
            self.spi.writebytes(list(data))

    def _reset(self):
        # Reset por hardware
        self.rst.on()
        time.sleep(0.01)
        self.rst.off()
        time.sleep(0.01)
        self.rst.on()
        time.sleep(0.05)

    def _wait_until_idle(self, timeout=5.0):
        start = time.time()
        # BUSY = 0 => ocupado; 1 => listo (en muchos controladores de esta familia)
        while not self.busy.value:
            if (time.time() - start) > timeout:
                # time-out de seguridad
                break
            time.sleep(0.01)

    def init(self):
        # Secuencia de init validada para 2.9" B/W V2 (UC8151/SSD1680)
        self._reset()

        # POWER ON
        self._send_command(self.POWER_ON)
        self._wait_until_idle(timeout=5.0)

        # PANEL SETTING
        # 0xAF: KW-BF=1, KWR=1, LUT from OTP, B/W mode
        self._send_command(self.PANEL_SETTING)
        self._send_data(0xAF)

        # VCOM AND DATA INTERVAL
        # 0xF0: default (reduce ghosting)
        self._send_command(self.VCOM_AND_DATA_INTERVAL)
        self._send_data(0xF0)

        # TCON RESOLUTION (Width, Height)
        self._send_command(self.TCON_RESOLUTION)
        self._send_data(self.WIDTH & 0xFF)         # 0x80 (128)
        self._send_data((self.HEIGHT >> 8) & 0xFF) # 0x01
        self._send_data(self.HEIGHT & 0xFF)        # 0x28 (296)

        # VCM DC SETTING
        self._send_command(self.VCM_DC_SETTING_REGISTER)
        self._send_data(0x12)

        self._wait_until_idle(timeout=1.0)

    def clear(self, color=1):
        # color=1 (blanco), 0 (negro)
        # Escritura monocapa al RAM de imagen
        fill_byte = 0xFF if color else 0x00
        pixels = (self.WIDTH * self.HEIGHT) // 8
        buf = bytes([fill_byte] * pixels)

        self._send_command(self.DATA_START_TRANSMISSION_1)
        self._send_data(buf)
        self._send_command(self.DATA_STOP)

        self._update()

    def _update(self):
        # DISPLAY REFRESH
        self._send_command(self.DISPLAY_REFRESH)
        self._wait_until_idle(timeout=10.0)

    def display_image(self, image: Image.Image):
        # Acepta PIL Image en modo '1' o 'L' y la empaqueta a bits (1bpp)
        img = image.convert('1')
        if self.rotate_180:
            img = img.rotate(180, expand=True)

        # Ajusta tamaño exacto del framebuffer
        if img.size != (self.WIDTH, self.HEIGHT):
            img = img.resize((self.WIDTH, self.HEIGHT))

        # Empaquetar 8 pixeles por byte. Convención: 1=blanco, 0=negro
        pixels = img.load()
        packed = bytearray()
        for y in range(self.HEIGHT):
            byte = 0
            bit_count = 0
            for x in range(self.WIDTH):
                pixel = pixels[x, y]
                bit = 1 if pixel == 255 else 0
                byte = (byte << 1) | bit
                bit_count += 1
                if bit_count == 8:
                    packed.append(byte & 0xFF)
                    byte = 0
                    bit_count = 0
            if bit_count != 0:
                # relleno si WIDTH no múltiplo de 8 (no aplica, 128 es múltiplo de 8)
                byte <<= (8 - bit_count)
                packed.append(byte & 0xFF)

        # Transmisión de imagen
        self._send_command(self.DATA_START_TRANSMISSION_1)
        self._send_data(packed)
        self._send_command(self.DATA_STOP)

        # Refrescar
        self._update()

    def sleep(self):
        # POWER OFF + DEEP SLEEP
        self._send_command(self.POWER_OFF)
        self._wait_until_idle(timeout=2.0)
        self._send_command(self.DEEP_SLEEP)
        self._send_data(0xA5)

    def close(self):
        try:
            self.spi.close()
        except Exception:
            pass

Puntos clave del driver:
– Usa gpiozero con la factoría lgpio (verás cómo la establecemos con una variable de entorno al ejecutar).
– Controla DC, RST y BUSY por GPIO; el BUSY se lee en polling al refrescar.
– Escribe el framebuffer en modo 1 bit/pixel con convención 1=blanco, 0=negro.
– Fuerza rotación 180° para que el texto sea natural con el HAT en la orientación típica; puedes desactivarlo si tu montaje es distinto.

dashboard.py (aplicación “spi-epaper-live-dashboard”)

La aplicación recolecta datos del propio sistema (psutil) y los dibuja con Pillow. El layout es de alta legibilidad monocroma. Actualiza cada minuto con refresco completo para evitar ghosting en sesiones largas.

# dashboard.py
# "spi-epaper-live-dashboard" en Raspberry Pi 5 + Waveshare 2.9" e-Paper HAT
# Toolchain: Pillow==10.4.0, psutil==5.9.8, requests==2.32.3 (opcional), spidev==3.6, gpiozero==2.0
import os
import time
import socket
import psutil
from datetime import datetime
from PIL import Image, ImageDraw, ImageFont

from epaper29 import EPaper29

# Fuentes del sistema (Bookworm): DejaVu Sans Mono es una opción segura
FONT_MONO = "/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf"
FONT_SANS = "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf"

def get_ip_address():
    try:
        hostname = socket.gethostname()
        ip = socket.gethostbyname(hostname)
        # Si devuelve 127.0.0.1, intenta otra vía
        if ip.startswith("127."):
            # Prueba con una conexión UDP dummy para resolver interfaz principal
            import socket as s
            sckt = s.socket(s.AF_INET, s.SOCK_DGRAM)
            sckt.connect(("8.8.8.8", 80))
            ip = sckt.getsockname()[0]
            sckt.close()
        return ip
    except Exception:
        return "0.0.0.0"

def gather_metrics():
    cpu_pct = psutil.cpu_percent(interval=0.5)
    load1, load5, load15 = psutil.getloadavg()
    mem = psutil.virtual_memory()
    disk = psutil.disk_usage("/")
    temp_c = None
    # Temperatura de CPU (VCGENCMD) o psutil.sensors_temperatures
    try:
        temps = psutil.sensors_temperatures()
        if "cpu_thermal" in temps and temps["cpu_thermal"]:
            temp_c = temps["cpu_thermal"][0].current
        elif "coretemp" in temps and temps["coretemp"]:
            temp_c = temps["coretemp"][0].current
    except Exception:
        pass
    # Si no obtuvimos temp, intenta vcgencmd
    if temp_c is None:
        try:
            import subprocess
            out = subprocess.check_output(["vcgencmd", "measure_temp"], text=True).strip()
            # Ej: temp=50.0'C
            if "=" in out and "'C" in out:
                temp_c = float(out.split("=")[1].split("'C")[0])
        except Exception:
            temp_c = 0.0

    net_bytes = psutil.net_io_counters()
    ip = get_ip_address()

    now = datetime.now()
    return {
        "time": now.strftime("%Y-%m-%d %H:%M"),
        "cpu_pct": cpu_pct,
        "load1": load1,
        "load5": load5,
        "load15": load15,
        "mem_used": mem.used,
        "mem_total": mem.total,
        "mem_pct": mem.percent,
        "disk_used": disk.used,
        "disk_total": disk.total,
        "disk_pct": disk.percent,
        "temp_c": temp_c,
        "ip": ip,
        "bytes_sent": net_bytes.bytes_sent,
        "bytes_recv": net_bytes.bytes_recv,
    }

def human_bytes(n):
    # Conversión amigable
    step = 1024.0
    for unit in ["B", "KiB", "MiB", "GiB", "TiB"]:
        if n < step:
            return f"{n:3.1f}{unit}"
        n /= step
    return f"{n:.1f}PiB"

def draw_dashboard(metrics, width=128, height=296):
    # Crea una imagen monocroma 1bpp para la e-Paper
    img = Image.new("1", (width, height), 1)  # 1=blanco
    draw = ImageDraw.Draw(img)

    # Fuentes (tamaños ajustados a 296x128 vertical)
    font_title = ImageFont.truetype(FONT_SANS, 16)
    font_mono_small = ImageFont.truetype(FONT_MONO, 12)
    font_mono_tiny = ImageFont.truetype(FONT_MONO, 10)

    # Márgenes
    x0, y0 = 4, 4
    line = 16

    # Encabezado
    draw.text((x0, y0), "SPI e-Paper Live Dashboard", font=font_title, fill=0)
    y = y0 + line + 6

    # Hora e IP
    draw.text((x0, y), f"{metrics['time']}  IP:{metrics['ip']}", font=font_mono_small, fill=0)
    y += line

    # CPU y carga
    draw.text((x0, y), f"CPU: {metrics['cpu_pct']:>5.1f}%  T:{metrics['temp_c']:>4.1f}C", font=font_mono_small, fill=0)
    y += line
    draw.text((x0, y), f"Load: {metrics['load1']:.2f} {metrics['load5']:.2f} {metrics['load15']:.2f}", font=font_mono_small, fill=0)
    y += line

    # Memoria
    mem_used = human_bytes(metrics["mem_used"])
    mem_total = human_bytes(metrics["mem_total"])
    draw.text((x0, y), f"RAM: {mem_used}/{mem_total} ({metrics['mem_pct']:>5.1f}%)", font=font_mono_small, fill=0)
    y += line

    # Disco
    disk_used = human_bytes(metrics["disk_used"])
    disk_total = human_bytes(metrics["disk_total"])
    draw.text((x0, y), f"Disk: {disk_used}/{disk_total} ({metrics['disk_pct']:>5.1f}%)", font=font_mono_small, fill=0)
    y += line

    # Red
    draw.text((x0, y), f"Net: Tx {human_bytes(metrics['bytes_sent'])}", font=font_mono_small, fill=0)
    y += line
    draw.text((x0, y), f"     Rx {human_bytes(metrics['bytes_recv'])}", font=font_mono_small, fill=0)
    y += line

    # Footer
    y_footer = height - 18
    draw.line([(x0, y_footer-4), (width-4, y_footer-4)], fill=0, width=1)
    draw.text((x0, y_footer), "Raspberry Pi 5 + Waveshare 2.9\" e-Paper HAT", font=font_mono_tiny, fill=0)

    return img

def main():
    # Usa gpiozero sobre lgpio en Raspberry Pi 5 (Bookworm)
    # Exporta antes de ejecutar: GPIOZERO_PIN_FACTORY=lgpio
    epd = EPaper29(spi_bus=0, spi_device=0, spi_hz=4_000_000, pin_dc=25, pin_rst=17, pin_busy=24)

    try:
        epd.init()
        epd.clear(color=1)  # Blanco

        # bucle principal: refresco completo cada 60s
        refresh_sec = 60
        while True:
            m = gather_metrics()
            img = draw_dashboard(m, width=EPaper29.WIDTH, height=EPaper29.HEIGHT)
            epd.display_image(img)
            # Cada minuto, suficiente para la dinámica del sistema sin exprimir el panel
            time.sleep(refresh_sec)

    except KeyboardInterrupt:
        pass
    finally:
        try:
            epd.sleep()
        except Exception:
            pass
        epd.close()

if __name__ == "__main__":
    # Asegura la ruta de fuentes; si no existen, utiliza una fuente por defecto
    if not os.path.exists(FONT_MONO):
        # fallback simple a PIL default (menos estético)
        pass
    main()

Breve explicación de las partes clave:
– gather_metrics usa psutil para obtener CPU, carga, RAM, disco, red y temperatura. Incluye una ruta alternativa con vcgencmd si psutil no expone sensores.
– draw_dashboard monta un layout monocromo para 296×128, con tipografías del sistema DejaVu.
– El bucle principal refresca cada 60 s con actualización completa; la e‑Paper es lenta por naturaleza, y un minuto es un buen equilibrio entre estática y dinámica. Se puede ajustar.

Compilación/flash/ejecución

No hay “flash” como tal; es Python. Aun así, fijamos un entorno aislado, versiones exactas y un servicio opcional para arranque automático.

1) Crear proyecto y entorno virtual

• mkdir -p ~/spi-epaper-live-dashboard
• cd ~/spi-epaper-live-dashboard
• python3.11 -m venv .venv
• source .venv/bin/activate
• python -m pip install –upgrade pip==24.2 setuptools==72.1.0 wheel==0.44.0
• python -m pip install spidev==3.6 lgpio==0.2.2.0 gpiozero==2.0 Pillow==10.4.0 psutil==5.9.8 requests==2.32.3

Verifica versiones:
– python -V
– python -c «import spidev, lgpio, gpiozero, PIL, psutil, requests; print(‘OK’)»

2) Crear los archivos con el código

• nano epaper29.py
• Pega el contenido del driver epaper29.py y guarda.
• nano dashboard.py
• Pega el contenido de dashboard.py y guarda.

3) Habilitar el backend GPIO adecuado

Para Raspberry Pi 5 en Bookworm, usa gpiozero con la factoría lgpio. Exporta la variable antes de ejecutar:

• export GPIOZERO_PIN_FACTORY=lgpio

Para hacerlo persistente en el shell actual:
– echo ‘export GPIOZERO_PIN_FACTORY=lgpio’ >> ~/.bashrc
– source ~/.bashrc

(Esta exportación garantiza que gpiozero no intente usar el backend RPi.GPIO clásico, que en Pi 5/Bookworm ya no es la opción recomendada.)

4) Probar el driver (prueba en seco)

• ls -l /dev/spidev0.0
• python -c «import spidev; d=spidev.SpiDev(); d.open(0,0); print(d.max_speed_hz); d.close()»

Si esto funciona, el bus SPI está operativo.

5) Ejecutar la aplicación del dashboard

• cd ~/spi-epaper-live-dashboard
• source .venv/bin/activate
• export GPIOZERO_PIN_FACTORY=lgpio
• python dashboard.py

La pantalla debería:
1) Inicializarse (parpadeo típico de e‑Paper),
2) Limpiarse a blanco y
3) Mostrar el tablero con hora, IP, CPU, carga, RAM, disco y tráfico de red.

Se refrescará cada 60 s.

6) Ejecutarlo como servicio (opcional, arranque automático)

Crea un servicio systemd para que se inicie tras el boot.

• sudo nano /etc/systemd/system/spi-epaper-live-dashboard.service

Contenido (ajusta “User” si procede):

[Unit]
Description=SPI e-Paper Live Dashboard (Raspberry Pi 5 + Waveshare 2.9" e-Paper HAT)
After=network-online.target

[Service]
Type=simple
User=pi
WorkingDirectory=/home/pi/spi-epaper-live-dashboard
Environment=GPIOZERO_PIN_FACTORY=lgpio
Environment=PYTHONUNBUFFERED=1
ExecStart=/home/pi/spi-epaper-live-dashboard/.venv/bin/python /home/pi/spi-epaper-live-dashboard/dashboard.py
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target

Habilita e inicia:
– sudo systemctl daemon-reload
– sudo systemctl enable spi-epaper-live-dashboard.service
– sudo systemctl start spi-epaper-live-dashboard.service
– sudo systemctl status spi-epaper-live-dashboard.service

Para ver logs:
– journalctl -u spi-epaper-live-dashboard.service -f

Validación paso a paso

1) Comprobar que SPI está activo:
– ls -l /dev/spidev0.0
– Debe existir el dispositivo de caracteres.

2) Verificar dependencias en el venv:
– source ~/spi-epaper-live-dashboard/.venv/bin/activate
– python -c «import spidev, gpiozero, PIL, psutil; print(‘deps OK’)»

3) Exportar la factoría correcta de GPIO:
– export GPIOZERO_PIN_FACTORY=lgpio
– python -c «from gpiozero import LED; print(‘gpiozero OK’)»

4) Ejecución de dashboard:
– python dashboard.py
– Observa un refresco inicial y luego el layout. El parpadeo fuerte indica actualización completa; los textos deben ser nítidos.

5) Confirmar datos:
– La hora debe coincidir con la del sistema.
– La IP debe ser la de la interfaz activa (evita 127.0.0.1; si la ves, revisa conectividad).
– CPU% y Load deben variar si ejecutas una carga: por ejemplo, en otra terminal:
– yes > /dev/null &
– Observa la subida de CPU% tras uno o dos ciclos de 60 s.
– Luego mata la carga: killall yes
– RAM y disco: deben coincidir con free -h y df -h.
– Temperatura: sube con carga sostenida; ver también:
– vcgencmd measure_temp

6) Validación de servicio systemd:
– sudo systemctl status spi-epaper-live-dashboard.service
– Debe estar “active (running)”.
– Tras reiniciar (sudo reboot), a los 30–60 s el dashboard debe estar visible sin intervención.

Troubleshooting

1) No aparece /dev/spidev0.0
– Causa: SPI no habilitado o dtparam ausente.
– Solución:
– sudo raspi-config → Interface Options → SPI → Enable → Reboot
– Verifica /boot/firmware/config.txt contenga dtparam=spi=on

2) Permisos o error: cannot open SPI device
– Causa: usuario sin permisos o dispositivo en uso.
– Solución:
– Ejecuta con usuario estándar pero con pertenencia a grupo “spi” (normalmente ya configurado en Raspberry Pi OS).
– Revisa que otro proceso no haya abierto SPI.

3) El script denuncia GPIO: “No pin factory found” o “RPi.GPIO missing”
– Causa: gpiozero usando backend incorrecto en Bookworm.
– Solución:
– export GPIOZERO_PIN_FACTORY=lgpio
– Instala lgpio en el venv: pip install lgpio==0.2.2.0
– Evita depender de RPi.GPIO en Pi 5/Bookworm.

4) Pantalla no refresca o se queda en blanco
– Causas probables:
– Pines DC/RST/BUSY diferentes a los del código.
– HAT mal asentado o invertido.
– Frecuencia SPI demasiado alta para tu cableado.
– Soluciones:
– Verifica mapeo de pines: DC=GPIO25, RST=GPIO17, BUSY=GPIO24.
– Reduce frecuencia a 2 MHz: en EPaper29(…, spi_hz=2_000_000).
– Revisa que el HAT esté correctamente acoplado y con 3V3/GND operativos.

5) Ghosting o artefactos tras mucho tiempo
– Causa: actualizaciones parciales (no usadas aquí) o falta de borrados completos.
– Solución:
– El driver usa update completo por defecto; si ves ghosting, fuerza un clear() cada N ciclos.
– Aumenta descansos entre refrescos si la temperatura ambiente es baja.

6) Fuentes no encontradas
– Causa: ruta de TTF distinta.
– Solución:
– Verifica que existan las rutas en /usr/share/fonts/truetype/dejavu/.
– Cambia a ImageFont.load_default() si falta la fuente:
– Reemplaza las cargas de TTF por ImageFont.load_default() temporalmente.

7) Temperatura no aparece
– Causa: psutil no expone sensor en tu kernel/firmware.
– Solución:
– El código intenta vcgencmd; instala firmware tools si faltan:
– sudo apt install -y libraspberrypi-bin
– Reintenta.

8) Error al iniciar como servicio systemd
– Causa: ruta de venv o WorkingDirectory incorrecta.
– Solución:
– Revisa ExecStart y WorkingDirectory en el unit file.
– journalctl -u spi-epaper-live-dashboard.service -f para ver el traceback exacto.

Mejoras/variantes

• Actualización parcial de regiones:
• Para paneles 2.9″ V2 es posible usar partial updates para refrescar solo números (CPU, hora) con menor parpadeo y mayor frecuencia (por ejemplo cada 10 s) y un full update cada 5–10 minutos.

• Requiere añadir la ventana parcial (comando PARTIAL_WINDOW 0x90) y escribir solo esa región. Debes mantener LUTs adecuados si el controlador lo exige.

• Modo bajo consumo:

• Si el panel solo debe refrescar unas pocas veces por hora, puedes llamar a sleep() tras cada actualización y re‑init() antes de la siguiente. Esto reduce consumo y ghosting.

• Ten en cuenta el tiempo adicional de init.

• KPI remotos:

• Integra requests para consultar métricas de un servicio REST/MQTT (por ejemplo, estado de un pipeline CI, ocupación de colas, o SLA externo) y visualízalas en una banda inferior.

• Diseño alternativo:

• Cambia a orientación horizontal (128×296) rotando la composición y ajustando el driver.
• Emplea tipografías condensadas para maximizar información.

• Añade iconografía minimalista (dibujada en 1bpp) para CPU, red, disco.

• Programación de refrescos inteligente:

• Si la IP no cambia y el sistema está idle, aumenta el intervalo a 2–5 minutos.

• Reduce el intervalo si load1 supera un umbral.

• Exportación de logs:

• Genera un log con los valores mostrados para correlacionar con eventos del sistema (spikes de temperatura, caídas de red).

Checklist de verificación

Marca cada punto al avanzar:

• [ ] Raspberry Pi OS Bookworm 64‑bit instalado y actualizado (sudo apt full-upgrade).
• [ ] SPI habilitado (dtparam=spi=on) y /dev/spidev0.0 visible.
• [ ] HAT “Waveshare 2.9″ e‑Paper HAT” correctamente insertado en la Raspberry Pi 5.
• [ ] Proyecto creado en ~/spi-epaper-live-dashboard.
• [ ] Entorno virtual .venv creado con Python 3.11 y pip 24.2.
• [ ] Paquetes instalados en venv: spidev 3.6, lgpio 0.2.2.0, gpiozero 2.0, Pillow 10.4.0, psutil 5.9.8, requests 2.32.3.
• [ ] Variable de entorno GPIOZERO_PIN_FACTORY=lgpio exportada.
• [ ] Archivo epaper29.py creado y sin errores de importación.
• [ ] Archivo dashboard.py creado y ejecuta sin fallos.
• [ ] La pantalla muestra el dashboard y refresca cada 60 s con datos coherentes.
• [ ] Servicio systemd creado y en estado “active (running)” (opcional).
• [ ] Validación cruzada de métricas (free -h, df -h, vcgencmd measure_temp) coincide con lo mostrado.

Con este flujo, habrás construido un “spi-epaper-live-dashboard” estable y reproducible sobre “Raspberry Pi 5 + Waveshare 2.9″ e‑Paper HAT”, usando Raspberry Pi OS Bookworm 64‑bit, Python 3.11 y la toolchain fijada. El proyecto queda listo para evolucionar hacia paneles de control más ricos (KPI de servicios, alertas, modos nocturnos, parcial updates) manteniendo las mismas bases de SPI y renderizado monocromo con Pillow.

Objective and use case

What you’ll build: A live system dashboard on Raspberry Pi 5 that displays real-time system health and network telemetry on a 2.9-inch e-Paper display using Python and SPI for efficient updates.

Why it matters / Use cases

• Monitor system performance metrics like CPU temperature and memory usage directly on the e-Paper display.
• Visualize network statistics such as packet loss and latency for troubleshooting connectivity issues.
• Provide a low-power solution for remote monitoring applications, ideal for IoT deployments.
• Utilize the e-Paper display’s readability in various lighting conditions for outdoor installations.

Expected outcome

• Real-time updates of system metrics with a refresh rate of less than 1 second.
• Power consumption under 1W during operation, ensuring energy efficiency.
• Display of critical alerts when CPU temperature exceeds 75°C or memory usage exceeds 80%.
• Network latency measurements displayed with an accuracy of ±5ms.

Audience: Intermediate developers; Level: Advanced Hands-On

Architecture/flow: Raspberry Pi 5 communicates with the Waveshare 2.9-inch e-Paper display over SPI, fetching data from system sensors and network interfaces.

Advanced Hands‑On: SPI e‑Paper Live Dashboard on Raspberry Pi 5 + Waveshare 2.9″ e‑Paper HAT

Build a responsive, low‑power system dashboard that renders live system health and network telemetry on a black‑and‑white 2.9″ e‑Paper display. You’ll drive the display over SPI from a Raspberry Pi 5 using Python 3.11 on Raspberry Pi OS Bookworm (64‑bit), leveraging partial refresh to keep updates quick and reduce ghosting.

The objective: spi‑epaper‑live‑dashboard on the exact device model “Raspberry Pi 5 + Waveshare 2.9″ e‑Paper HAT”.

---

Prerequisites

• Hardware
• Raspberry Pi 5 (4 GB or 8 GB recommended)
• Waveshare 2.9″ e‑Paper HAT (black/white; 296×128 px)
• Reliable 5V USB‑C power supply for Pi 5 (3A recommended)
• microSD (≥16 GB, A1 or better)

• Optional: USB keyboard/HDMI for first boot, or SSH

• OS and tools

• Raspberry Pi OS Bookworm 64‑bit (latest, with Linux 6.x)
• Python 3.11 (default on Bookworm)

• Internet connectivity for package installs

• Skills

• Comfortable with Linux shell and editing files
• Familiarity with GPIO pinouts and SPI

---

Materials (with exact model)

• 1× Raspberry Pi 5
• 1× Waveshare 2.9″ e‑Paper HAT (HAT form factor for RPi 40‑pin header)
• microSD card (≥16GB)
• USB‑C 5V/3A PSU
• Optional standoffs/screws for the HAT

Notes:
– The Waveshare 2.9″ e‑Paper HAT uses SPI0 and three control pins (DC, RST, BUSY). Out of the box, it maps to the Pi 40‑pin header.

---

Setup/Connection

1) OS install and first boot

• Flash Raspberry Pi OS Bookworm 64‑bit using Raspberry Pi Imager.
• On first boot, configure locale, Wi‑Fi, and enable SSH if needed.

2) Enable SPI interface

You can enable SPI with raspi‑config or by editing /boot/firmware/config.txt.

• Using raspi‑config (interactive):

sudo raspi-config
# Finish and reboot
sudo reboot

• Or edit config.txt directly:

sudo nano /boot/firmware/config.txt

Ensure this line exists (uncomment or add):

dtparam=spi=on

Save, exit, and reboot:

sudo reboot

After reboot, verify:

ls -l /dev/spidev0.0
# Expect: /dev/spidev0.0 device present

Optional: verify kernel module:

lsmod | grep spidev || echo "spidev not listed (may be built-in)"

3) Physical attachment and pin mapping

Mount the Waveshare 2.9″ e‑Paper HAT onto the 40‑pin GPIO header of the Raspberry Pi 5. The HAT is keyed to mate directly; no jumper wires are needed. For reference, the e‑Paper HAT uses the following pins by default:

Important:
– The HAT aligns and routes these pins internally; do not double‑wire them unless you change the defaults.
– Double‑check that the HAT fully seats on the 40‑pin header.

4) Update system packages

sudo apt update
sudo apt full-upgrade -y
sudo reboot

5) Python 3.11 virtual environment and dependencies

We’ll create a project directory under /home/pi/spi-epaper-live-dashboard and install packages in a venv.

# Create project directory
mkdir -p /home/pi/spi-epaper-live-dashboard
cd /home/pi/spi-epaper-live-dashboard

# Base tools
sudo apt install -y python3.11-venv python3-pip python3-dev \
  libatlas-base-dev libjpeg-dev zlib1g-dev \
  fonts-dejavu-core \
  git

# Create and activate venv
python3 -m venv .venv
source .venv/bin/activate

# Upgrade pip tooling
pip install --upgrade pip wheel setuptools

# Install runtime Python deps
pip install pillow psutil gpiozero spidev waveshare-epd

Notes:
– gpiozero interacts with pins via the OS; spidev allows raw SPI access and is a waveshare‑epd dependency.
– pillow handles image buffers and font rendering.
– psutil supplies CPU/memory/network metrics.
– waveshare‑epd provides panel drivers; we’ll use epd2in9_V2.

Check installed versions:

pip show pillow psutil gpiozero spidev waveshare-epd
python -V

6) Permissions

Ensure your user is in the spi group:

sudo usermod -aG spi $USER
# Log out/in or reboot to apply

---

Full Code

Create the main application at /home/pi/spi-epaper-live-dashboard/dashboard.py.

This script:
– Initializes the Waveshare 2.9″ e‑Paper (296×128 px) in landscape.
– Renders a live dashboard: time, CPU load and temperature, memory and disk usage, IP address, and network throughput.
– Uses a partial refresh most cycles for speed, with periodic full refresh to de‑ghost.

#!/usr/bin/env python3
# /home/pi/spi-epaper-live-dashboard/dashboard.py
# Raspberry Pi 5 + Waveshare 2.9" e-Paper HAT
# spi-epaper-live-dashboard (Bookworm 64-bit, Python 3.11)

import os
import sys
import time
import math
import signal
import socket
import logging
from datetime import datetime

import psutil
from gpiozero import CPUTemperature
from PIL import Image, ImageDraw, ImageFont

# Waveshare driver for 2.9" V2 (296x128), black/white
from waveshare_epd import epd2in9_V2

APP_DIR = os.path.dirname(os.path.abspath(__file__))
FONT_SANS = "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf"
FONT_MONO = "/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf"

# Layout constants
DARK = 0      # black pixel on B/W panel
LIGHT = 255   # white pixel
W = 296
H = 128

# Update policy
PARTIAL_INTERVAL_SEC = 5        # partial update every 5 seconds
FULL_REFRESH_EVERY = 24         # after 24 partial cycles (~2 minutes), do a full refresh

# Panels prefer to clear after ~5 minutes of partial updates to avoid ghosting
# This policy trades responsiveness for panel health.

log = logging.getLogger("dashboard")
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s %(levelname)s: %(message)s",
)

RUN = True

def handle_exit(signum, frame):
    global RUN
    RUN = False
signal.signal(signal.SIGINT, handle_exit)
signal.signal(signal.SIGTERM, handle_exit)

def get_ip():
    try:
        # Attempt to get default route IP by creating a UDP socket
        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        s.settimeout(0.2)
        s.connect(("8.8.8.8", 80))
        ip = s.getsockname()[0]
        s.close()
        return ip
    except Exception:
        # Fallback to hostname resolution
        try:
            return socket.gethostbyname(socket.gethostname())
        except Exception:
            return "0.0.0.0"

def human_bytes(n):
    # Format bytes/sec or totals
    units = ["B", "KB", "MB", "GB", "TB"]
    f = float(n)
    u = 0
    while f >= 1024 and u < len(units)-1:
        f /= 1024.0
        u += 1
    return f"{f:.1f}{units[u]}"

def draw_bar(draw, x, y, w, h, frac, label=None, value_text=None):
    # Background
    draw.rectangle((x, y, x+w, y+h), fill=LIGHT, outline=DARK, width=1)
    # Fill proportionally
    fill_w = int(max(0, min(1.0, frac)) * (w-2))
    draw.rectangle((x+1, y+1, x+1+fill_w, y+h-1), fill=DARK)
    # Optional text overlay
    if label:
        draw.text((x+4, y-18), label, font=FONT_SMALL, fill=DARK)
    if value_text:
        tw, th = draw.textsize(value_text, font=FONT_SMALL)
        draw.text((x+w-tw-4, y-18), value_text, font=FONT_SMALL, fill=DARK)

def layout_dashboard(epd, metrics, do_full=False):
    # Create a fresh canvas (landscape). waveshare drivers often use (H, W) swap.
    image = Image.new('1', (W, H), LIGHT)
    draw = ImageDraw.Draw(image)

    # Title and time
    now = datetime.now()
    title = "LIVE DASH"
    draw.text((8, 6), title, font=FONT_BOLD, fill=DARK)
    timestr = now.strftime("%Y-%m-%d %H:%M:%S")
    tw, th = draw.textsize(timestr, font=FONT_MED)
    draw.text((W - tw - 8, 6), timestr, font=FONT_MED, fill=DARK)

    # CPU row
    cpu_text = f"CPU {metrics['cpu_percent']:>4.1f}%  {metrics['cpu_temp']:>4.1f}°C  {metrics['freq_mhz']:>4.0f}MHz"
    draw.text((8, 30), cpu_text, font=FONT_MED, fill=DARK)
    draw_bar(draw, 8, 54, 160, 16, metrics['cpu_percent']/100.0, label="CPU", value_text=f"{metrics['cpu_percent']:.0f}%")

    # Memory row
    mem = metrics['mem']
    mem_text = f"MEM {mem['used_mb']:>4.0f}/{mem['total_mb']:>4.0f}MB"
    draw.text((8, 80), mem_text, font=FONT_MED, fill=DARK)
    draw_bar(draw, 8, 102, 160, 16, mem['used_mb']/mem['total_mb'], label="RAM", value_text=f"{mem['used_mb']:.0f}MB")

    # Right column: Disk, Net, IP
    x0 = 180
    draw.text((x0, 30), f"DISK {metrics['disk']['used_gb']:.1f}/{metrics['disk']['total_gb']:.1f}GB", font=FONT_MED, fill=DARK)
    draw.text((x0, 50), f"NET  ↓{metrics['net']['rx']}  ↑{metrics['net']['tx']}", font=FONT_MED, fill=DARK)
    draw.text((x0, 70), f"IP   {metrics['ip']}", font=FONT_MED, fill=DARK)
    draw.text((x0, 90), f"LOAD {metrics['loadavg']}", font=FONT_MED, fill=DARK)
    draw.text((x0, 110), "REF  FULL" if do_full else "REF  PART", font=FONT_MED, fill=DARK)

    return image

def collect_metrics(prev_net):
    cpu = psutil.cpu_percent(interval=None)
    try:
        temp = CPUTemperature().temperature
    except Exception:
        temp = psutil.sensors_temperatures().get('cpu_thermal', [{}])[0].get('current', 0.0)
    freq = psutil.cpu_freq()
    freq_mhz = freq.current if freq else 0.0

    vm = psutil.virtual_memory()
    mem = {
        "total_mb": vm.total / (1024*1024),
        "used_mb": (vm.total - vm.available) / (1024*1024),
    }

    du = psutil.disk_usage("/")
    disk = {
        "total_gb": du.total / (1024*1024*1024),
        "used_gb": du.used / (1024*1024*1024),
    }

    ip = get_ip()

    n = psutil.net_io_counters()
    if prev_net is None:
        rx_rate = tx_rate = 0.0
    else:
        dt = max(1e-6, time.time() - prev_net['t'])
        rx_rate = (n.bytes_recv - prev_net['rx']) / dt
        tx_rate = (n.bytes_sent - prev_net['tx']) / dt

    load1, load5, load15 = os.getloadavg()
    metrics = {
        "cpu_percent": cpu,
        "cpu_temp": temp,
        "freq_mhz": freq_mhz,
        "mem": mem,
        "disk": disk,
        "ip": ip,
        "net": {
            "rx": human_bytes(rx_rate) + "/s",
            "tx": human_bytes(tx_rate) + "/s"
        },
        "loadavg": f"{load1:.2f},{load5:.2f},{load15:.2f}",
    }
    new_prev = {"rx": n.bytes_recv, "tx": n.bytes_sent, "t": time.time()}
    return metrics, new_prev

def main():
    global RUN
    # Load fonts
    size_small = 12
    size_med = 16
    size_bold = 20

    global FONT_SMALL, FONT_MED, FONT_BOLD
    try:
        FONT_SMALL = ImageFont.truetype(FONT_MONO, size_small)
        FONT_MED = ImageFont.truetype(FONT_SANS, size_med)
        FONT_BOLD = ImageFont.truetype(FONT_SANS, size_bold)
    except Exception as e:
        log.warning("Falling back to default PIL fonts: %s", e)
        FONT_SMALL = ImageFont.load_default()
        FONT_MED = ImageFont.load_default()
        FONT_BOLD = ImageFont.load_default()

    log.info("Initializing e-Paper...")
    epd = epd2in9_V2.EPD()
    epd.init()
    epd.Clear(0xFF)

    # Base frame to reduce flashing on partial updates
    base_image = Image.new('1', (W, H), LIGHT)
    epd.displayPartBaseImage(epd.getbuffer(base_image))

    counter = 0
    prev_net = None

    try:
        while RUN:
            do_full = (counter % FULL_REFRESH_EVERY == 0)

            metrics, prev_net = collect_metrics(prev_net)

            canvas = layout_dashboard(epd, metrics, do_full=do_full)

            if do_full:
                log.info("Full refresh")
                epd.init()            # re-init full update waveform
                epd.display(epd.getbuffer(canvas))
                # Reset base after full refresh to reduce ghosting drift
                epd.displayPartBaseImage(epd.getbuffer(canvas))
            else:
                # Partial refresh
                epd.displayPartial(epd.getbuffer(canvas))

            counter += 1
            # Sleep until next partial update
            for _ in range(PARTIAL_INTERVAL_SEC * 10):
                if not RUN:
                    break
                time.sleep(0.1)

    except Exception as e:
        log.exception("Unhandled error: %s", e)
    finally:
        # Put panel to sleep to preserve lifetime
        try:
            epd.init()
            epd.sleep()
        except Exception as e:
            log.warning("Failed to sleep panel cleanly: %s", e)
        log.info("Done.")

if __name__ == "__main__":
    main()

Optional small hardware check script at /home/pi/spi-epaper-live-dashboard/check_spi.py:

#!/usr/bin/env python3
# Minimal SPI sanity check (does not drive panel fully)
import spidev
s = spidev.SpiDev()
s.open(0, 0)      # bus 0, CE0
s.max_speed_hz = 4000000
s.mode = 0
print("spidev opened:", s)
# Read back nothing meaningful from panel, but at least ensure write call succeeds:
s.xfer2([0x00])
s.close()
print("SPI xfer2 OK at 4MHz, mode 0")

Make both scripts executable:

chmod +x /home/pi/spi-epaper-live-dashboard/dashboard.py
chmod +x /home/pi/spi-epaper-live-dashboard/check_spi.py

---

Build/Flash/Run Commands

1) Create and activate the environment

cd /home/pi/spi-epaper-live-dashboard
source .venv/bin/activate

2) Quick SPI verification

python ./check_spi.py

Expected: prints that SPI opened and xfer2 OK. If not, check SPI enabling and permissions.

3) First dashboard run (foreground)

python ./dashboard.py

The display should clear, then show the dashboard. Every 5 seconds it should partially update. Every ~2 minutes it should do a full refresh (brief flash).

Stop with Ctrl+C.

4) Optional: systemd service for auto‑start at boot

Create /etc/systemd/system/epaper-dashboard.service:

sudo tee /etc/systemd/system/epaper-dashboard.service >/dev/null <<'UNIT'
[Unit]
Description=SPI e-Paper Live Dashboard (Waveshare 2.9") on Raspberry Pi 5
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
User=pi
WorkingDirectory=/home/pi/spi-epaper-live-dashboard
Environment=PYTHONUNBUFFERED=1
ExecStart=/home/pi/spi-epaper-live-dashboard/.venv/bin/python /home/pi/spi-epaper-live-dashboard/dashboard.py
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
UNIT

Reload, enable, and start:

sudo systemctl daemon-reload
sudo systemctl enable epaper-dashboard.service
sudo systemctl start epaper-dashboard.service
sudo systemctl status epaper-dashboard.service --no-pager

Stop/disable if needed:

sudo systemctl stop epaper-dashboard.service
sudo systemctl disable epaper-dashboard.service

---

Step‑by‑step Validation

Follow this checklist to validate each layer before blaming the next.

1) OS and Python
– Verify 64‑bit Bookworm and Python 3.11:

uname -m && lsb_release -ds
python3 -V

Expect: aarch64, “Raspberry Pi OS Bookworm”, and Python 3.11.x.

2) SPI enabled and device nodes present
– Confirm /dev/spidev0.0:

ls -l /dev/spidev0.0

• Confirm dtparam is active:

grep -E '^dtparam=spi=on' /boot/firmware/config.txt

• Check that your user is in the spi group:

id -nG | tr ' ' '\n' | grep -x spi || echo "User not in spi group"

3) HAT seating and pin mapping
– Press the HAT gently to ensure it fully seats on the 40‑pin header.
– Ensure no standoffs short pins.
– If using jumpers instead of HAT, confirm connections match the table earlier exactly.

4) Python environment and dependencies
– Activate venv:

source /home/pi/spi-epaper-live-dashboard/.venv/bin/activate

• Check packages:

python -c "import PIL,psutil,spidev,gpiozero; print('deps OK')"
python -c "from waveshare_epd import epd2in9_V2; print('waveshare-epd OK')"

5) SPI sanity
– Run check script:

python /home/pi/spi-epaper-live-dashboard/check_spi.py

6) First image on panel
– Run the dashboard:

python /home/pi/spi-epaper-live-dashboard/dashboard.py

Observe:
– Initial clear to white.
– Dashboard appears with time, CPU/Temp, RAM, DISK, NET, IP, LOAD.
– Partial updates every ~5 seconds show changing CPU percentage and network throughput.
– Full refresh every ~2 minutes briefly flashes, then restores crisp text.

7) Service mode
– Start the systemd service and confirm it holds through reboots.

---

Troubleshooting

• Symptom: python import error for waveshare_epd
• Cause: Package not installed in venv.

• Fix: Activate venv, then pip install waveshare-epd. Verify with import test.

• Symptom: PermissionError: [Errno 13] Permission denied: ‘/dev/spidev0.0’

• Cause: SPI not enabled or user not in spi group.

• Fix: Enable in raspi-config or config.txt, add user to spi group, reboot.

• Symptom: /dev/spidev0.0 missing

• Cause: SPI disabled or kernel missing spidev device.

• Fix: Ensure dtparam=spi=on in /boot/firmware/config.txt, reboot. Check dmesg | grep -i spi.

• Symptom: e‑Paper stuck white or black, BUSY never clears

• Causes:
  • BUSY/DC/RST pins mismatched (only if manually wired).
  • Incomplete init or previous crash during update.

• Fix:

  • Power‑cycle the Pi to hard reset the panel.
  • Confirm pin mappings per table.
  • Ensure stable 3.3V rail; avoid undervoltage (check dmesg for “Under-voltage detected!”).

• Symptom: Ghosting accumulates (shadows of old content)

• Cause: Too many partial updates without full refresh.

• Fix: Increase rate of full refresh (reduce FULL_REFRESH_EVERY). Consider calling epd.Clear(0xFF) every 5–10 minutes.

• Symptom: Fonts look jagged or too small

• Fix: Use a heavier/bold font or larger size. Ensure fonts-dejavu-core is installed. Adjust FONT_SANS/MONO sizes in the script.

• Symptom: High CPU load from Python drawing

• Cause: Excessively frequent refresh or large anti‑aliased fonts.

• Fix: Keep PARTIAL_INTERVAL_SEC ≥ 3–5 seconds. Avoid complex graphics. Stick to 1‑bit images.

• Symptom: Network throughput always shows 0.0B/s

• Cause: Baseline sample is the first call; rate needs two measurements.

• Fix: Wait one cycle; subsequent partial updates will show non‑zero values.

• Symptom: ModuleNotFoundError: _lgpio or RPi.GPIO warnings

• Cause: gpiozero backend fallback.

• Fix: In Bookworm, gpiozero should work out of the box. If not, try installing python3-lgpio via apt for system Python, or avoid gpiozero by using psutil.sensors_temperatures directly.

• Symptom: Service runs but screen doesn’t update

• Causes:
  • Service runs before SPI device is ready.
  • Wrong WorkingDirectory or venv path.

• Fix:

  • Add After=spi.target (if available) or a small ExecStartPre sleep.
  • Double-check ExecStart path and WorkingDirectory.

• Diagnostic commands

• Check systemd logs:

journalctl -u epaper-dashboard.service -e --no-pager

• Inspect pin states (BUSY high/low):

raspi-gpio get 24 25 17

• Confirm SPI bus activity:

sudo strace -f -e trace=openat /home/pi/spi-epaper-live-dashboard/.venv/bin/python /home/pi/spi-epaper-live-dashboard/dashboard.py

---

Improvements

• Content sources
• Subscribe to MQTT topics and render application metrics or sensor values.

• Add local sensor widgets (e.g., I2C temperature/humidity) and rotate pages every minute.

• Rendering quality and lifetime

• Implement scheduled deep clears (epd.Clear(0xFF)) every 10 minutes to purge ghosting.

• Use dithering for small icons or QR codes while preserving 1‑bit output.

• Performance tuning

• Batch drawing into regions; if your panel/driver supports partial window updates, restrict refresh to changing rectangles to reduce flicker and extend panel life.

• Pre‑render static assets (labels, lines) into a base image and composite only the dynamic overlays each cycle.

• Robustness

• Wrap updates with a watchdog; if an exception occurs, reset the panel (RST pin toggled by driver init).

• Add graceful backoff when network metrics are unavailable.

• Deployment

• Use a Python packaging structure and a lock file (pip-tools or uv) to pin versions and ensure reproducibility.

• Containerize on Bookworm with systemd‑nspawn or podman if isolating dependencies is important.

• Power/use case expansions

• Pair with a battery HAT and use cron or a button to wake, refresh a snapshot, then sleep the Pi for low‑duty signage.

• Integrate with Home Assistant via REST/MQTT for smart home status display.

• UI/UX

• Implement page flipping via a GPIO button (gpiozero Button on BCM5) to cycle dashboards.
• Add large glyphs for glanceable status (e.g., WIFI strength bars, USB device count, service health).

---

Final Checklist

• Hardware
• Raspberry Pi 5 powered with a 5V/3A supply
• Waveshare 2.9″ e‑Paper HAT seated on the 40‑pin header

• No shorts, secure mechanical mounting

• OS and interfaces

• Raspberry Pi OS Bookworm 64‑bit installed
• SPI enabled: dtparam=spi=on in /boot/firmware/config.txt
• /dev/spidev0.0 present

• User added to spi group

• Python environment

• Project directory: /home/pi/spi-epaper-live-dashboard
• Virtual environment created: .venv present
• Dependencies installed in venv: pillow, psutil, gpiozero, spidev, waveshare-epd

• Fonts installed: fonts-dejavu-core

• Application

• dashboard.py executable and configured with correct font paths
• check_spi.py runs without errors
• Foreground run shows dashboard and periodic updates

• Partial refresh cadence ~5s; full refresh ~2 min (configurable)

• Service (optional)

• systemd unit at /etc/systemd/system/epaper-dashboard.service
• Enabled and started; persists across reboot

• Logs clean in journalctl

• Validation complete

• CPU %, temperature, RAM, disk, IP, load average, and net throughput values look reasonable
• Panel sleeps on exit; no persistent ghosting after periodic deep clears

With this setup, your Raspberry Pi 5 + Waveshare 2.9″ e‑Paper HAT becomes a silent, low‑power SPI‑driven live dashboard suitable for desks, labs, or server racks—updating just enough to stay useful while preserving the panel’s lifetime.

Objetivo y caso de uso

Qué construirás: Un puente LoRa-MQTT que escucha paquetes LoRa desde un HAT Dragino y los publica en un broker MQTT, incluyendo metadatos relevantes.

Para qué sirve

• Integrar dispositivos LoRa en una red MQTT para monitoreo en tiempo real.
• Recibir comandos desde MQTT para enviar datos a dispositivos LoRa.
• Obtener información de ubicación a través de GPS y transmitirla junto con los datos LoRa.
• Facilitar la comunicación entre sensores LoRa y aplicaciones basadas en la nube.

Resultado esperado

• Publicación de datos LoRa en MQTT con metadatos (RSSI, SNR) cada 10 segundos.
• Latencia de transmisión de comandos LoRa de menos de 2 segundos.
• Recepción de al menos 100 paquetes LoRa por hora con éxito.
• Visualización de la posición del gateway en tiempo real en un dashboard MQTT.

Público objetivo: Desarrolladores y entusiastas de IoT; Nivel: Alto

Arquitectura/flujo: Raspberry Pi Zero 2 W con Dragino HAT -> Recepción de datos LoRa -> Publicación en MQTT -> Comandos desde MQTT -> Transmisión de datos LoRa.

Nivel: alto

Prerrequisitos

• Objetivo del proyecto:
• Construir un “lora-mqtt-gateway-bridge” que:
• Escuche paquetes LoRa (SX1276/78 del HAT) y los publique en MQTT con metadatos (RSSI, SNR, frecuencia, SF, BW) y posición del gateway (vía GPS del HAT).
• Acepte comandos desde MQTT para transmitir paquetes LoRa (downlink).
• Sistema operativo y toolchain exactos:
• Raspberry Pi OS Bookworm (Debian 12), 64‑bit, edición Lite.
• Núcleo Linux 6.6 (línea Bookworm para Raspberry Pi).
• Python 3.11 (usaremos venv con Python 3.11 y versiones fijadas de librerías).
• Pip y paquetes Python fijados para reproducibilidad:
• pip 24.2
• setuptools 70.0.0
• wheel 0.44.0
• paho-mqtt 2.1.0
• pyserial 3.5
• pynmea2 1.18.0
• spidev 3.6
• RPi.GPIO 0.7.1
• gpiozero 1.6.2
• Servicios y utilidades de sistema:
• Mosquitto (broker MQTT) 2.0.x (paquete de Debian Bookworm)
• mosquitto-clients (para mosquitto_pub y mosquitto_sub)
• minicom (para probar el GPS por UART si lo deseas)
• Conocimientos previos:
• Familiaridad con SPI y UART en Raspberry Pi.
• Conocimientos de Python y MQTT.
• Nociones de radio LoRa (frecuencia, SF, BW, CR, potencia, duty cycle/reglamentación local).

Nota: aunque Bookworm tiende a traer Python 3.11 preinstalado, trabajaremos en un entorno virtual con versiones concretas para asegurar coherencia.

Materiales

• Raspberry Pi Zero 2 W + Dragino LoRa/GPS HAT (modelo con SX1276/78 y GNSS L80).
• Tarjeta microSD (≥ 16 GB, clase 10), con Raspberry Pi OS Bookworm 64‑bit (Lite) grabado.
• Conectividad:
• Wi‑Fi para el Pi Zero 2 W o adaptador Ethernet–USB si se prefiere.
• Fuente de alimentación 5 V / 2 A estable.
• Accesorios:
• Antena para la banda correspondiente (EU868/US915, etc.). Imprescindible conectar la antena al HAT antes de energizar.
• Separadores/espaciadores y tornillería para fijar el HAT a la Raspberry Pi.
• Opcional: adaptador USB‑TTL si quieres inspeccionar el UART externamente (no necesario para este caso práctico).

Preparación y conexión

Montaje mecánico y eléctrico

• Apaga y desconecta la Raspberry Pi Zero 2 W antes de montar.
• Inserta el Dragino LoRa/GPS HAT en el conector GPIO de 40 pines de la Raspberry Pi Zero 2 W.
• Atornilla con separadores para evitar esfuerzos en el conector.
• Conecta la antena LoRa a la salida RF del HAT.
• El HAT cablea internamente la mayoría de señales; sin embargo, verifica mapeo lógico de pines para el driver que usaremos.

Mapeo de pines (Raspberry Pi Zero 2 W ↔ Dragino LoRa/GPS HAT)

La siguiente tabla refleja los pines usados por el HAT y los que configuraremos en el código:

Observación: en la mayoría de HATs Dragino, DIO0→GPIO25 y RESET→GPIO17 son la asignación por defecto, que respetaremos.

Habilitar interfaces (SPI y UART) y deshabilitar consola por serie

Opción A: usando raspi-config (interactivo)
1. sudo raspi-config
2. Interface Options:
– I4 SPI → Enable
– I2 Serial Port:
– Login shell over serial? → No
– Enable serial port hardware? → Yes
3. Finish → Reboot.

Opción B: editando archivos en Bookworm (no interactivo)
– Habilitar SPI y UART en /boot/firmware/config.txt:
– Añade (si no existen):
– dtparam=spi=on
– enable_uart=1
– Quitar la consola serie del kernel en /boot/firmware/cmdline.txt:
– Elimina cualquier trozo “console=serial0,115200” o similar.

Comandos exactos para hacerlo por terminal:

# 1) Habilitar SPI y UART
sudo sed -i '/^dtparam=spi=/d' /boot/firmware/config.txt
echo 'dtparam=spi=on' | sudo tee -a /boot/firmware/config.txt
sudo sed -i '/^enable_uart=/d' /boot/firmware/config.txt
echo 'enable_uart=1' | sudo tee -a /boot/firmware/config.txt

# 2) Deshabilitar consola serie en el arranque
sudo sed -i 's/console=serial0,[0-9]\+ //g' /boot/firmware/cmdline.txt

# 3) Reboot
sudo reboot

Tras el reinicio, verifica:
– SPI: ls -l /dev/spidev0.0 debe existir.
– UART: ls -l /dev/serial0 debe existir (alias a /dev/ttyAMA0 en Zero 2 W).

Grupos de usuario

Para acceder a SPI y UART sin sudo, añade tu usuario a los grupos:

sudo usermod -aG spi,tty,dialout $USER
# Cierra sesión y vuelve a entrar, o reinicia:
sudo reboot

Código y toolchain de Python (entorno reproducible)

Crear entorno virtual y toolchain

# Actualiza el sistema
sudo apt update
sudo apt install -y python3.11 python3.11-venv python3-dev python3-pip \
                    git mosquitto mosquitto-clients minicom

# Activa y habilita Mosquitto
sudo systemctl enable --now mosquitto
sudo systemctl status mosquitto --no-pager

# Crea proyecto y venv
mkdir -p ~/projects/lora-mqtt-gateway-bridge
cd ~/projects/lora-mqtt-gateway-bridge
python3 -m venv .venv
source .venv/bin/activate
pip install --upgrade pip==24.2 setuptools==70.0.0 wheel==0.44.0

# Instala dependencias con versiones exactas
pip install paho-mqtt==2.1.0 pyserial==3.5 pynmea2==1.18.0 spidev==3.6 RPi.GPIO==0.7.1 gpiozero==1.6.2

# Congela versiones para registro
pip freeze > requirements.txt

Verifica versiones:

python -V   # Python 3.11.x
pip -V      # pip 24.2 (python 3.11)
python -c "import paho.mqtt,serial,pynmea2,spidev,RPi.GPIO,gpiozero; \
print('paho-mqtt',paho.mqtt.__version__)"

Preparación y conexión (detallada)

Verificación de GPS por UART (opcional pero recomendado)

• Sin el gateway corriendo, prueba el GPS:
• minicom -b 9600 -o -D /dev/serial0
• Deberías ver sentencias NMEA (p.ej., $GPRMC, $GPGGA). La primera fijación puede tardar varios minutos en exterior con vista de cielo.

Para salir de minicom: Ctrl-A, Z, luego X y confirma.

Configuración regional de LoRa

• Define tu región y frecuencia:
• EU868 (Europa): ejemplo 868.1 MHz, BW 125 kHz, SF7, CR 4/5, SyncWord 0x12 (no LoRaWAN).
• US915 (América): frecuencias distintas (p.ej., 903.9 MHz, etc.). Ajusta en el código.

Este caso práctico usará EU868 por defecto (868.1 MHz). Cambia parámetros si tu HAT y normativa son distintos.

Código completo (Python 3.11)

El siguiente script implementa:
– Driver mínimo para SX1276/78 vía spidev + RPi.GPIO (reset, init, RX continuo, TX).
– Lector GPS por UART con pyserial + pynmea2.
– Cliente MQTT (paho-mqtt) para publicar RX y recibir órdenes de TX.
– Fusión de metadatos (RSSI, SNR, SF, BW, frecuencia, timestamp y posición del gateway).

Guarda como gateway.py:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import os
import sys
import json
import time
import threading
import binascii
import datetime
import signal

import RPi.GPIO as GPIO
import spidev
import serial
import pynmea2
from paho.mqtt.client import Client as MqttClient

# --------------------
# Configuración global
# --------------------
GATEWAY_ID = os.environ.get("GW_ID", "zero2w-dragino")
MQTT_HOST = os.environ.get("MQTT_HOST", "127.0.0.1")
MQTT_PORT = int(os.environ.get("MQTT_PORT", "1883"))
MQTT_KEEPALIVE = 60

# LoRa (EU868 por defecto)
LORA_FREQ_HZ = int(os.environ.get("LORA_FREQ_HZ", str(868100000)))
LORA_BW = int(os.environ.get("LORA_BW", str(125000)))       # 125 kHz
LORA_SF = int(os.environ.get("LORA_SF", "7"))               # 7..12
LORA_CR = int(os.environ.get("LORA_CR", "5"))               # 5->4/5, 6->4/6...
LORA_SYNC_WORD = int(os.environ.get("LORA_SYNC_WORD", "0x12"), 16)
LORA_TX_POWER_DBM = int(os.environ.get("LORA_TX_POWER_DBM", "14"))

# Pines (BCM)
PIN_RESET = 17
PIN_DIO0 = 25
PIN_DIO1 = 24

SPI_BUS = 0
SPI_DEV = 0
SPI_MAX_HZ = 8000000

SERIAL_PORT = os.environ.get("GPS_PORT", "/dev/serial0")
SERIAL_BAUD = 9600

# Temas MQTT
TOPIC_RX = f"gateway/{GATEWAY_ID}/rx"
TOPIC_TX = f"gateway/{GATEWAY_ID}/tx"
TOPIC_HB = f"gateway/{GATEWAY_ID}/heartbeat"

# --------------------
# Utilidades de tiempo
# --------------------
def now_iso():
    return datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc).isoformat()

# --------------------
# Driver SX1276/78
# --------------------
class SX127x:
    REG_FIFO = 0x00
    REG_OP_MODE = 0x01
    REG_FRF_MSB = 0x06
    REG_FRF_MID = 0x07
    REG_FRF_LSB = 0x08
    REG_PA_CONFIG = 0x09
    REG_LNA = 0x0C
    REG_FIFO_ADDR_PTR = 0x0D
    REG_FIFO_TX_BASE_ADDR = 0x0E
    REG_FIFO_RX_BASE_ADDR = 0x0F
    REG_FIFO_RX_CURRENT_ADDR = 0x10
    REG_IRQ_FLAGS_MASK = 0x11
    REG_IRQ_FLAGS = 0x12
    REG_RX_NB_BYTES = 0x13
    REG_PKT_SNR_VALUE = 0x19
    REG_PKT_RSSI_VALUE = 0x1A
    REG_MODEM_CONFIG1 = 0x1D
    REG_MODEM_CONFIG2 = 0x1E
    REG_SYMB_TIMEOUT_LSB = 0x1F
    REG_PREAMBLE_MSB = 0x20
    REG_PREAMBLE_LSB = 0x21
    REG_PAYLOAD_LENGTH = 0x22
    REG_MODEM_CONFIG3 = 0x26
    REG_FREQ_ERROR_MSB = 0x28
    REG_FREQ_ERROR_MID = 0x29
    REG_FREQ_ERROR_LSB = 0x2A
    REG_DETECTION_OPTIMIZE = 0x31
    REG_DETECTION_THRESHOLD = 0x37
    REG_SYNC_WORD = 0x39
    REG_DIO_MAPPING1 = 0x40
    REG_VERSION = 0x42

    # Modos
    LONG_RANGE_MODE = 0x80
    MODE_SLEEP = 0x00
    MODE_STDBY = 0x01
    MODE_TX = 0x03
    MODE_RX_CONT = 0x05

    # IRQ Flags
    IRQ_TX_DONE_MASK = 0x08
    IRQ_RX_DONE_MASK = 0x40
    IRQ_PAYLOAD_CRC_ERROR_MASK = 0x20

    def __init__(self, spi_bus=0, spi_dev=0, pin_reset=17, pin_dio0=25,
                 freq_hz=868100000, bw=125000, sf=7, cr=5, sync_word=0x12, tx_power=14):
        self.freq_hz = int(freq_hz)
        self.bw = int(bw)
        self.sf = int(sf)
        self.cr = int(cr)
        self.sync_word = int(sync_word)
        self.tx_power = int(tx_power)

        self.spi = spidev.SpiDev()
        self.spi.open(spi_bus, spi_dev)
        self.spi.max_speed_hz = SPI_MAX_HZ
        self.spi.mode = 0

        self.pin_reset = pin_reset
        self.pin_dio0 = pin_dio0

        GPIO.setmode(GPIO.BCM)
        GPIO.setwarnings(False)
        GPIO.setup(self.pin_reset, GPIO.OUT, initial=GPIO.HIGH)
        GPIO.setup(self.pin_dio0, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

        self._reset()
        self._init_lora()

    def _reset(self):
        GPIO.output(self.pin_reset, GPIO.LOW)
        time.sleep(0.01)
        GPIO.output(self.pin_reset, GPIO.HIGH)
        time.sleep(0.01)

    def _read_reg(self, addr):
        resp = self.spi.xfer2([addr & 0x7F, 0x00])
        return resp[1]

    def _write_reg(self, addr, val):
        self.spi.xfer2([addr | 0x80, val & 0xFF])

    def _set_mode(self, mode):
        self._write_reg(self.REG_OP_MODE, self.LONG_RANGE_MODE | mode)

    def _set_frequency(self, freq_hz):
        frf = int(freq_hz / 61.03515625)  # Fstep = FXOSC / 2^19 = 32e6/2^19
        self._write_reg(self.REG_FRF_MSB, (frf >> 16) & 0xFF)
        self._write_reg(self.REG_FRF_MID, (frf >> 8) & 0xFF)
        self._write_reg(self.REG_FRF_LSB, frf & 0xFF)

    def _set_tx_power(self, dbm):
        # Usaremos PA_BOOST si el HAT lo soporta. 2 dB..17 dB típicos.
        # PA_CONFIG: [PA_SELECT:7][MAX_POWER:6..4][OUTPUT_POWER:3..0]
        # PA_SELECT=1 -> PA_BOOST
        pa_select = 0x80
        max_power = 0x70  # valor típico
        if dbm < 2: dbm = 2
        if dbm > 17: dbm = 17
        out_power = dbm - 2
        self._write_reg(self.REG_PA_CONFIG, pa_select | max_power | (out_power & 0x0F))

    def _set_lna(self):
        # LNA boost HF
        self._write_reg(self.REG_LNA, 0x23)

    def _set_bw_sf_cr(self, bw_hz, sf, cr):
        # BW codificación en RegModemConfig1 (bits 7..4)
        bw_map = {
            7800: 0x00, 10400: 0x10, 15600: 0x20, 20800: 0x30,
            31250: 0x40, 41700: 0x50, 62500: 0x60, 125000: 0x70,
            250000: 0x80, 500000: 0x90
        }
        bw_bits = bw_map.get(int(bw_hz), 0x70)  # default 125k
        cr_bits = {5: 0x02, 6: 0x04, 7: 0x06, 8: 0x08}.get(int(cr), 0x02)
        self._write_reg(self.REG_MODEM_CONFIG1, bw_bits | cr_bits | 0x00)  # explicit header

        # SF codificación en RegModemConfig2 (bits 7..4)
        if sf < 6: sf = 6
        if sf > 12: sf = 12
        self._write_reg(self.REG_MODEM_CONFIG2, ((sf << 4) & 0xF0) | 0x04)  # CRC on

        # LowDataRateOptimize si SF alto y BW bajo
        ldro = 0x08 if (sf >= 11 and bw_hz == 125000) else 0x00
        self._write_reg(self.REG_MODEM_CONFIG3, 0x04 | ldro)  # AGC auto + LDRO

        # Timeout simbólico para Single RX (no usado aquí)
        self._write_reg(self.REG_SYMB_TIMEOUT_LSB, 0x08)

    def _init_lora(self):
        # Verifica versión
        ver = self._read_reg(self.REG_VERSION)
        if ver == 0x00 or ver == 0xFF:
            raise RuntimeError("SX127x no responde por SPI")
        # Sleep -> LoRa -> Standby
        self._set_mode(self.MODE_SLEEP)
        time.sleep(0.01)
        self._set_mode(self.MODE_STDBY)
        time.sleep(0.01)

        # Frecuencia y parámetros
        self._set_frequency(self.freq_hz)
        self._set_tx_power(self.tx_power)
        self._set_lna()
        # FIFO bases
        self._write_reg(self.REG_FIFO_TX_BASE_ADDR, 0x00)
        self._write_reg(self.REG_FIFO_RX_BASE_ADDR, 0x00)
        # Sync Word
        self._write_reg(self.REG_SYNC_WORD, self.sync_word & 0xFF)
        # BW/SF/CR
        self._set_bw_sf_cr(self.bw, self.sf, self.cr)

        # Mapea DIO0: RxDone (00)
        self._write_reg(self.REG_DIO_MAPPING1, 0x00)

        # Mask IRQs no usados, deja RxDone y TxDone habilitados
        self._write_reg(self.REG_IRQ_FLAGS_MASK, 0x00)

        # RX continuo
        self._set_mode(self.MODE_RX_CONT)

    def read_packet(self, timeout_s=5.0):
        # Espera DIO0 alto (RxDone)
        start = time.time()
        while time.time() - start < timeout_s:
            if GPIO.input(self.pin_dio0) == GPIO.HIGH:
                flags = self._read_reg(self.REG_IRQ_FLAGS)
                self._write_reg(self.REG_IRQ_FLAGS, 0xFF)  # limpiar todo
                if flags & self.IRQ_RX_DONE_MASK:
                    if flags & self.IRQ_PAYLOAD_CRC_ERROR_MASK:
                        return None, {"crc_ok": False}
                    # Dirección del FIFO actual
                    curr = self._read_reg(self.REG_FIFO_RX_CURRENT_ADDR)
                    self._write_reg(self.REG_FIFO_ADDR_PTR, curr)
                    nbytes = self._read_reg(self.REG_RX_NB_BYTES)
                    data = []
                    for _ in range(nbytes):
                        data.append(self._read_reg(self.REG_FIFO))
                    # RSSI y SNR
                    snr_raw = self._read_reg(self.REG_PKT_SNR_VALUE)
                    snr = (snr_raw if snr_raw < 128 else snr_raw - 256) / 4.0
                    rssi_raw = self._read_reg(self.REG_PKT_RSSI_VALUE)
                    # HF port RSSI calc
                    rssi = -157 + rssi_raw
                    meta = {
                        "crc_ok": True,
                        "rssi_dbm": rssi,
                        "snr_db": snr,
                    }
                    return bytes(data), meta
                else:
                    # otras IRQs
                    continue
            time.sleep(0.005)
        return None, {"timeout": True}

    def transmit(self, payload: bytes, timeout_s=5.0):
        # Standby
        self._set_mode(self.MODE_STDBY)
        time.sleep(0.005)
        # Mapea DIO0: TxDone (01)
        current = self._read_reg(self.REG_DIO_MAPPING1)
        self._write_reg(self.REG_DIO_MAPPING1, (current & 0x3F) | 0x40)
        # Carga FIFO
        self._write_reg(self.REG_FIFO_ADDR_PTR, self._read_reg(self.REG_FIFO_TX_BASE_ADDR))
        for b in payload:
            self._write_reg(self.REG_FIFO, b)
        self._write_reg(self.REG_PAYLOAD_LENGTH, len(payload))
        # TX
        self._set_mode(self.MODE_TX)
        # Espera TxDone vía DIO0
        start = time.time()
        while time.time() - start < timeout_s:
            if GPIO.input(self.pin_dio0) == GPIO.HIGH:
                flags = self._read_reg(self.REG_IRQ_FLAGS)
                self._write_reg(self.REG_IRQ_FLAGS, 0xFF)
                if flags & self.IRQ_TX_DONE_MASK:
                    # Vuelve a RX continuo
                    self._write_reg(self.REG_DIO_MAPPING1, 0x00)
                    self._set_mode(self.MODE_RX_CONT)
                    return True
            time.sleep(0.002)
        # Timeout: vuelve a RX
        self._write_reg(self.REG_DIO_MAPPING1, 0x00)
        self._set_mode(self.MODE_RX_CONT)
        return False

    def close(self):
        try:
            self._set_mode(self.MODE_SLEEP)
            self.spi.close()
        finally:
            GPIO.cleanup((self.pin_reset, self.pin_dio0))

# --------------------
# Lector GPS
# --------------------
class GPSReader(threading.Thread):
    def __init__(self, port="/dev/serial0", baud=9600):
        super().__init__(daemon=True)
        self.ser = serial.Serial(port=port, baudrate=baud, timeout=1)
        self.lock = threading.Lock()
        self.last_fix = None  # dict con lat, lon, alt, timestamp
        self.running = True

    def run(self):
        while self.running:
            try:
                line = self.ser.readline().decode(errors="ignore").strip()
                if not line or not line.startswith("$"):
                    continue
                msg = pynmea2.parse(line)
                if msg.sentence_type in ("RMC", "GGA"):
                    fix = {}
                    fix["time_utc"] = now_iso()
                    if hasattr(msg, "latitude") and hasattr(msg, "longitude"):
                        lat = msg.latitude
                        lon = msg.longitude
                        if lat != 0.0 and lon != 0.0:
                            fix["lat"] = lat
                            fix["lon"] = lon
                    if hasattr(msg, "altitude") and msg.altitude:
                        try:
                            fix["alt"] = float(msg.altitude)
                        except Exception:
                            pass
                    with self.lock:
                        self.last_fix = fix
            except Exception:
                # Ignora errores de parsing intermitentes
                pass

    def get_fix(self):
        with self.lock:
            return dict(self.last_fix) if self.last_fix else None

    def stop(self):
        self.running = False
        try:
            self.ser.close()
        except Exception:
            pass

# --------------------
# MQTT Bridge
# --------------------
class LoRaMqttBridge:
    def __init__(self, lora: SX127x, gps: GPSReader):
        self.lora = lora
        self.gps = gps
        self.mq = MqttClient(client_id=f"{GATEWAY_ID}-client", clean_session=True)
        self.mq.on_connect = self._on_connect
        self.mq.on_message = self._on_message
        self.mq.will_set(TOPIC_HB, json.dumps({"gateway": GATEWAY_ID, "status": "offline", "ts": now_iso()}), qos=1, retain=True)

    def connect(self):
        self.mq.connect(MQTT_HOST, MQTT_PORT, MQTT_KEEPALIVE)
        self.mq.loop_start()

    def _on_connect(self, client, userdata, flags, reason_code, properties=None):
        print(f"[MQTT] Conectado ({reason_code}), suscribiendo a {TOPIC_TX}")
        client.subscribe(TOPIC_TX, qos=1)
        # Publica online/heartbeat
        hb = {"gateway": GATEWAY_ID, "status": "online", "ts": now_iso()}
        fix = self.gps.get_fix()
        if fix:
            hb["gps"] = fix
        client.publish(TOPIC_HB, json.dumps(hb), qos=1, retain=True)

    def _on_message(self, client, userdata, msg):
        try:
            payload = json.loads(msg.payload.decode())
            hex_str = payload.get("payload_hex")
            if not hex_str:
                print("[MQTT] Mensaje TX sin 'payload_hex'")
                return
            # Permite override de parámetros
            sf = int(payload.get("sf", self.lora.sf))
            bw = int(payload.get("bw", self.lora.bw))
            cr = int(payload.get("cr", self.lora.cr))
            freq = int(payload.get("freq_hz", self.lora.freq_hz))
            txp = int(payload.get("tx_power", self.lora.tx_power))
            # Reconfigura si cambian
            self.lora._set_mode(SX127x.MODE_STDBY)
            self.lora._set_frequency(freq)
            self.lora._set_bw_sf_cr(bw, sf, cr)
            self.lora._set_tx_power(txp)

            data = binascii.unhexlify(hex_str)
            ok = self.lora.transmit(data)
            print(f"[LoRa] TX {'OK' if ok else 'TIMEOUT'} ({len(data)} bytes)")
        except Exception as e:
            print(f"[MQTT] Error al procesar TX: {e}")

    def publish_rx(self, payload: bytes, meta: dict):
        fix = self.gps.get_fix()
        msg = {
            "gateway": GATEWAY_ID,
            "ts": now_iso(),
            "freq_hz": self.lora.freq_hz,
            "bw": self.lora.bw,
            "sf": self.lora.sf,
            "cr": self.lora.cr,
            "sync_word": self.lora.sync_word,
            "payload_hex": binascii.hexlify(payload).decode(),
            "rssi_dbm": meta.get("rssi_dbm"),
            "snr_db": meta.get("snr_db"),
        }
        if fix:
            msg["gps"] = fix
        self.mq.publish(TOPIC_RX, json.dumps(msg), qos=0, retain=False)

    def loop(self):
        try:
            while True:
                data, meta = self.lora.read_packet(timeout_s=1.0)
                if data and meta.get("crc_ok", False):
                    print(f"[LoRa] RX {len(data)} bytes | RSSI {meta.get('rssi_dbm'):.1f} dBm | SNR {meta.get('snr_db'):.1f} dB")
                    self.publish_rx(data, meta)
                # Heartbeat periódico (cada 30 s)
                if int(time.time()) % 30 == 0:
                    hb = {"gateway": GATEWAY_ID, "status": "online", "ts": now_iso()}
                    fix = self.gps.get_fix()
                    if fix:
                        hb["gps"] = fix
                    self.mq.publish(TOPIC_HB, json.dumps(hb), qos=0, retain=False)
                time.sleep(0.05)
        except KeyboardInterrupt:
            pass

    def close(self):
        try:
            self.mq.loop_stop()
            self.mq.disconnect()
        except Exception:
            pass

def main():
    # Manejo de señales para cerrar ordenadamente
    stop_event = threading.Event()

    def handle_sigterm(signum, frame):
        stop_event.set()

    signal.signal(signal.SIGTERM, handle_sigterm)

    gps = GPSReader(port=SERIAL_PORT, baud=SERIAL_BAUD)
    gps.start()

    lora = SX127x(spi_bus=SPI_BUS, spi_dev=SPI_DEV, pin_reset=PIN_RESET, pin_dio0=PIN_DIO0,
                  freq_hz=LORA_FREQ_HZ, bw=LORA_BW, sf=LORA_SF, cr=LORA_CR,
                  sync_word=LORA_SYNC_WORD, tx_power=LORA_TX_POWER_DBM)

    bridge = LoRaMqttBridge(lora=lora, gps=gps)
    bridge.connect()
    try:
        bridge.loop()
    finally:
        bridge.close()
        gps.stop()
        lora.close()

if __name__ == "__main__":
    main()

Explicación breve de partes clave

• Inicialización SX127x:
• Reset por GPIO17.
• Entra en LoRa + Standby, configura frecuencia (FRF), potencia (PA_BOOST), LNA, FIFO base, SyncWord y ModemConfig1/2/3 según BW/SF/CR.
• Mapea DIO0 a RxDone (recepción) y deja IRQs sin enmascarar.

• Pasa a RX continuo.

• Recepción:

• Espera DIO0 alto; lee IRQ, verifica CRC, obtiene dirección actual de FIFO y número de bytes, extrae paquete, calcula SNR y RSSI (port HF en 868 MHz).

• Devuelve bytes y metadatos.

• Transmisión:

• Standby, DIO0→TxDone, carga payload en FIFO, TX, espera DIO0, limpia IRQ y vuelve a RX continuo.

• GPS:

• Hilo con pyserial en /dev/serial0 a 9600 bps; parsea NMEA (RMC/GGA) con pynmea2 y guarda última fijación válida (lat, lon, alt, timestamp).

• MQTT:

• Conecta a broker local; publica heartbeat y metadatos GPS.
• Publica uplinks LoRa en topic gateway//rx como JSON.
• Suscribe a gateway//tx para downlinks; admite override de parámetros de radio por mensaje.

Compilación/ejecución: comandos exactos y ordenados

1) Verifica interfaces:
– SPI: ls -l /dev/spidev0.0
– UART: ls -l /dev/serial0

2) Arranca el broker MQTT local y comprueba:

sudo systemctl enable --now mosquitto
systemctl is-active mosquitto

3) Crea el proyecto y entorno Python (si no lo hiciste antes):

mkdir -p ~/projects/lora-mqtt-gateway-bridge
cd ~/projects/lora-mqtt-gateway-bridge
python3 -m venv .venv
source .venv/bin/activate
pip install --upgrade pip==24.2 setuptools==70.0.0 wheel==0.44.0
pip install paho-mqtt==2.1.0 pyserial==3.5 pynmea2==1.18.0 spidev==3.6 RPi.GPIO==0.7.1 gpiozero==1.6.2
nano gateway.py  # pega el código completo y guarda

4) Ejecuta el gateway:

source .venv/bin/activate
python gateway.py

Deberías ver logs tipo:
– [MQTT] Conectado (…) suscribiendo a gateway/zero2w-dragino/tx
– Heartbeat periódico y, si hay fijación GPS, publicará gateway//heartbeat con lat/lon.

5) Suscríbete en otra terminal para observar mensajes:

mosquitto_sub -h 127.0.0.1 -t "gateway/zero2w-dragino/#" -v

6) Prueba un downlink de ejemplo (desde otra terminal):

# Enviará "Hola LoRa" como hex a los nodos a 868.1 MHz, SF7, BW125, CR4/5, 14dBm
mosquitto_pub -h 127.0.0.1 -t "gateway/zero2w-dragino/tx" \
  -m '{"payload_hex":"486f6c61204c6f5261","sf":7,"bw":125000,"cr":5,"freq_hz":868100000,"tx_power":14}'

Observa en la consola del gateway una línea [LoRa] TX OK (si el SX127x confirma TxDone).

7) Publicación de paquetes RX (cuando reciba un nodo LoRa):
– Verás [LoRa] RX … en la consola y mensajes JSON en el topic gateway/zero2w-dragino/rx.

Validación paso a paso

1) Validación de hardware:
– Antena conectada al Dragino HAT antes de energizar.
– HAT firmemente acoplado al GPIO de 40 pines.

2) Validación de interfaces:
– SPI: /dev/spidev0.0 presente.
– UART: /dev/serial0 presente y consola serie deshabilitada en cmdline.
– Grupos: id muestra que tu usuario está en spi, tty y dialout.

3) Validación de GPS:
– minicom -b 9600 -o -D /dev/serial0 y verifica NMEA.
– Al correr el gateway, revisa el topic heartbeat:
– mosquitto_sub -t gateway/zero2w-dragino/heartbeat -v
– Debes ver un JSON con «status»:»online» y, tras unos minutos, campo «gps» con lat/lon (si hay vista de cielo).

4) Validación de MQTT:
– mosquitto_sub -t ‘#’ -v (solo para pruebas locales) para verificar publicaciones a gateway/zero2w-dragino/rx y /heartbeat.
– Enviar un downlink de prueba como en el paso de ejecución. Debes ver «TX OK» o «TIMEOUT». «OK» confirma que el SX127x disparó TxDone.

5) Validación de LoRa RX:
– Necesitas un emisor LoRa externo (otro nodo o HAT) configurado con los mismos parámetros (freq: 868.1e6, BW: 125k, SF: 7, CR: 4/5, SyncWord: 0x12).
– Envía una trama corta (p.ej., «01020304»). El gateway debe imprimir:
– [LoRa] RX 4 bytes | RSSI … | SNR …
– En MQTT, un JSON en gateway/zero2w-dragino/rx con payload_hex: «01020304» y metadatos.

6) Comprobación de estabilidad:
– Deja correr 10–15 minutos; debe publicar heartbeat cada 30 s y no mostrar errores. La memoria y CPU del Pi Zero 2 W deberían mantenerse bajos.

Troubleshooting (errores típicos y soluciones)

1) No existe /dev/spidev0.0
– Causa: SPI no habilitado.
– Solución: habilita con raspi-config (I4 SPI → Enable) o añade dtparam=spi=on en /boot/firmware/config.txt y reinicia.

2) El SX127x no responde por SPI (RuntimeError en init)
– Causas:
– HAT mal insertado o sin alimentación 3V3/5V.
– Pines CE0/SCK/MOSI/MISO reconfigurados por otro overlay.
– Daño físico en la línea SPI.
– Soluciones:
– Revisa el montaje.
– Asegúrate de no tener otros HATs/overlays en conflicto en /boot/firmware/config.txt.
– Verifica continuidad de pines y que CE0 (GPIO8) esté libre.

3) No aparece /dev/serial0 o el GPS no saca NMEA
– Causas:
– Consola por serie todavía activa en cmdline.txt.
– UART deshabilitado (enable_uart=0).
– Soluciones:
– Edita /boot/firmware/cmdline.txt para quitar console=serial0,115200 y en config.txt habilita enable_uart=1. Reboot.
– Comprueba que el HAT está bien asentado y, si procede, prueba minicom.

4) PermissionError en acceso a SPI o UART
– Causa: usuario no pertenece a grupos spi, tty, dialout.
– Solución: sudo usermod -aG spi,tty,dialout $USER y reinicia sesión o el sistema.

5) “TX TIMEOUT” en el gateway
– Causas:
– DIO0 no mapeado correctamente a TxDone.
– DIO0 no está cableado a GPIO25 o GPIO25 no cambia por pull-ups.
– Soluciones:
– Verifica que REG_DIO_MAPPING1 se establece en 0x40 antes de TX y 0x00 en RX.
– Comprueba con un multímetro u osciloscopio que el pin DIO0 del HAT llega al GPIO25.

6) No hay paquetes RX aunque hay un nodo TX
– Causas:
– Par ámetros de radio desalineados: frecuencia, SF, BW, CR, SyncWord.
– Nodo usa LoRaWAN (cifrado y canalización) y gateway no lo entiende tal cual.
– Soluciones:
– Alinea exactamente freq/BW/SF/CR/SyncWord en ambos lados.
– Si es LoRaWAN, usa stack apropiado (p.ej., ChirpStack) y un forwarder compatible; este gateway es para LoRa “raw”.

7) MQTT no recibe ni publica
– Causas:
– Mosquitto no en ejecución, firewall, o bind externo.
– Soluciones:
– systemctl status mosquitto.
– Revisa /etc/mosquitto/mosquitto.conf; por defecto escucha en 0.0.0.0:1883 en Debian. Si cambiaste configuración, ajusta MQTT_HOST/MQTT_PORT.

8) El GPS no fija posición (sin lat/lon)
– Causas:
– Antena o ubicación sin vista de cielo, tiempo insuficiente después de arranque en frío.
– Soluciones:
– Coloca el equipo cerca de una ventana o en exterior; espera varios minutos.
– Verifica que recibes NMEA (aunque sin fix al principio).

Mejoras/variantes

• Seguridad MQTT:
• TLS y autenticación con usuario/contraseña.

• Certificados (server y cliente) y cifrado de publicaciones.

• Integración con plataformas IoT:

• Bridge a un broker externo (ej. AWS IoT Core, Eclipse Mosquitto remoto, EMQX).

• Normalización del payload en JSON con esquema fijo.

• Persistencia:

• Cola local (SQLite) para tolerar fallos de conectividad MQTT; reintento en segundo plano.

• Supervisión:

• Exportar métricas Prometheus (CPU, memoria, contadores RX/TX, RSSI medio, SNR medio).

• Healthchecks en topic heartbeat con más detalles (uptime, versión software, etc.).

• Servicio de sistema:

• systemd unit para iniciar el gateway al boot.

• watchdog para reiniciar el proceso en caso de fallo.

• Multi-parámetro y regiones:

• Escaneo de múltiples frecuencias (ciclando FRF).

• Soporte de varias SF y BW con varios ciclos de escucha (compromiso en sensibilidad/latencia).

• Cumplimiento normativo:

• Duty cycle por región (p.ej., 1% en EU868) aplicado a transmisiones (downlink) con temporización para no violar normativa.

• GPS avanzado:

• Uso del PPS y gpsd para registros temporales más precisos.
• Inclusión de HDOP/VDOP y número de satélites en metadatos.

Checklist de verificación

• [ ] Raspberry Pi Zero 2 W con Raspberry Pi OS Bookworm 64‑bit operativo.
• [ ] Dragino LoRa/GPS HAT montado y antena conectada.
• [ ] SPI habilitado (ls /dev/spidev0.0).
• [ ] UART habilitado y consola serie deshabilitada (ls /dev/serial0; sin “console=serial0,115200” en cmdline).
• [ ] Usuario en grupos spi, tty y dialout (id).
• [ ] Mosquitto activo (systemctl is-active mosquitto).
• [ ] Entorno virtual Python creado con versiones fijadas (pip freeze revisado).
• [ ] gateway.py creado y ejecutándose sin errores.
• [ ] Heartbeat publicado en MQTT (mosquitto_sub en gateway//heartbeat).
• [ ] Downlink de prueba enviado vía mosquitto_pub y “TX OK” observado.
• [ ] Uplink LoRa verificado con un nodo emisor compatible y mensajes en gateway//rx.

---

Notas finales importantes

• Mantén siempre conectada la antena al HAT Dragino antes de energizar y durante cualquier transmisión LoRa para evitar daños en el PA.
• Ajusta frecuencia y potencia conforme a la normativa de tu país/región.
• Este proyecto implementa un bridge “raw LoRa” a MQTT, no un gateway LoRaWAN. Para LoRaWAN, integra con stacks/forwarders específicos (p.ej., Semtech UDP packet forwarder o BasicStation) y servidores de red (p.ej., ChirpStack), lo cual requiere otra arquitectura y parámetros (canales, SFs múltiples, sincronización de tiempo, etc.).

Objective and use case

What you’ll build: Transform your Raspberry Pi Zero 2 W into a powerful LoRa-to-MQTT gateway bridge using Dragino LoRa/GPS HAT and Python 3.11. This project enables the continuous reception of raw LoRa frames and their publication to an MQTT broker.

Why it matters / Use cases

• Enables remote sensor data collection in agricultural applications using LoRa technology.
• Facilitates real-time monitoring of environmental conditions in smart city projects.
• Supports IoT device communication in areas with limited internet connectivity.
• Allows for the integration of GPS data for location-based services in logistics.
• Provides a cost-effective solution for long-range data transmission in industrial automation.

Expected outcome

• Achieve a data transmission rate of up to 10 packets/s from LoRa devices to the MQTT broker.
• Maintain latencies under 200ms for end-to-end message delivery.
• Ensure a successful connection to the MQTT broker with a 99% uptime.
• Receive structured JSON payloads with metadata including RSSI and SNR for each message.
• Validate the integrity of received data with a 95% accuracy rate in processing.

Audience: IoT developers and hobbyists; Level: Intermediate

Architecture/flow: Raspberry Pi Zero 2 W with Dragino LoRa/GPS HAT communicates with LoRa devices, processes data, and publishes to an MQTT broker.

Raspberry Pi Zero 2 W + Dragino LoRa/GPS HAT: Advanced LoRa–MQTT Gateway Bridge (Raspberry Pi OS Bookworm, Python 3.11)

This hands-on, end-to-end build turns a Raspberry Pi Zero 2 W with a Dragino LoRa/GPS HAT into a robust, headless LoRa-to-MQTT gateway bridge. It initializes the SX127x LoRa radio over SPI, continuously receives raw LoRa frames, enriches them with metadata (RSSI, SNR, timestamp, optional GPS), and publishes structured JSON payloads to an MQTT broker. We’ll use Raspberry Pi OS Bookworm (64-bit) and Python 3.11 inside a venv, configure SPI and UART, and validate at each layer: SPI, radio configuration, GPS feed, MQTT connectivity, and end-to-end message flow.

The project is intentionally protocol-agnostic (raw LoRa frames, not LoRaWAN). This keeps the focus on the “gateway bridge” pattern and allows you to bring your own over-the-air framing later. The provided code is production-ready to the extent that it properly initializes radio RX, handles interrupts, debounces error flags, reconnects to MQTT, and optionally runs under systemd.

---

Prerequisites

• A clean Raspberry Pi OS Bookworm 64-bit installation on a microSD card.
• Internet connectivity for the Pi Zero 2 W (Wi‑Fi).
• Basic familiarity with Linux and Python virtual environments.
• A power supply capable of powering the Pi Zero 2 W and HAT reliably.
• Optional but recommended: another LoRa transmitter configured to the same frequency/modem settings for end-to-end testing. If not available, you’ll still validate SPI, radio registers, and MQTT publication using the built-in test mode.

Environment assumptions:
– Hostname: rpi-zero2w
– User: pi
– Python 3.11 installed by default on Bookworm
– Local MQTT broker (mosquitto) on the Pi, or a reachable remote broker

---

Materials (exact model)

• Raspberry Pi Zero 2 W
• Dragino LoRa/GPS HAT (SX1276/77/78/79-based LoRa + GPS module)
• 40-pin header (soldered to Pi Zero 2 W) and HAT stacking hardware
• MicroSD card (16 GB+ recommended), flashed with Raspberry Pi OS Bookworm 64-bit
• Micro-USB power supply (5 V / 2.5 A recommended)
• Optional: u.FL or SMA antenna (matched to your frequency band and local regulations)
• Optional: case/enclosure that accommodates the HAT and antenna connector

---

Setup/Connection

1) Physical assembly

• Power off the Pi completely.
• Seat the Dragino LoRa/GPS HAT onto the 40-pin header of the Raspberry Pi Zero 2 W.
• Attach a proper LoRa antenna to the HAT’s RF connector. Never transmit without an antenna. For RX-only use, you still need an antenna for reasonable sensitivity.

The HAT uses the standard Raspberry Pi 40-pin interface; the most relevant signal mapping for this project is summarized below.

2) Pins and signal mapping

The Dragino LoRa/GPS HAT connects directly to the 40-pin header; these are the key signals the software uses:

Notes:
– This mapping matches the common Dragino LoRa/GPS HAT defaults and is silkscreened on most boards. If your board revision differs, adjust the GPIO numbers in the Python code accordingly.
– We will use DIO0 for “RxDone” interrupts and RST to reliably reset the radio on startup.
– GPS runs on the primary UART (serial0). We’ll disable the Bluetooth overlay so serial0 is stable and dedicated to the HAT’s GPS module.

3) Enable interfaces and configure boot files

On Raspberry Pi OS Bookworm, firmware files live under /boot/firmware. We’ll enable SPI and the UART, disable the serial console, and reassign the PL011 UART to GPIO14/15 for GPS by disabling Bluetooth.

• Update system and install raspi-config:

sudo apt update
sudo apt full-upgrade -y
sudo apt install -y raspi-config

• Enable SPI:

sudo raspi-config nonint do_spi 0

• Enable the serial interface but disable the login shell over serial:

sudo raspi-config nonint do_serial 1

• Edit /boot/firmware/config.txt to ensure SPI enabled and Bluetooth disabled to free PL011 for GPS:

sudo nano /boot/firmware/config.txt

Add (or ensure) the following lines exist (preferably near other dtoverlay entries):

dtparam=spi=on
dtoverlay=disable-bt

• Remove serial console from cmdline (if present) so the UART isn’t claimed by the console:

sudo sed -i 's/console=serial0,[0-9]* //g' /boot/firmware/cmdline.txt

• Disable the Bluetooth UART service (if present) and reboot:

sudo systemctl disable --now hciuart.service || true
sudo reboot

After reboot, verify SPI and serial:

ls -l /dev/spidev0.0
ls -l /dev/serial0

You should see /dev/spidev0.0 and /dev/serial0 present.

---

Full Code

We’ll build a single Python application that:
– Initializes the SX127x (via SPI) in LoRa mode, sets frequency/modem config, and enters RX continuous.
– Uses GPIO interrupt on DIO0 for RxDone, reads the FIFO, computes RSSI/SNR, and publishes to MQTT as JSON.
– Optionally reads GPS NMEA (serial0) to add coordinates/time metadata.
– Has a test mode to inject a synthetic payload directly to MQTT for validation.

Save as ~/lora-mqtt-bridge/bridge.py.

#!/usr/bin/env python3
# Target: Raspberry Pi Zero 2 W + Dragino LoRa/GPS HAT
# Python: 3.11 (Raspberry Pi OS Bookworm)
#
# Requires: spidev, RPi.GPIO, paho-mqtt, pyserial, gpiozero (installed), smbus2 (installed)
#
# Default pin mapping (Dragino LoRa/GPS HAT typical):
#   LoRa SPI: /dev/spidev0.0 (CE0)
#   DIO0 = GPIO25 (RX done)
#   RST  = GPIO17
#   GPS  = /dev/serial0 9600-115200 (NMEA)
#
# For raw LoRa RX. Not LoRaWAN (no MAC/crypto).
#
# MQTT topics:
#   publish: lora/rx/raw
#   payload JSON includes: hex/base64 payload, rssi, snr, freq_hz, sf, bw, timestamp, gps (when available).

import os
import time
import json
import base64
import signal
import threading
from datetime import datetime, timezone
from typing import Optional, Tuple

import spidev
import RPi.GPIO as GPIO
import serial
from paho.mqtt.client import Client as MQTTClient

# --------------------
# Configuration (env)
# --------------------
LORA_FREQ_HZ = int(os.getenv("LORA_FREQ_HZ", "868100000"))   # 868.1 MHz default (EU868). Use 915000000 for US915.
LORA_SF = int(os.getenv("LORA_SF", "7"))                     # 7..12
LORA_BW_KHZ = int(os.getenv("LORA_BW_KHZ", "125"))           # 125, 250, 500
LORA_CR = os.getenv("LORA_CR", "4/5")                        # 4/5, 4/6, 4/7, 4/8
LORA_CRC_ON = os.getenv("LORA_CRC_ON", "1") == "1"           # enable CRC expectation
LORA_PREAMBLE = int(os.getenv("LORA_PREAMBLE", "8"))         # symbols

PIN_DIO0 = int(os.getenv("PIN_DIO0", "25"))
PIN_RST = int(os.getenv("PIN_RST", "17"))

SPI_BUS = int(os.getenv("SPI_BUS", "0"))
SPI_DEV = int(os.getenv("SPI_DEV", "0"))
SPI_MAX_HZ = int(os.getenv("SPI_MAX_HZ", "8000000"))  # 8 MHz safe

MQTT_HOST = os.getenv("MQTT_HOST", "localhost")
MQTT_PORT = int(os.getenv("MQTT_PORT", "1883"))
MQTT_USERNAME = os.getenv("MQTT_USERNAME", "")
MQTT_PASSWORD = os.getenv("MQTT_PASSWORD", "")
MQTT_TOPIC = os.getenv("MQTT_TOPIC", "lora/rx/raw")
MQTT_CLIENT_ID = os.getenv("MQTT_CLIENT_ID", "rpi-zero2w-lora-bridge")
MQTT_KEEPALIVE = int(os.getenv("MQTT_KEEPALIVE", "30"))
MQTT_TLS = os.getenv("MQTT_TLS", "0") == "1"

GPS_ENABLE = os.getenv("GPS_ENABLE", "1") == "1"
GPS_PORT = os.getenv("GPS_PORT", "/dev/serial0")
GPS_BAUD = int(os.getenv("GPS_BAUD", "9600"))

TEST_PAYLOAD = os.getenv("TEST_PAYLOAD", "")  # If set, inject into MQTT and exit

# SX127x registers
REG_FIFO = 0x00
REG_OP_MODE = 0x01
REG_FRF_MSB = 0x06
REG_FRF_MID = 0x07
REG_FRF_LSB = 0x08
REG_PA_CONFIG = 0x09
REG_LNA = 0x0C
REG_FIFO_ADDR_PTR = 0x0D
REG_FIFO_TX_BASE_ADDR = 0x0E
REG_FIFO_RX_BASE_ADDR = 0x0F
REG_FIFO_RX_CURRENT_ADDR = 0x10
REG_IRQ_FLAGS_MASK = 0x11
REG_IRQ_FLAGS = 0x12
REG_RX_NB_BYTES = 0x13
REG_PKT_SNR_VALUE = 0x19
REG_PKT_RSSI_VALUE = 0x1A
REG_MODEM_CONFIG_1 = 0x1D
REG_MODEM_CONFIG_2 = 0x1E
REG_SYMB_TIMEOUT_LSB = 0x1F
REG_PREAMBLE_MSB = 0x20
REG_PREAMBLE_LSB = 0x21
REG_PAYLOAD_LENGTH = 0x22
REG_MODEM_CONFIG_3 = 0x26
REG_DIO_MAPPING_1 = 0x40
REG_VERSION = 0x42

# OpMode bits
LONG_RANGE_MODE = 0x80  # LoRa
MODE_SLEEP = 0x00
MODE_STDBY = 0x01
MODE_RXCONT = 0x05

# Band threshold: HF port above 525MHz
HF_PORT = True

class SX127x:
    def __init__(self, spi_bus, spi_dev, max_hz, pin_dio0, pin_rst):
        self.spi = spidev.SpiDev()
        self.spi.open(spi_bus, spi_dev)
        self.spi.max_speed_hz = max_hz
        self.spi.mode = 0

        self.pin_dio0 = pin_dio0
        self.pin_rst = pin_rst

        GPIO.setmode(GPIO.BCM)
        GPIO.setup(self.pin_rst, GPIO.OUT, initial=GPIO.HIGH)
        GPIO.setup(self.pin_dio0, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

        self.rx_callback = None
        self.lock = threading.Lock()

    def close(self):
        try:
            self.spi.close()
        except Exception:
            pass
        GPIO.cleanup()

    def _write_reg(self, addr, val):
        # bit7=1 for write
        self.spi.xfer2([addr | 0x80, val & 0xFF])

    def _read_reg(self, addr):
        # bit7=0 for read
        return self.spi.xfer2([addr & 0x7F, 0x00])[1]

    def _burst_read(self, addr, length):
        # read 'length' bytes from 'addr'
        resp = self.spi.xfer2([addr & 0x7F] + [0x00] * length)
        return resp[1:]

    def _burst_write(self, addr, data):
        self.spi.xfer2([addr | 0x80] + list(data))

    def reset(self):
        # Hardware reset: drive low, then high
        GPIO.output(self.pin_rst, GPIO.LOW)
        time.sleep(0.01)
        GPIO.output(self.pin_rst, GPIO.HIGH)
        time.sleep(0.01)

    def set_mode(self, mode_bits):
        self._write_reg(REG_OP_MODE, LONG_RANGE_MODE | mode_bits)

    def init_lora(self, freq_hz, sf, bw_khz, cr, crc_on, preamble):
        # Reset & check version
        self.reset()
        time.sleep(0.01)
        ver = self._read_reg(REG_VERSION)
        if ver == 0x00 or ver == 0xFF:
            raise RuntimeError("SX127x not responding on SPI (REG_VERSION read as 0x%02X)" % ver)

        # Sleep LoRa
        self.set_mode(MODE_SLEEP)
        time.sleep(0.01)

        # Frequency
        frf = int(freq_hz / (32e6 / (1 << 19)))
        self._write_reg(REG_FRF_MSB, (frf >> 16) & 0xFF)
        self._write_reg(REG_FRF_MID, (frf >> 8) & 0xFF)
        self._write_reg(REG_FRF_LSB, frf & 0xFF)

        # LNA: max gain, boost on
        self._write_reg(REG_LNA, 0x23)  # 0b0010_0011

        # BW
        bw_map = {125: 0x70, 250: 0x80, 500: 0x90}
        if bw_khz not in bw_map:
            raise ValueError("Unsupported BW kHz: %s" % bw_khz)
        bw_bits = bw_map[bw_khz]

        # Coding rate
        cr_map = {"4/5": 0x02, "4/6": 0x04, "4/7": 0x06, "4/8": 0x08}
        if cr not in cr_map:
            raise ValueError("Unsupported CR: %s" % cr)
        cr_bits = cr_map[cr]

        # Explicit header mode
        modem_config_1 = bw_bits | cr_bits | 0x00
        self._write_reg(REG_MODEM_CONFIG_1, modem_config_1)

        # SF
        if sf < 6 or sf > 12:
            raise ValueError("SF must be 6..12")
        sf_bits = (sf << 4) & 0xF0

        # CRC on?
        crc_bits = 0x04 if crc_on else 0x00
        modem_config_2 = sf_bits | crc_bits | 0x03  # SymbTimeout MSB2 bits as 0b11 default
        self._write_reg(REG_MODEM_CONFIG_2, modem_config_2)

        # Modem config 3: LowDataRateOptimize if SF11/12 at low BW; AGC on
        ldo = 0x08 if (bw_khz == 125 and sf >= 11) else 0x00
        self._write_reg(REG_MODEM_CONFIG_3, ldo | 0x04)

        # Preamble
        self._write_reg(REG_PREAMBLE_MSB, (preamble >> 8) & 0xFF)
        self._write_reg(REG_PREAMBLE_LSB, preamble & 0xFF)

        # Set FIFO base addresses
        self._write_reg(REG_FIFO_RX_BASE_ADDR, 0x00)
        self._write_reg(REG_FIFO_TX_BASE_ADDR, 0x80)
        self._write_reg(REG_PAYLOAD_LENGTH, 0xFF)  # allow full 255

        # IRQ: unmask RxDone, RxTimeout, ValidHeader, CRCError
        irq_mask = 0x00  # we’ll handle in flags
        self._write_reg(REG_IRQ_FLAGS_MASK, irq_mask)

        # Map DIO0 to RxDone (00)
        self._write_reg(REG_DIO_MAPPING_1, 0x00)

        # Standby then RX continuous
        self.set_mode(MODE_STDBY)
        time.sleep(0.01)
        self._clear_irq()
        self.set_mode(MODE_RXCONT)

    def _clear_irq(self):
        self._write_reg(REG_IRQ_FLAGS, 0xFF)

    def _read_packet(self) -> Optional[dict]:
        # Called when DIO0 indicates RxDone
        irq = self._read_reg(REG_IRQ_FLAGS)
        # Save then clear
        self._clear_irq()

        if irq & 0x20:  # CRC Error
            return None
        if irq & 0x40 == 0x00:  # RxDone not set
            return None

        # Read FIFO
        current_addr = self._read_reg(REG_FIFO_RX_CURRENT_ADDR)
        nb = self._read_reg(REG_RX_NB_BYTES)
        self._write_reg(REG_FIFO_ADDR_PTR, current_addr)
        data = self._burst_read(REG_FIFO, nb)

        # SNR and RSSI
        raw_snr = self._read_reg(REG_PKT_SNR_VALUE)
        snr = (raw_snr if raw_snr < 128 else raw_snr - 256) / 4.0
        raw_rssi = self._read_reg(REG_PKT_RSSI_VALUE)
        rssi = raw_rssi - (157 if HF_PORT else 164)

        return {
            "payload_bytes": bytes(data),
            "rssi": rssi,
            "snr": snr,
            "num_bytes": nb,
        }

    def on_dio0(self, channel):
        # ISR -> schedule processing in a thread
        if self.rx_callback:
            try:
                with self.lock:
                    pkt = self._read_packet()
                if pkt:
                    self.rx_callback(pkt)
            except Exception as e:
                print(f"[DIO0 handler] Error: {e}")

    def start_rx(self, rx_callback):
        self.rx_callback = rx_callback
        GPIO.add_event_detect(self.pin_dio0, GPIO.RISING, callback=self.on_dio0, bouncetime=1)


class GPSReader(threading.Thread):
    def __init__(self, port, baud):
        super().__init__(daemon=True)
        self.port = port
        self.baud = baud
        self.latest = None  # (lat, lon, fix_time_iso) or None
        self._stop = threading.Event()
        self.ser = None

    def run(self):
        try:
            self.ser = serial.Serial(self.port, self.baud, timeout=1)
        except Exception as e:
            print(f"[GPS] Unable to open {self.port}: {e}")
            return
        while not self._stop.is_set():
            try:
                line = self.ser.readline().decode(errors="ignore").strip()
                if line.startswith("$GPRMC") or line.startswith("$GNRMC"):
                    latlon, ts = self._parse_rmc(line)
                    if latlon:
                        self.latest = (latlon[0], latlon[1], ts)
            except Exception:
                pass
        try:
            self.ser.close()
        except Exception:
            pass

    def stop(self):
        self._stop.set()

    @staticmethod
    def _nmea_to_deg(val, hemi):
        # NMEA ddmm.mmmm or dddmm.mmmm
        if not val or val == "":
            return None
        parts = val.split(".")
        if len(parts) != 2:
            return None
        head = parts[0]
        mins = float(head[-2:] + "." + parts[1])
        deg = int(head[:-2]) if head[:-2] else 0
        coord = deg + mins / 60.0
        if hemi in ("S", "W"):
            coord = -coord
        return coord

    def _parse_rmc(self, line):
        # $GPRMC,hhmmss.sss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,ddmmyy,x.x,a*hh
        f = line.split(",")
        if len(f) < 12:
            return None, None
        status = f[2]
        if status != "A":
            return None, None
        utc = f[1]
        lat, latH = f[3], f[4]
        lon, lonH = f[5], f[6]
        date = f[9]

        lat_deg = self._nmea_to_deg(lat, latH)
        lon_deg = self._nmea_to_deg(lon, lonH)
        if lat_deg is None or lon_deg is None:
            return None, None

        # Build ISO timestamp (UTC). If parsing fails, use now().
        try:
            hh = int(utc[0:2]); mm = int(utc[2:4]); ss = int(utc[4:6])
            dd = int(date[0:2]); mo = int(date[2:4]); yy = int(date[4:6]) + 2000
            dt = datetime(yy, mo, dd, hh, mm, ss, tzinfo=timezone.utc).isoformat()
        except Exception:
            dt = datetime.now(timezone.utc).isoformat()

        return (lat_deg, lon_deg), dt


class MQTTBridge:
    def __init__(self, host, port, username, password, client_id, keepalive, tls):
        self.client = MQTTClient(client_id=client_id, clean_session=True)
        if username:
            self.client.username_pw_set(username, password or None)
        if tls:
            import ssl
            self.client.tls_set(cert_reqs=ssl.CERT_NONE)
            self.client.tls_insecure_set(True)
        self.host = host
        self.port = port
        self.keepalive = keepalive
        self.connected = False
        self.client.on_connect = self._on_connect
        self.client.on_disconnect = self._on_disconnect

    def _on_connect(self, client, userdata, flags, rc):
        self.connected = (rc == 0)
        print(f"[MQTT] Connected rc={rc}")

    def _on_disconnect(self, client, userdata, rc):
        self.connected = False
        print(f"[MQTT] Disconnected rc={rc}")

    def connect(self):
        self.client.connect(self.host, self.port, self.keepalive)
        self.client.loop_start()

    def publish_json(self, topic, obj, qos=0, retain=False):
        payload = json.dumps(obj, separators=(",", ":"), ensure_ascii=False)
        res = self.client.publish(topic, payload, qos=qos, retain=retain)
        if res.rc != 0:
            print(f"[MQTT] publish rc={res.rc}")
        return res


def main():
    # Test mode (no radio access needed): inject an example payload into MQTT and exit
    if TEST_PAYLOAD:
        mqtt = MQTTBridge(MQTT_HOST, MQTT_PORT, MQTT_USERNAME, MQTT_PASSWORD, MQTT_CLIENT_ID, MQTT_KEEPALIVE, MQTT_TLS)
        mqtt.connect()
        time.sleep(1)
        doc = {
            "ts": datetime.now(timezone.utc).isoformat(),
            "freq_hz": LORA_FREQ_HZ,
            "sf": LORA_SF,
            "bw_khz": LORA_BW_KHZ,
            "rssi": None,
            "snr": None,
            "payload_hex": TEST_PAYLOAD.encode().hex(),
            "payload_b64": base64.b64encode(TEST_PAYLOAD.encode()).decode(),
            "note": "injected-test-payload",
        }
        mqtt.publish_json(MQTT_TOPIC, doc)
        time.sleep(0.5)
        return

    lora = SX127x(SPI_BUS, SPI_DEV, SPI_MAX_HZ, PIN_DIO0, PIN_RST)
    gps = GPSReader(GPS_PORT, GPS_BAUD) if GPS_ENABLE else None
    mqtt = MQTTBridge(MQTT_HOST, MQTT_PORT, MQTT_USERNAME, MQTT_PASSWORD, MQTT_CLIENT_ID, MQTT_KEEPALIVE, MQTT_TLS)

    def cleanup(*_):
        print("Shutting down...")
        try:
            if gps:
                gps.stop()
        except Exception:
            pass
        try:
            lora.close()
        except Exception:
            pass
        mqtt.client.loop_stop()
        exit(0)

    signal.signal(signal.SIGINT, cleanup)
    signal.signal(signal.SIGTERM, cleanup)

    mqtt.connect()
    if gps:
        gps.start()

    # Initialize radio
    print("[LoRa] Initializing SX127x...")
    lora.init_lora(LORA_FREQ_HZ, LORA_SF, LORA_BW_KHZ, LORA_CR, LORA_CRC_ON, LORA_PREAMBLE)

    # Small print to confirm chip version
    ver = lora._read_reg(REG_VERSION)
    print(f"[LoRa] SX127x REG_VERSION=0x{ver:02X} (expect 0x12 for SX1276)")

    def on_packet(pkt):
        # Prepare JSON document
        now = datetime.now(timezone.utc).isoformat()
        gps_doc = None
        if gps and gps.latest:
            lat, lon, gts = gps.latest
            gps_doc = {"lat": lat, "lon": lon, "ts": gts}

        payload_bytes = pkt["payload_bytes"]
        doc = {
            "ts": now,
            "freq_hz": LORA_FREQ_HZ,
            "sf": LORA_SF,
            "bw_khz": LORA_BW_KHZ,
            "rssi": pkt["rssi"],
            "snr": pkt["snr"],
            "len": pkt["num_bytes"],
            "payload_hex": payload_bytes.hex(),
            "payload_b64": base64.b64encode(payload_bytes).decode(),
            "gps": gps_doc,
        }
        mqtt.publish_json(MQTT_TOPIC, doc)

        # Optional console log preview (hex)
        print(f"[LoRa] RX len={pkt['num_bytes']} RSSI={pkt['rssi']:.1f}dBm SNR={pkt['snr']:.1f} dB")

    lora.start_rx(on_packet)

    print("[LoRa] RX continuous. Waiting for packets...")
    print(f"[MQTT] Publishing to mqtt://{MQTT_HOST}:{MQTT_PORT} topic '{MQTT_TOPIC}'")
    if gps:
        print(f"[GPS] Reading NMEA from {GPS_PORT} @ {GPS_BAUD} baud")

    # Idle forever
    while True:
        time.sleep(1)


if __name__ == "__main__":
    main()

---

Build/Flash/Run commands

We’re not flashing microcontroller firmware; instead we will set up a Python virtual environment, install dependencies, and run the script. This section uses Bookworm 64-bit and Python 3.11.

1) Create project and venv

mkdir -p ~/lora-mqtt-bridge
cd ~/lora-mqtt-bridge

python3 --version
# Expect Python 3.11.x

python3 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip wheel setuptools

2) Install OS-level prerequisites

sudo apt update
sudo apt install -y python3-dev python3-venv python3-rpi.gpio \
    python3-serial python3-spidev \
    mosquitto mosquitto-clients minicom

Note:
– We install mosquitto to run a local broker; if you use a remote broker, you can skip mosquitto.
– minicom is used for optional GPS validation.

3) Install Python packages in the venv

pip install spidev RPi.GPIO paho-mqtt pyserial gpiozero smbus2

Optional: pin versions via a requirements.txt:

cat > requirements.txt <<'EOF'
spidev>=3.6
RPi.GPIO>=0.7.1
paho-mqtt>=1.6.1
pyserial>=3.5
gpiozero>=1.6.2
smbus2>=0.4.3
EOF

pip install -r requirements.txt

4) Place the code

nano ~/lora-mqtt-bridge/bridge.py
# paste the Full Code content and save
chmod +x ~/lora-mqtt-bridge/bridge.py

5) First run (with environment defaults)

If you’re in EU868, the defaults are already set to 868.1 MHz, SF7, BW125. To run with defaults:

cd ~/lora-mqtt-bridge
source .venv/bin/activate
./bridge.py

If you’re in US915:

export LORA_FREQ_HZ=915000000
export LORA_SF=7
export LORA_BW_KHZ=125
./bridge.py

To point the gateway to a remote MQTT broker:

export MQTT_HOST="your-broker.example.com"
export MQTT_PORT=8883
export MQTT_TLS=1
export MQTT_USERNAME="user"
export MQTT_PASSWORD="pass"
./bridge.py

To run a simple broker on the Pi:

sudo systemctl enable --now mosquitto

6) Optional: systemd service for autostart

Create a service unit:

sudo tee /etc/systemd/system/lora-mqtt-bridge.service >/dev/null <<'EOF'
[Unit]
Description=LoRa to MQTT Bridge (Raspberry Pi Zero 2 W + Dragino LoRa/GPS HAT)
After=network-online.target mosquitto.service
Wants=network-online.target

[Service]
Type=simple
User=pi
WorkingDirectory=/home/pi/lora-mqtt-bridge
Environment=PYTHONUNBUFFERED=1
Environment=LORA_FREQ_HZ=868100000
Environment=LORA_SF=7
Environment=LORA_BW_KHZ=125
Environment=LORA_CR=4/5
Environment=LORA_CRC_ON=1
Environment=LORA_PREAMBLE=8
Environment=PIN_DIO0=25
Environment=PIN_RST=17
Environment=MQTT_HOST=localhost
Environment=MQTT_PORT=1883
Environment=MQTT_TOPIC=lora/rx/raw
Environment=MQTT_CLIENT_ID=rpi-zero2w-lora-bridge
Environment=GPS_ENABLE=1
Environment=GPS_PORT=/dev/serial0
Environment=GPS_BAUD=9600
ExecStart=/home/pi/lora-mqtt-bridge/.venv/bin/python /home/pi/lora-mqtt-bridge/bridge.py
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl daemon-reload
sudo systemctl enable --now lora-mqtt-bridge.service

Check status:

systemctl status lora-mqtt-bridge.service -n 50
journalctl -u lora-mqtt-bridge.service -f

---

Step-by-step Validation

This section validates each layer from bottom (hardware) to top (MQTT messages). Follow in order.

1) Validate SPI device and radio presence

• Check that /dev/spidev0.0 exists:

ls -l /dev/spidev0.0

• Read the SX127x version register via the script log. Start the app:

cd ~/lora-mqtt-bridge
source .venv/bin/activate
./bridge.py

Look for:

• “[LoRa] SX127x REG_VERSION=0x12” — 0x12 indicates SX1276/77/78 family.
• If you see 0x00 or 0xFF, the radio is not responding. Recheck SPI enable and pin seating.

2) Validate UART/GPS (optional but recommended)

• Connect to GPS at 9600 baud:

sudo minicom -b 9600 -D /dev/serial0

You should see NMEA sentences like $GPRMC/$GNRMC. Exit minicom with Ctrl-A, X. If you get no data, ensure dtoverlay=disable-bt is set in /boot/firmware/config.txt and that the serial console is disabled in cmdline.txt, then reboot.

When the script runs, you should occasionally see gps entries in the published JSON once a fix is obtained.

3) Validate MQTT connectivity

• If using local mosquitto, ensure it’s active:

sudo systemctl status mosquitto

• Subscribe to the topic:

mosquitto_sub -h localhost -t 'lora/rx/raw' -v

Keep this subscriber running in a second terminal.

• Without a LoRa transmitter, test the MQTT path with injection:

cd ~/lora-mqtt-bridge
source .venv/bin/activate
export TEST_PAYLOAD="hello-from-bridge"
./bridge.py

You should see a JSON message on the subscriber with payload_hex and payload_b64 fields and note “injected-test-payload”.

4) Validate DIO0 interrupt and RX behavior

Even without a transmitter, the radio should toggle IRQ flags on RX timeouts. In the main run (not test mode), look for:

• “[LoRa] RX continuous. Waiting for packets…”

If you have a second LoRa transmitter (recommended):

• Configure it to the same parameters:
• Frequency: match LORA_FREQ_HZ (e.g., 868.1 MHz)
• BW: 125 kHz
• SF: 7
• CR: 4/5
• CRC: on (optional, match the bridge)
• Send a short payload (e.g., “PING”).
• You should see a console line:
• “RX len=4 RSSI=-xx.xdBm SNR=yy.y dB”
• On the MQTT subscriber, you will receive a JSON document. Example:

lora/rx/raw {"ts":"2025-11-01T12:34:56.789012+00:00","freq_hz":868100000,"sf":7,"bw_khz":125,"rssi":-92.5,"snr":8.0,"len":4,"payload_hex":"50494e47","payload_b64":"UElORw==","gps":{"lat":52.52001,"lon":13.40495,"ts":"2025-11-01T12:34:55+00:00"}}

5) Validate resilience

• Stop and start mosquitto while the script is running; the bridge should reconnect automatically within the keepalive window.
• Unplug/replug the GPS UART or temporarily disable GPS_ENABLE to confirm the bridge still functions for LoRa-only RX.

---

Troubleshooting

• No /dev/spidev0.0:
• Ensure SPI is enabled: sudo raspi-config nonint do_spi 0
• Check /boot/firmware/config.txt has dtparam=spi=on

• Reboot after enabling SPI.

• SX127x REG_VERSION reads 0x00 or 0xFF:

• HAT not fully seated or wrong chip select. This project expects CE0 => /dev/spidev0.0.
• Confirm your pin mapping; DIO0/RST won’t affect REG_VERSION, but CS must be CE0 (GPIO8).

• Verify power: The HAT requires 3.3 V and 5 V per design; use a stable supply.

• “GPIO permission denied” or “module not found”:

• Ensure you’re running from the venv and that RPi.GPIO is installed: pip show RPi.GPIO.

• Run the script as a user with GPIO access (pi). If using systemd, our unit sets User=pi.

• DIO0 interrupt not firing:

• Confirm PIN_DIO0=25 matches your HAT. Some variants may wire DIO0 differently; check the PCB silkscreen or vendor schematic.
• Try polling (as a temporary debug) by calling _read_packet() in a loop if interrupts prove unreliable.

• Ensure you’re in RX continuous: the console should show “RX continuous. Waiting for packets…”.

• MQTT publish errors:

• Check broker reachability: mosquitto_pub -h <host> -t test -m hi

• For TLS: set MQTT_TLS=1 and ensure port is correct (often 8883). If you have CA certs, configure client.tls_set(ca_certs=...) in code.

• GPS shows no data:

• Verify /dev/serial0 points to PL011 and isn’t attached to the console or Bluetooth: ensure dtoverlay=disable-bt and console removed from /boot/firmware/cmdline.txt; reboot.

• Try different baud rates if your HAT’s GPS is configured differently (some use 9600, others 115200).

• Wrong band or poor reception:

• Verify antenna is for the correct band (868 vs 915 MHz).
• Check RSSI/SNR numbers. SNR near or above 0 dB typically yields solid demodulation; negative SNR (down to about −20 dB) can still work.

---

Improvements

• Protocol: Add a payload decoder or framing (CBOR/JSON/SLIP) to identify device IDs and sensor types; currently, the gateway publishes raw bytes.
• Security: Enable authenticated MQTT with TLS and client certificates; consider ACLs to restrict topics.
• Observability: Add Prometheus metrics (packet counts, RSSI histogram), log rotation, and health checks.
• Backpressure: Implement an internal queue with bounded size and asynchronous publishing to avoid blocking ISR.
• Resilience: Auto-reinitialize the SX127x on repeated CRC errors or timeouts; add a watchdog timer.
• GPS: Emit GPS-only heartbeat messages to indicate gateway position and availability; filter NMEA for fix state and HDOP.
• Packaging: Convert to a Python package and install via setuptools; include a systemd EnvironmentFile for cleaner configuration.
• Multi-region config: Provide a static config file that sets frequency plans per region and enforces legal duty cycle constraints for TX (if you later add transmit capabilities).
• LoRaWAN: To handle LoRaWAN packets properly, you need a Semtech concentrator (e.g., SX130x) and a packet forwarder; the SX127x is a single-channel radio not suited for compliant LoRaWAN gateways. For simple, private, single-channel experiments, you can still parse and forward raw LoRaWAN frames to MQTT for offline analysis.

---

Final Checklist

• Raspberry Pi OS Bookworm 64-bit installed and updated
• SPI enabled, UART enabled, Bluetooth disabled for GPS: checked /boot/firmware/config.txt and cmdline.txt
• Dragino LoRa/GPS HAT seated and antenna attached
• Python venv created; packages installed: spidev, RPi.GPIO, paho-mqtt, pyserial, gpiozero, smbus2
• bridge.py placed at ~/lora-mqtt-bridge/ and made executable
• Service optional: lora-mqtt-bridge.service installed, enabled, and running
• Validation:
• REG_VERSION reads 0x12
• Serial NMEA visible via minicom (optional)
• mosquitto running or reachable broker configured
• TEST_PAYLOAD injection confirmed on MQTT subscriber
• Real LoRa packet received and published with RSSI/SNR metadata
• Troubleshooting notes at hand for SPI, UART, DIO0, MQTT issues

With this setup, your Raspberry Pi Zero 2 W + Dragino LoRa/GPS HAT operates as a compact, flexible LoRa-to-MQTT gateway bridge, ready to feed downstream systems like Node-RED, InfluxDB, or cloud IoT platforms.

Objetivo y caso de uso

Qué construirás: Un detector de palabras clave utilizando Raspberry Pi Pico W y el micrófono INMP441 para la captura de audio y la detección de comandos específicos.

Para qué sirve

• Control de dispositivos IoT mediante comandos de voz en entornos domésticos.
• Activación de asistentes virtuales en aplicaciones de automatización.
• Implementación de sistemas de seguridad que responden a palabras clave predefinidas.
• Desarrollo de interfaces de usuario accesibles para personas con discapacidades.

Resultado esperado

• Detección de palabras clave con una latencia menor a 200 ms.
• Precisión de detección superior al 90% en condiciones de ruido controlado.
• Capacidad de procesar hasta 5 comandos por segundo.
• Consumo de energía inferior a 100 mW durante la operación activa.

Público objetivo: Desarrolladores de software y hardware; Nivel: Alto

Arquitectura/flujo: Captura de audio mediante INMP441, procesamiento en Raspberry Pi Pico W, detección de palabras clave y respuesta a eventos.

Nivel: alto

Prerrequisitos

Sistema operativo y entorno de trabajo

• Host de desarrollo: Raspberry Pi OS Bookworm 64-bit
• Imagen estable Bookworm de 64 bits (kernel 6.x), instalada en una Raspberry Pi (4/400/5).
• Python del sistema: Python 3.11 (3.11.2 en Bookworm).
• Acceso a terminal con privilegios sudo y conexión a Internet.

Toolchain exacta (versiones probadas)

• cmake 3.25.1 (paquete Debian: 3.25.1-1)
• ninja-build 1.11.1 (paquete Debian: 1.11.1-1)
• gcc-arm-none-eabi 10.3-2021.10 (paquete Debian: 15:10.3-2021.10+rpi1)
• libnewlib-arm-none-eabi 4.1.0-202202 (paquete Debian: 4.1.0.202202-1+rpi1)
• git 2.39.2 (o superior en Bookworm)
• picotool 1.1.2 (paquete Debian: 1.1.2-1)
• Raspberry Pi Pico SDK v2.0.0 (tag oficial)
• pico-extras v2.0.0 (para entorno PIO auxiliar, aunque en este caso no usaremos libs de i2s de salida)
• Thonny (opcional, no requerido)
• pyserial 3.5 (en venv de Python 3.11 para monitorización por USB CDC)

Verifica las versiones instaladas (opcional):
– cmake –version → 3.25.1
– ninja –version → 1.11.1
– arm-none-eabi-gcc –version → 10.3-2021.10
– picotool version → 1.1.2

Habilitar interfaces y ajustes del sistema (host)

Aunque programaremos la Raspberry Pi Pico W (RP2040) por USB y no usamos buses GPIO del host, conviene:
1) Deshabilitar consola serie sobre UART GPIO (evita conflictos si más adelante usas UART):
– sudo raspi-config
– Interface Options → Serial Port → Login shell over serial? No → Enable serial port hardware? Yes
– Reboot si lo pide.

2) Añadir el usuario al grupo dialout para acceso a puertos serie (USB CDC):
– sudo usermod -aG dialout $USER
– Cierra sesión y vuelve a entrar.

3) Crear un entorno virtual de Python 3.11 para herramientas auxiliares (monitor serie, validación):
– python3 -m venv ~/venvs/pico-kws
– source ~/venvs/pico-kws/bin/activate
– pip install –upgrade pip==23.2.1
– pip install pyserial==3.5

4) Instalar toolchain y utilidades:
– sudo apt update
– sudo apt install -y git cmake ninja-build gcc-arm-none-eabi libnewlib-arm-none-eabi picotool

Materiales

• 1 × Raspberry Pi Pico W (RP2040, con Wi‑Fi; usaremos USB para programar y CDC para logs).
• 1 × Módulo de micrófono digital INMP441 I2S (pines: VDD, GND, SCK/BCLK, WS/LRCLK, SD, L/R).
• 1 × Cable micro‑USB de datos (no solo carga).
• 1 × Protoboard y 6–7 cables dupont macho‑macho.
• 1 × Condensador de desacoplo 100 nF cerámico (entre VDD y GND del micrófono, recomendado).
• 1 × Raspberry Pi (host) con Raspberry Pi OS Bookworm 64‑bit (para compilar y flashear).
• Opcional: Cinta adhesiva/soporte para fijar micrófono y reducir vibraciones.

Modelo exacto del dispositivo usado en este caso práctico: Raspberry Pi Pico W + INMP441 I2S Mic.

Preparación y conexión

Consideraciones eléctricas

• El INMP441 funciona a 3.3 V. No alimentes a 5 V.
• Añade un condensador de 100 nF entre VDD y GND lo más cerca posible del micrófono.
• El pin L/R define el canal que entrega por SD. Conéctalo a GND para canal izquierdo (L).

Mapeo de pines y cableado

Usaremos la PIO del RP2040 para recibir I2S. Asignaremos:
– BCLK (SCK) en GPIO10
– LRCLK (WS) en GPIO11
– SD (DOUT) en GPIO12
– L/R a GND para seleccionar el canal izquierdo
– VDD a 3V3(OUT)
– GND a GND

Tabla de conexiones (Pico W vs INMP441):

Notas:
– El INMP441 no requiere MCLK externo.
– Mantén cortos los cables de BCLK/LRCLK/SD; cruza GND cerca para retorno.

Código completo

Objetivo: i2s-keyword-spotting-pico. Implementaremos:
– PIO para capturar I2S (solo canal izquierdo).
– Extracción de energía por tramas de 10 ms.
– Detección por correlación normalizada con una plantilla de “hola” (plantilla de ejemplo incluida).
– Señalización por LED y logs por USB CDC.

Estructura mínima del proyecto:
– i2s-keyword-spotting-pico/
– CMakeLists.txt
– i2s_rx.pio
– src/
– main.cpp
– tools/
– monitor.py

CMakeLists.txt

cmake_minimum_required(VERSION 3.25)
include($ENV{PICO_SDK_PATH}/external/pico_sdk_import.cmake)

project(i2s_keyword_spotting_pico C CXX ASM)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)

pico_sdk_init()

add_executable(i2s_keyword_spotting_pico
    src/main.cpp
    i2s_rx.pio
)

pico_generate_pio_header(i2s_keyword_spotting_pico ${CMAKE_CURRENT_LIST_DIR}/i2s_rx.pio)

target_link_libraries(i2s_keyword_spotting_pico
    pico_stdlib
    hardware_pio
    hardware_gpio
    hardware_clocks
)

pico_enable_stdio_usb(i2s_keyword_spotting_pico 1)
pico_enable_stdio_uart(i2s_keyword_spotting_pico 0)

pico_add_extra_outputs(i2s_keyword_spotting_pico)

i2s_rx.pio

PIO para recibir 32 bits por muestra del canal izquierdo sincronizados por BCLK, usando LRCLK como estrobado de canal. Leemos SD en cada flanco de subida de BCLK cuando LRCLK está bajo (izquierda). Ignoramos el canal derecho.

.program i2s_rx
; Configuración:
; - 'in' pins base = SD (dato del micrófono)
; - Usamos WAIT sobre GPIO absolutos para LRCLK y BCLK
; Convención:
; - LRCLK bajo = canal izquierdo
; - 32 bits por muestra (el INMP441 emite 24 bits MSB justificados; alineamos a 32 y luego recortamos en C++)

; Reemplaza estos números si cambias el cableado
%define BCLK_GPIO 10
%define LRCLK_GPIO 11

.wrap_target
    ; Espera a inicio de trama de canal izquierdo (LRCLK = 0)
    wait 0 gpio LRCLK_GPIO
    ; Alinea a flanco bajo de BCLK antes de empezar
    wait 0 gpio BCLK_GPIO

    set x, 31          ; 32 bits
bitloop_left:
    ; Espera flanco de subida de BCLK, muestrea SD
    wait 1 gpio BCLK_GPIO
    in pins, 1
    ; Espera flanco de bajada de BCLK para el siguiente bit
    wait 0 gpio BCLK_GPIO
    jmp x-- bitloop_left

    ; Empuja los 32 bits del canal izquierdo
    push block

    ; Consumir canal derecho (32 ciclos) sin empujar
    ; Espera que LRCLK sea 1 (canal derecho)
    wait 1 gpio LRCLK_GPIO
    set x, 31
bitloop_right:
    wait 1 gpio BCLK_GPIO
    nop
    wait 0 gpio BCLK_GPIO
    jmp x-- bitloop_right

    jmp .wrap_target
.wrap

src/main.cpp

Código principal: inicializa PIO, lee muestras, calcula energía por tramas de 10 ms a 16 kHz, compara con plantilla y emite detecciones.

#include <cstdio>
#include <cmath>
#include "pico/stdlib.h"
#include "hardware/pio.h"
#include "hardware/gpio.h"
#include "hardware/clocks.h"
#include "i2s_rx.pio.h"

static constexpr uint GPIO_BCLK = 10;
static constexpr uint GPIO_LRCLK = 11;
static constexpr uint GPIO_SD = 12;

static constexpr uint LED_PIN = PICO_DEFAULT_LED_PIN;

// Muestreo y DSP
static constexpr float SAMPLE_RATE = 16000.0f;    // Hz
static constexpr int FRAME_SAMPLES = 160;         // 10 ms a 16 kHz
static constexpr int FEAT_FRAMES = 50;            // 0.5 s de ventana para correlación
static constexpr float DETECT_COOLDOWN_S = 1.0f;
static constexpr float DETECT_THRESHOLD = 0.86f;

// Plantilla de energía (log-energía normalizada) para "hola" (50 frames, ~0.5 s).
// Esta plantilla es un ejemplo; puedes recalibrarla con tu voz para mayor robustez.
static float TEMPLATE_HOLA[FEAT_FRAMES] = {
    -0.57f,-0.40f,-0.22f, 0.05f, 0.33f, 0.62f, 0.81f, 0.93f, 0.75f, 0.40f,
    0.10f,-0.08f,-0.19f,-0.25f,-0.30f,-0.35f,-0.38f,-0.36f,-0.32f,-0.28f,
    -0.20f,-0.10f, 0.02f, 0.18f, 0.35f, 0.48f, 0.50f, 0.42f, 0.30f, 0.18f,
    0.06f,-0.05f,-0.15f,-0.22f,-0.26f,-0.28f,-0.29f,-0.28f,-0.26f,-0.23f,
    -0.19f,-0.15f,-0.11f,-0.07f,-0.05f,-0.04f,-0.05f,-0.08f,-0.12f,-0.16f
};

// Buffer circular de energía por frames
static float energy_ring[FEAT_FRAMES];
static int energy_idx = 0;
static bool ring_full = false;

// Filtro pasa-altos sencillo para quitar DC: y[n] = x[n] - x[n-1] + 0.995*y[n-1]
static inline int32_t hp_filter(int32_t x) {
    static int32_t x1 = 0;
    static float y1 = 0.0f;
    float y = (float)(x - x1) + 0.995f * y1;
    x1 = x;
    y1 = y;
    return (int32_t)y;
}

// Normaliza vector a media 0 y varianza 1
static void znormalize(float *v, int n) {
    float mean = 0.f, var = 0.f;
    for (int i = 0; i < n; ++i) mean += v[i];
    mean /= n;
    for (int i = 0; i < n; ++i) { float d = v[i] - mean; var += d*d; }
    var = (var / n);
    float stdv = (var > 1e-9f) ? sqrtf(var) : 1.0f;
    for (int i = 0; i < n; ++i) v[i] = (v[i] - mean) / stdv;
}

// Correlación normalizada coseno entre dos vectores ya normalizados
static float cosine_similarity(const float *a, const float *b, int n) {
    float dot = 0.f;
    for (int i = 0; i < n; ++i) dot += a[i]*b[i];
    return dot / (float)n;
}

// Convierte palabra de 32 bits I2S (MSB first) a muestra 16-bit
static inline int16_t i2s32_to_int16(uint32_t w) {
    // INMP441 entrega datos de 24 bits con signo, alineados a la izquierda dentro de 32 bits.
    // w: [S23..S0][pad 8 bits]. Desplazamos para obtener 16 bits significativos.
    int32_t s24 = (int32_t)(w) >> 8;     // 24 bits con signo en bits 31..8
    int16_t s16 = (int16_t)(s24 >> 8);   // Quita los 8 LSB -> 16-bit aproximado
    return s16;
}

int main() {
    stdio_init_all();
    sleep_ms(1500); // Espera a que el host abra el puerto USB

    // LED
    gpio_init(LED_PIN);
    gpio_set_dir(LED_PIN, true);
    gpio_put(LED_PIN, 0);

    // PIO setup
    PIO pio = pio0;
    uint sm = pio_claim_unused_sm(pio, true);
    uint offset = pio_add_program(pio, &i2s_rx_program);

    // Configurar pines
    gpio_pull_down(GPIO_BCLK);  // entradas, pero estabiliza
    gpio_pull_down(GPIO_LRCLK);
    gpio_pull_down(GPIO_SD);

    // Configurar PIO: base de 'in' en SD
    pio_sm_config c = i2s_rx_program_get_default_config(offset);
    sm_config_set_in_pins(&c, GPIO_SD);
    sm_config_set_in_shift(&c, true, true, 32); // shift right, autopush, threshold 32

    // Mapear set/out no usados, pero obligatorio setear pin base si fuera necesario
    // Velocidad: State machine corre al clock de sistema; usamos WAIT en GPIO (externos)
    float sys_clk_khz = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_SYS);
    (void)sys_clk_khz;

    // Inicializa el SM
    pio_sm_init(pio, sm, offset, &c);

    // Habilitar SM
    pio_sm_set_enabled(pio, sm, true);

    // Variables de DSP
    uint64_t last_detect_us = 0;
    uint32_t frame_count = 0;

    // Pre-normaliza la plantilla para correlación
    float tpl[FEAT_FRAMES];
    for (int i = 0; i < FEAT_FRAMES; ++i) tpl[i] = TEMPLATE_HOLA[i];
    znormalize(tpl, FEAT_FRAMES);

    // Bucle principal
    while (true) {
        // Leer FRAME_SAMPLES muestras de canal izquierdo
        int64_t energy_acc = 0;
        for (int i = 0; i < FRAME_SAMPLES; ++i) {
            // Bloquea hasta que haya una palabra en FIFO
            uint32_t w = pio_sm_get_blocking(pio, sm);
            int16_t s = i2s32_to_int16(w);
            int32_t hp = hp_filter(s);
            energy_acc += (int64_t)hp * (int64_t)hp;
        }

        // Energía log
        float e = logf((float)energy_acc + 1.0f);
        energy_ring[energy_idx] = e;
        energy_idx = (energy_idx + 1) % FEAT_FRAMES;
        if (energy_idx == 0) ring_full = true;

        frame_count++;

        // Cada frame ~10ms. Calcular correlación cuando la ventana está llena
        if (ring_full) {
            // Construye ventana ordenada
            float feat[FEAT_FRAMES];
            for (int i = 0; i < FEAT_FRAMES; ++i) {
                int idx = (energy_idx + i) % FEAT_FRAMES;
                feat[i] = energy_ring[idx];
            }
            znormalize(feat, FEAT_FRAMES);

            float score = cosine_similarity(feat, tpl, FEAT_FRAMES);

            // Cooldown
            uint64_t now = time_us_64();
            bool cooldown_ok = (now - last_detect_us) > (uint64_t)(DETECT_COOLDOWN_S * 1e6f);

            if (score >= DETECT_THRESHOLD && cooldown_ok) {
                last_detect_us = now;
                // Señaliza por LED y log
                gpio_put(LED_PIN, 1);
                printf("[KWS] DETECTADO: HOLA | score=%.3f | t=%.2fs\n", score, now / 1e6f);
            } else {
                gpio_put(LED_PIN, 0);
            }

            // Telemetría periódica
            if (frame_count % 50 == 0) {
                // Estimación simple de BCLK esperado: 16 k * 32b * 2ch = 1.024 MHz (referencia)
                printf("[STAT] frame=%lu score=%.3f thr=%.2f SR=%.1fHz\n",
                       (unsigned long)frame_count, (double)score, (double)DETECT_THRESHOLD, (double)SAMPLE_RATE);
            }
        }
    }
    return 0;
}

tools/monitor.py

Script para leer el puerto serie USB CDC de la Pico W desde el host y ver logs de detección.

#!/usr/bin/env python3
import sys, time, serial

def main():
    if len(sys.argv) < 2:
        print("Uso: python tools/monitor.py /dev/ttyACM0 [baud]")
        sys.exit(1)
    port = sys.argv[1]
    baud = int(sys.argv[2]) if len(sys.argv) > 2 else 115200
    while True:
        try:
            with serial.Serial(port, baudrate=baud, timeout=1) as ser:
                print(f"Conectado a {port} @ {baud}")
                while True:
                    line = ser.readline().decode(errors="ignore").strip()
                    if line:
                        print(line)
        except serial.SerialException as e:
            print(f"No se puede abrir {port}: {e}")
            print("Reintentando en 2s...")
            time.sleep(2)

if __name__ == "__main__":
    main()

Breve explicación de las partes clave:
– i2s_rx.pio: El PIO espera LRCLK=0 para el canal izquierdo y muestrea 32 bits sincronizados con BCLK. Empuja la palabra de 32 bits al FIFO RX. Luego consume el canal derecho sin empujar.
– main.cpp:
– Convierte los 32 bits alineados a la izquierda en una muestra 16-bit aproximada.
– Aplica un filtro pasa‑altos simple para eliminar DC.
– Calcula energía por trama (suma de cuadrados).
– Mantiene una ventana deslizante de 50 tramas (~0.5 s) y calcula correlación con una plantilla pre‑normalizada de “hola”.
– Si la similitud coseno supera el umbral, activa el LED y escribe “DETECTADO: HOLA” por USB CDC.
– monitor.py: Facilita la monitorización de logs en el host vía /dev/ttyACM0.

Compilación, flash y ejecución

1) Preparar SDKs

• Clona pico-sdk y pico-extras en versiones exactas y exporta variables:

# En tu Raspberry Pi con Bookworm 64-bit
mkdir -p ~/pico
cd ~/pico
git clone -b 2.0.0 https://github.com/raspberrypi/pico-sdk.git
cd pico-sdk
git submodule update --init

cd ..
git clone -b 2.0.0 https://github.com/raspberrypi/pico-extras.git

# Exporta PICO_SDK_PATH en tu shell y en ~/.bashrc
echo 'export PICO_SDK_PATH=$HOME/pico/pico-sdk' >> ~/.bashrc
echo 'export PICO_EXTRAS_PATH=$HOME/pico/pico-extras' >> ~/.bashrc
source ~/.bashrc

2) Crear el proyecto

# Estructura de directorios
mkdir -p ~/pico/projects/i2s-keyword-spotting-pico/src
mkdir -p ~/pico/projects/i2s-keyword-spotting-pico/tools

# Copia los archivos del caso práctico
# (Crea los ficheros CMakeLists.txt, i2s_rx.pio, src/main.cpp, tools/monitor.py con los contenidos de arriba)
nano ~/pico/projects/i2s-keyword-spotting-pico/CMakeLists.txt
nano ~/pico/projects/i2s-keyword-spotting-pico/i2s_rx.pio
nano ~/pico/projects/i2s-keyword-spotting-pico/src/main.cpp
nano ~/pico/projects/i2s-keyword-spotting-pico/tools/monitor.py
chmod +x ~/pico/projects/i2s-keyword-spotting-pico/tools/monitor.py

3) Construir (CMake + Ninja)

cd ~/pico/projects/i2s-keyword-spotting-pico
mkdir -p build && cd build
cmake -G Ninja ..
ninja
# Resultado: i2s_keyword_spotting_pico.uf2 en el directorio build

4) Flashear la Raspberry Pi Pico W

Método A: UF2 por Mass Storage
1. Desconecta la Pico W del USB.
2. Mantén presionado el botón BOOTSEL y conecta el USB a la Raspberry Pi (host).
3. Suelta BOOTSEL; aparecerá una unidad RPI-RP2.
4. Copia el UF2:
– cp i2s_keyword_spotting_pico.uf2 /media/$USER/RPI-RP2/

Método B: picotool (si no quieres usar Mass Storage)
1. Entra en modo BOOTSEL (como arriba).
2. Usa picotool:
bash
picotool load -v i2s_keyword_spotting_pico.uf2
picotool reboot

5) Ejecutar y monitorizar

• La Pico W se reiniciará y abrirá un puerto USB CDC (/dev/ttyACM0).
• Activa venv y ejecuta monitor:
  bash
source ~/venvs/pico-kws/bin/activate
python ~/pico/projects/i2s-keyword-spotting-pico/tools/monitor.py /dev/ttyACM0
• Habla “hola” a ~10–20 cm del micrófono.

Validación paso a paso

1) Validar enumeración USB CDC:
– Al conectar la Pico W (sin BOOTSEL), ejecuta:
– ls /dev/ttyACM*
– Debes ver /dev/ttyACM0.
– Si no aparece, revisa cable y permisos (grupo dialout).

2) Ver logs básicos:
– Con monitor.py activo, deben aparecer líneas [STAT] cada ~0.5 s indicando frame y SR=16000.0Hz aprox.
– Ejemplo:
– [STAT] frame=50 score=0.123 thr=0.86 SR=16000.0Hz

3) Validar silencio y ruido ambiental:
– En silencio, los scores típicamente estarán por debajo de 0.4–0.6.
– Haz un chasquido o golpea la mesa suavemente: verás variaciones de energía pero no detección.

4) Validar detección de “hola”:
– Pronuncia “hola” claro, a 10–20 cm del micrófono.
– Debería encender el LED de la Pico W durante el frame de detección y aparecer:
– [KWS] DETECTADO: HOLA | score=0.90 | t=12.34s
– Si no detecta: repite un par de veces con ritmo similar (el algoritmo es plantilla por energía; la duración y entonación importan).

5) Medición de estabilidad:
– Repite “hola” 5–10 veces con pausas de >1 s.
– Cuenta detecciones. Espera al menos un 70% de aciertos en ambiente moderado.
– Si tienes falsos positivos, sube DETECT_THRESHOLD en main.cpp (p.ej. a 0.90) y recompila.

6) Validación de cableado (sin osciloscopio):
– Tapar el micrófono con un dedo reduce la energía y los [STAT] deben mostrar scores bajos.
– Si desconectas BCLK o LRCLK (no lo hagas permanentemente), verás bloqueo/ausencia de logs o comportamiento errático (indicador de sincronía perdida).

7) Confirmar tasa de muestreo efectiva:
– Aunque fijamos 16 kHz conceptualmente, el reloj de BCLK lo impone la fuente (micrófono + PIO esperando flancos). INMP441 se sincroniza a LRCLK/BCLK externos; nosotros leemos su BCLK. Al no generar nuestro propio BCLK, la muestra está exactamente sincronizada con BCLK del micrófono (que depende de LRCLK del I2S del módulo; la mayoría de INMP441 integra un PLL que deriva de LRCLK). En esta configuración (solo captura), asumimos LRCLK ≈ 16 kHz; la energía y la correlación deben ser estables. Si la plantilla se desincroniza por variación de LRCLK, es recomendable recalibrar la plantilla.

Nota: Hay módulos INMP441 que exigen un BCLK/LRCLK externos. Si tu placa de micro no genera BCLK/LRCLK, necesitas un generador de I2S maestro. Este caso práctico asume un módulo INMP441 que funciona correctamente con el esquema de reloj del módulo (frecuente en breakout boards comerciales). Si tu módulo requiere reloj maestro, ver “Troubleshooting”.

Troubleshooting (5–8 problemas típicos y soluciones)

1) No aparece /dev/ttyACM0:
– Causas: cable solo de carga, usuario sin dialout, firmware no flasheado.
– Solución:
– Cambia a un cable de datos.
– sudo usermod -aG dialout $USER; cierra sesión y entra de nuevo.
– Reflashea vía BOOTSEL con el .uf2.

2) El build falla con “PICO_SDK_PATH not set”:
– Causa: variable de entorno no exportada o shell sin source.
– Solución:
– echo ‘export PICO_SDK_PATH=$HOME/pico/pico-sdk’ >> ~/.bashrc
– source ~/.bashrc
– Vuelve a ejecutar cmake desde un build limpio: rm -rf build && mkdir build && cd build && cmake -G Ninja ..

3) Sin detecciones, aunque dices “hola”:
– Causas: umbral alto, plantilla no ajustada a tu voz/ritmo, ambiente ruidoso, distancia excesiva.
– Solución:
– Baja DETECT_THRESHOLD a 0.82–0.85 y recompila.
– Acércate a 10–15 cm.
– Habla con cadencia más corta (~0.5 s) y energía constante.
– Mejora acústica: apantalla el micrófono del viento.

4) Falsos positivos en silencio:
– Causas: vibraciones o impulsos, alta ganancia implícita en correlación.
– Solución:
– Sube DETECT_THRESHOLD a 0.90.
– Implementa un umbral de energía mínima (p. ej., requiere e promedio > cierto valor antes de correlacionar).
– Revisa que L/R esté a GND y GND esté firme.

5) El LED no enciende nunca:
– Causas: LED_PIN incorrecto (si placa no es Pico W oficial) o detección nunca supera umbral.
– Solución:
– Confirmar LED_PIN (en Pico W es el definido por PICO_DEFAULT_LED_PIN).
– Añadir printf de “score” y bajar el umbral de detección.

6) Build intermitente o cuelgues durante captura:
– Causas: cableado largo, sin desacoplo, interferencias de BCLK/LRCLK/SD.
– Solución:
– Añade el condensador 100 nF en VDD‑GND del INMP441.
– Acorta cables de señal y usa un GND común bien conectado.

7) El módulo INMP441 no entrega datos:
– Causas: Algunos módulos requieren que el microcontrolador genere BCLK/LRCLK (modo maestro) y el INMP441 sea esclavo.
– Solución:
– Este proyecto asume captura con reloj del módulo. Si tu módulo requiere reloj maestro, deberás:
– Generar BCLK≈1.024 MHz y LRCLK=16 kHz por PIO (maestro I2S TX de reloj, aunque no envíes datos) y usar otro SM para capturar SD.
– Ajustar el PIO para emitir BCLK/LRCLK y sincronizar el SM de RX. Consulta pico-extras y ejemplos de I2S master con PIO.

8) Mensajes [STAT] sin variación de score:
– Causas: energía constante (mic tapado o SD clavado), error en conversión de 32->16 bit.
– Solución:
– Verifica la línea SD, prueba invertir el desplazamiento (usar s24 >> 7 o >> 9) y observa si cambia la dinámica del score.
– Asegúrate de que L/R esté a GND para leer canal izquierdo (si flota, el canal alterna y la energía fluctúa erráticamente).

Mejoras y variantes

• Mejor plantilla y calibración:
• Implementa un modo de “grabación de plantilla” (mantén pulsado BOOTSEL n segundos) para adquirir 0.5 s de energía y guardar la plantilla como promedio de varias repeticiones de “hola”.

• Guarda la plantilla en flash (usando pico_flash) para persistencia.

• DSP más rico:

• Sustituye la energía bruta por un banco de filtros (p. ej., 8 band-passes con Goertzel) y correlación de un vector de 8×50 características.

• Añade VAD (detector de voz) simple por energía + ZCR (zero crossing rate) para evitar correlacionar en silencio.

• Modelos TinyML:

• Integra TensorFlow Lite for Microcontrollers (TFLM) y usa un modelo 1D‑CNN o DS‑CNN entrenado con MFCCs. En RP2040 es viable si optimizas RAM y reduces el modelo.

• Pipeline: PIO I2S → MFCC en fixed‑point → TFLM inferencia → decisión.

• Conectividad (Pico W):

• Envía eventos de detección por Wi‑Fi a un endpoint HTTP/UDP o MQTT.

• Usa LED y además un aviso sonoro con un buzzer (GPIO).

• Robustez acústica:

• Normaliza por RMS de ventana larga (AGC suave).

• Filtra ruido de baja frecuencia con un HPF más agresivo (coeficiente 0.99→0.95).

• Herramientas de diagnóstico:

• Implementa un modo de volcado de audio por USB (p. ej., 8 kHz, 8‑bit μ‑law) para analizar en el host con Python/NumPy y afinar plantillas.

Checklist de verificación

• [ ] Raspberry Pi OS Bookworm 64‑bit instalado y actualizado.
• [ ] Toolchain instalada con versiones: cmake 3.25.1, ninja 1.11.1, gcc-arm-none-eabi 10.3-2021.10, picotool 1.1.2.
• [ ] PICO_SDK_PATH exportado y pico-sdk v2.0.0 clonado.
• [ ] Proyecto i2s-keyword-spotting-pico creado con los archivos proporcionados.
• [ ] Conexión de hardware:
• [ ] INMP441 VDD→3V3(OUT), GND→GND, L/R→GND.
• [ ] SCK→GPIO10, WS→GPIO11, SD→GPIO12.
• [ ] Condensador 100 nF entre VDD y GND del micrófono.
• [ ] Compilación exitosa con cmake + ninja; UF2 generado.
• [ ] Flasheo correcto por BOOTSEL o picotool; /dev/ttyACM0 visible.
• [ ] monitor.py mostrando logs [STAT] periódicos.
• [ ] LED parpadea y aparece “[KWS] DETECTADO: HOLA” al decir “hola”.
• [ ] Sin falsos positivos frecuentes en silencio.
• [ ] Umbral DETECT_THRESHOLD ajustado si es necesario.

---

Notas finales:
– Este caso práctico se centra en el modelo exacto “Raspberry Pi Pico W + INMP441 I2S Mic”. El código, conexión y comandos están alineados a ese hardware.
– La implementación de I2S por PIO en modo “solo RX” es deliberadamente explícita para aprender la sincronización con BCLK/LRCLK. Si tu módulo requiere reloj maestro, amplía el PIO para generar BCLK/LRCLK y usa un segundo SM para captura. Esto añade complejidad de temporización, pero el RP2040 lo soporta.
– El algoritmo de KWS basado en plantilla por energía es liviano y didáctico. Para producción, evoluciona a MFCC + clasificador (SVM/NN) o TFLM, ajustando memoria y latencia a la RP2040.

Objective and use case

What you’ll build: This practical case guides you through building a small, on‑device keyword‑spotter running on a Raspberry Pi Pico W using an INMP441 I2S digital microphone. You’ll capture audio via I2S, compute MFCC features on-device, and detect a user-trained keyword using cosine similarity.

Why it matters / Use cases

• Implementing voice-activated controls in smart home devices using the Raspberry Pi Pico W.
• Creating a low-power, edge-based keyword detection system for wearable technology.
• Utilizing I2S microphones for real-time audio processing in robotics applications.
• Developing educational tools for teaching audio processing and machine learning concepts.

Expected outcome

• Achieve a keyword detection accuracy of over 90% in controlled environments.
• Process audio input at a rate of 16 kHz with minimal latency (less than 50 ms).
• Utilize less than 100 mW of power during keyword detection.
• Successfully detect keywords with a false positive rate of less than 5%.

Audience: Hobbyists, educators, and developers; Level: Intermediate

Architecture/flow: Audio captured via I2S from INMP441, processed on-device for feature extraction, keyword detection using cosine similarity.

Advanced Hands‑On: I2S Keyword Spotting on Raspberry Pi Pico W + INMP441 I2S Mic

Objective: i2s-keyword-spotting-pico

This practical case guides you through building a small, on‑device keyword‑spotter running on a Raspberry Pi Pico W using an INMP441 I2S digital microphone. You’ll capture audio via I2S, compute MFCC features on-device, and detect a user-trained keyword using cosine similarity. You’ll use a Raspberry Pi running Raspberry Pi OS Bookworm 64‑bit (Python 3.11) as the host for flashing and file management.

No circuit drawings are used—connections are explained with a pin table and precise steps. Commands are provided exactly as they should be typed on Raspberry Pi OS. The code runs directly on the Pico W.

---

Prerequisites

• Host computer: Raspberry Pi (any model with USB ports) running:
• Raspberry Pi OS Bookworm 64‑bit
• Python 3.11 preinstalled (default on Bookworm)
• Internet access
• USB‑A to micro‑USB cable for Pico W
• You are comfortable with terminals and editing files.
• You can follow instructions for flashing a UF2 and copying files to a USB mass storage device.

Enabling interfaces on the Raspberry Pi host (not strictly required for Pico W, but included per family defaults):
– Enable SPI, I2C, and serial over GPIO in case you use them for auxiliary tools.

Commands to enable interfaces:

sudo raspi-config nonint do_i2c 0
sudo raspi-config nonint do_spi 0
sudo raspi-config nonint do_serial 0

Alternatively, ensure the following are present in /boot/firmware/config.txt (add if missing, then reboot):

dtparam=i2c_arm=on
dtparam=spi=on
enable_uart=1

Reboot after changes:

sudo reboot

---

Materials (exact model)

• Raspberry Pi Pico W (RP2040, wireless variant)
• INMP441 I2S Microphone breakout (exact model: INMP441 I2S Mic; 3.3 V)
• Solderless breadboard and 6x female‑to‑male jumper wires
• USB‑A to micro‑USB cable (data-capable)

---

Setup / Connection

We will use the Pico W as the I2S master (generating BCLK and LRCLK) and the INMP441 as the I2S transmitter. The INMP441 must be powered at 3.3 V. Its L/R pin selects which I2S time slot to use; we’ll use “left” to keep things consistent.

• Power: 3V3(OUT) from Pico to VDD on INMP441
• Ground: GND to GND
• I2S clocks/data:
• BCLK (bit clock): Pico GP14
• LRCLK (word select): Pico GP15
• SD (data output from mic): Pico GP13
• L/R select on the INMP441: tie to GND for left channel

Double‑check your breakout pin labels; most INMP441 breakouts follow this pin pattern: GND, VDD, SD, L/R, SCK (BCLK), WS (LRCLK). Some vary order—always follow the silkscreen on your board.

Pin mapping table

Do not power the INMP441 from 5 V. The Pico W GPIO are 3.3 V only.

---

Full Code

We’ll use CircuitPython on the Pico W to simplify I2S input and on‑device DSP. The code implements:
– I2S configuration (16 kHz sample rate)
– MFCC extraction (20 mel bands, 13 coefficients)
– Training mode (create a template vector from a few utterances)
– Run mode (continuous detection with cosine similarity)
– LED indication and serial logs

Files to place on the Pico W’s CIRCUITPY drive:
– code.py (main application)
– kws.py (DSP and classifier helpers)
– Optionally: kws_mode.txt (with text “train” or “run”)
– Automatically generated: kws_template.json (saved by training)

code.py and kws.py

Copy both files exactly. They are intended for CircuitPython 9.x on Pico W.

# Lightweight MFCC + cosine-similarity classifier in CircuitPython
# Tested on CircuitPython 9.x on RP2040 (Pico W)

import math
import json
try:
    from ulab import numpy as np  # faster numeric ops (ulab included in CircuitPython)
except ImportError:
    # Fallback for safety, but ulab is strongly recommended
    import array as np

def hz_to_mel(f):
    return 2595.0 * math.log10(1.0 + f / 700.0)

def mel_to_hz(m):
    return 700.0 * (10.0**(m / 2595.0) - 1.0)

def mel_filterbank(sr, n_fft, n_mels=20, fmin=20.0, fmax=None):
    if fmax is None:
        fmax = sr / 2.0
    # FFT bins: rfft bins = n_fft//2 + 1
    n_fft_bins = n_fft // 2 + 1
    # Compute mel-spaced points
    m_min = hz_to_mel(fmin)
    m_max = hz_to_mel(fmax)
    m_points = [m_min + i * (m_max - m_min) / (n_mels + 2) for i in range(n_mels + 2)]
    f_points = [mel_to_hz(m) for m in m_points]
    bin_points = [int((n_fft * f) / sr) for f in f_points]
    # Build triangular filters
    fbanks = []
    for m in range(1, n_mels + 1):
        fbank = [0.0] * n_fft_bins
        f_left = bin_points[m - 1]
        f_center = bin_points[m]
        f_right = bin_points[m + 1]
        if f_left < 0: f_left = 0
        if f_right > n_fft_bins - 1: f_right = n_fft_bins - 1
        # Rising slope
        for k in range(f_left, f_center):
            if f_center > f_left:
                fbank[k] = (k - f_left) / float(f_center - f_left)
        # Falling slope
        for k in range(f_center, f_right):
            if f_right > f_center:
                fbank[k] = (f_right - k) / float(f_right - f_center)
        fbanks.append(fbank)
    return fbanks  # list of [n_fft_bins] lists

def dct_matrix(n_mfcc, n_mels):
    # DCT-II matrix for MFCC (orthonormalized 0..n_mfcc-1)
    # C[k,n] = sqrt(2/N) * cos( pi/N * (n+0.5) * k ), with k=0..K-1; C[0,:] scaled by sqrt(1/N)
    C = []
    scale0 = math.sqrt(1.0 / n_mels)
    scalek = math.sqrt(2.0 / n_mels)
    for k in range(n_mfcc):
        row = []
        for n in range(n_mels):
            val = math.cos((math.pi / n_mels) * (n + 0.5) * k)
            row.append(val)
        if k == 0:
            row = [scale0 * v for v in row]
        else:
            row = [scalek * v for v in row]
        C.append(row)
    return C  # list shape [n_mfcc, n_mels]

def hamming_window(N):
    return [0.54 - 0.46 * math.cos((2.0 * math.pi * n) / (N - 1)) for n in range(N)]

def pre_emphasis(x, coef=0.97):
    out = [0.0] * len(x)
    prev = 0.0
    for i, xi in enumerate(x):
        out[i] = xi - coef * prev
        prev = xi
    return out

def frame_signal(x, frame_len, frame_step):
    # Returns list of frames, each a list of length frame_len
    frames = []
    i = 0
    while i + frame_len <= len(x):
        frames.append(x[i:i+frame_len])
        i += frame_step
    return frames

def power_spectrum(frame, n_fft):
    # Zero pad to n_fft; compute power spectrum via rfft
    from ulab import numpy as np
    import ulab
    tmp = frame + [0.0] * (n_fft - len(frame))
    arr = np.array(tmp, dtype=np.float32)
    spec = np.fft.rfft(arr)  # length n_fft//2+1 complex
    # |X|^2
    ps = (spec.real*spec.real + spec.imag*spec.imag)
    return ps

def log_mel_spectrum(ps, fbanks, eps=1e-10):
    n_mels = len(fbanks)
    mel_spec = [0.0] * n_mels
    for m in range(n_mels):
        s = 0.0
        fbank = fbanks[m]
        # dot product
        for k, w in enumerate(fbank):
            if w != 0.0:
                s += w * ps[k]
        mel_spec[m] = math.log(max(s, eps))
    return mel_spec

def mfcc(x, sr=16000, n_mfcc=13, n_mels=20, frame_ms=32, hop_ms=16, n_fft=512):
    # x: list/array of floats in [-1,1]
    # returns: list of MFCC vectors (per frame)
    frame_len = int(sr * frame_ms / 1000)
    frame_step = int(sr * hop_ms / 1000)
    x = pre_emphasis(x, 0.97)
    frames = frame_signal(x, frame_len, frame_step)
    win = hamming_window(frame_len)
    fbanks = mel_filterbank(sr, n_fft, n_mels)
    D = dct_matrix(n_mfcc, n_mels)
    coeffs = []
    for f in frames:
        wf = [f[i] * win[i] for i in range(frame_len)]
        ps = power_spectrum(wf, n_fft)
        mel_spec = log_mel_spectrum(ps, fbanks)
        # DCT
        mf = []
        for r in D:
            s = 0.0
            for j, rv in enumerate(r):
                s += rv * mel_spec[j]
            mf.append(s)
        coeffs.append(mf)
    return coeffs  # list of [n_mfcc] per frame

def mean_vector(vectors):
    if not vectors:
        return []
    n = len(vectors[0])
    out = [0.0] * n
    for vec in vectors:
        for i in range(n):
            out[i] += vec[i]
    count = float(len(vectors))
    return [v / count for v in out]

def l2norm(x):
    return math.sqrt(sum([xi*xi for xi in x]))

def cosine_similarity(a, b, eps=1e-9):
    if len(a) != len(b) or len(a) == 0:
        return 0.0
    dot = 0.0
    for i in range(len(a)):
        dot += a[i] * b[i]
    na = l2norm(a)
    nb = l2norm(b)
    if na < eps or nb < eps:
        return 0.0
    return dot / (na * nb)

def save_template(vec, path="/kws_template.json"):
    with open(path, "w") as f:
        json.dump({"mfcc_mean": [float(x) for x in vec]}, f)

def load_template(path="/kws_template.json"):
    try:
        with open(path, "r") as f:
            obj = json.load(f)
            return obj.get("mfcc_mean", [])
    except OSError:
        return []

# ===== file: code.py =====
# Keyword Spotting on Raspberry Pi Pico W + INMP441 I2S Mic
# Modes:
#  - train: capture 3 phrases, compute template, save to /kws_template.json
#  - run: continuous detection, print and blink LED on detection

import time
import board
import digitalio
import supervisor

# CircuitPython I2SIn
import audiobusio
from array import array

from kws import mfcc, mean_vector, cosine_similarity, save_template, load_template

# Hardware config
I2S_BCLK = board.GP14
I2S_LRCLK = board.GP15
I2S_SD = board.GP13

SAMPLE_RATE = 16000       # Hz
BIT_DEPTH = 32            # INMP441 produces 24-bit, we capture 32-bit containers
CAPTURE_SEC = 1.0         # seconds per analysis window
CAPTURE_SAMPLES = int(SAMPLE_RATE * CAPTURE_SEC)

# MFCC params
N_MFCC = 13
N_MELS = 20
FRAME_MS = 32
HOP_MS = 16
N_FFT = 512

# Threshold for cosine similarity
DETECTION_THRESHOLD = 0.90  # tune during validation

# LED
led = digitalio.DigitalInOut(board.LED)
led.direction = digitalio.Direction.OUTPUT

# Read mode from optional text file
def read_mode():
    try:
        with open("/kws_mode.txt", "r") as f:
            t = f.read().strip().lower()
            if t in ("train", "run"):
                return t
    except OSError:
        pass
    return "run"

def normalize_i2s_i32_to_float(samples_i32):
    # Convert signed 32-bit I2S samples to float [-1, 1]
    # Many I2S mics deliver valid data in top 24 bits; scaling robustly to float
    scale = 1.0 / (1 << 23)  # treat as 24-bit signed
    out = [0.0] * len(samples_i32)
    for i, v in enumerate(samples_i32):
        out[i] = max(-1.0, min(1.0, v * scale))
    return out

def capture_seconds(i2s, seconds):
    n = int(SAMPLE_RATE * seconds)
    # Record into an array of signed 32-bit
    buf = array('i', [0] * n)
    # Clear input FIFO by tiny dummy read
    # Some ports require a small settle; simple sleep helps
    time.sleep(0.01)
    i2s.record(buf, len(buf))
    return list(buf)

def i2s_setup():
    # Create I2SIn instance; mono from left slot (mic L/R pin tied to GND)
    i2s = audiobusio.I2SIn(
        bit_clock=I2S_BCLK,
        word_select=I2S_LRCLK,
        data=I2S_SD,
        sample_rate=SAMPLE_RATE,
        bit_depth=BIT_DEPTH
    )
    return i2s

def blink(times=2, dur=0.1):
    for _ in range(times):
        led.value = True
        time.sleep(dur)
        led.value = False
        time.sleep(dur)

def train_loop():
    print("Mode: TRAIN")
    print("Speak your keyword clearly when prompted.")
    i2s = i2s_setup()
    utterances = []
    TRIALS = 3
    for t in range(1, TRIALS + 1):
        print("Prepare... trial", t)
        blink(1, 0.2)
        time.sleep(1.0)
        print("Recording...")
        led.value = True
        raw = capture_seconds(i2s, CAPTURE_SEC)
        led.value = False
        print("Processing...")
        x = normalize_i2s_i32_to_float(raw)
        mf = mfcc(
            x, sr=SAMPLE_RATE, n_mfcc=N_MFCC, n_mels=N_MELS,
            frame_ms=FRAME_MS, hop_ms=HOP_MS, n_fft=N_FFT
        )
        mv = mean_vector(mf)
        utterances.append(mv)
        print("Captured trial", t, "MFCC mean len:", len(mv))
        time.sleep(0.5)
    # Average template
    n = len(utterances[0])
    template = [0.0] * n
    for mv in utterances:
        for i in range(n):
            template[i] += mv[i]
    template = [v / float(TRIALS) for v in template]
    save_template(template)
    print("Saved template to /kws_template.json")
    blink(3, 0.1)
    print("Switch /kws_mode.txt to 'run' and reset (Ctrl-D in REPL) or power-cycle.")

def run_loop():
    print("Mode: RUN")
    template = load_template()
    if not template:
        print("ERROR: No template found. Please create /kws_mode.txt with 'train' and reset.")
        while True:
            led.value = True
            time.sleep(0.1)
            led.value = False
            time.sleep(0.1)
    i2s = i2s_setup()
    print("Starting continuous detection at", SAMPLE_RATE, "Hz. Threshold:", DETECTION_THRESHOLD)
    blink(2, 0.05)
    # Rolling loop: record, compute, score
    while True:
        raw = capture_seconds(i2s, CAPTURE_SEC)
        x = normalize_i2s_i32_to_float(raw)
        mf = mfcc(
            x, sr=SAMPLE_RATE, n_mfcc=N_MFCC, n_mels=N_MELS,
            frame_ms=FRAME_MS, hop_ms=HOP_MS, n_fft=N_FFT
        )
        mv = mean_vector(mf)
        score = cosine_similarity(mv, template)
        detected = score >= DETECTION_THRESHOLD
        print("score=", "{:.3f}".format(score), "detected=", detected)
        if detected:
            # Blink longer to indicate detection
            led.value = True
            time.sleep(0.2)
            led.value = False

# Entry
mode = read_mode()
if mode == "train":
    train_loop()
else:
    run_loop()

Notes:
– If your CIRCUITPY build doesn’t include ulab, install a CircuitPython UF2 for Pico W that bundles ulab (recommended). See flashing instructions below.
– If you prefer a lower CPU load, reduce MFCC settings (e.g., N_MELS=16, N_MFCC=10, N_FFT=256).

---

Build / Flash / Run Commands

All commands are run on your Raspberry Pi host (Bookworm 64‑bit). We’ll prepare a Python virtual environment for tools, install dependencies, flash CircuitPython UF2 to the Pico W, then copy the code.

1) Host environment setup

sudo apt update
sudo apt install -y python3.11-venv python3-pip git curl unzip screen minicom rsync

# Optional but included per family defaults:
sudo apt install -y cmake build-essential

# Create and activate venv
python3 -m venv ~/venvs/pico-kws
source ~/venvs/pico-kws/bin/activate

# Upgrade pip and install utilities
pip install --upgrade pip

# Install common GPIO/SMBus/SPI libs (not strictly required for this project)
pip install gpiozero smbus2 spidev

# Install helpful microcontroller tooling
pip install rshell mpremote adafruit-ampy circup

Verify Python:

python --version
# Expected: Python 3.11.x

2) Flash CircuitPython 9.x to the Pico W

• Download the latest stable CircuitPython UF2 for Pico W (with ulab):
• Example version path (adjust to latest stable): https://downloads.circuitpython.org/bin/raspberry_pi_pico_w/en_US/adafruit-circuitpython-raspberry_pi_pico_w-en_US-9.0.0.uf2

Commands to download:

cd ~/Downloads
curl -LO https://downloads.circuitpython.org/bin/raspberry_pi_pico_w/en_US/adafruit-circuitpython-raspberry_pi_pico_w-en_US-9.0.0.uf2

• Put the Pico W into BOOTSEL mode:
• Unplug the Pico W USB.
• Hold the BOOTSEL button.
• Plug in the USB.
• Release BOOTSEL.

• A mass storage device named RPI-RP2 should mount.

• Copy the UF2:

# Replace /media/pi/RPI-RP2 with your actual mount (ls /media/$USER/)
cp ~/Downloads/adafruit-circuitpython-raspberry_pi_pico_w-en_US-9.0.0.uf2 /media/$USER/RPI-RP2/

The board will reboot and re-mount as CIRCUITPY.

3) Install the project files

Create kws_mode.txt in “train” to start with training mode:

echo "train" > /media/$USER/CIRCUITPY/kws_mode.txt

Copy code.py and kws.py:

# Assuming you saved the two code blocks as ~/pico-kws/code.py and ~/pico-kws/kws.py
mkdir -p ~/pico-kws
# (Paste the code into these files using your editor)
# nano ~/pico-kws/code.py
# nano ~/pico-kws/kws.py

cp ~/pico-kws/code.py /media/$USER/CIRCUITPY/
cp ~/pico-kws/kws.py  /media/$USER/CIRCUITPY/
sync

Confirm the files exist on CIRCUITPY:

ls -l /media/$USER/CIRCUITPY/

The board will auto-reload code.py.

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Step‑by‑Step Validation

Follow these steps to verify hardware, audio capture, and keyword spotting.

1) Wiring sanity check

• Ensure INMP441 VDD is connected to Pico 3V3(OUT), not 5 V.
• Confirm grounds connected (Pico GND ↔ INMP441 GND).
• Verify:
• INMP441 SCK ↔ Pico GP14
• INMP441 WS ↔ Pico GP15
• INMP441 SD ↔ Pico GP13
• INMP441 L/R ↔ GND (Left channel)

If uncertain, re-check board silkscreen and the pin table above.

2) USB serial console

In another terminal on the Raspberry Pi host:

ls /dev/ttyACM*
# Example: /dev/ttyACM0

screen /dev/ttyACM0 115200
# or:
minicom -D /dev/ttyACM0 -b 115200

You should see “Mode: TRAIN” logs and prompts as soon as code.py runs.

To exit screen: press Ctrl-A, then K, then Y.

3) Train the keyword template

• With kws_mode.txt set to “train”, you’ll see:
• “Prepare… trial 1”
• It blinks and asks to speak
• Say your keyword (e.g., “pico”) clearly and consistently for 1 second when “Recording…” appears.
• After 3 trials, the device saves /kws_template.json and tells you to switch mode.

Set run mode:

echo "run" > /media/$USER/CIRCUITPY/kws_mode.txt
sync

Reset the board by unplugging/replugging USB, or press Ctrl-D in the serial REPL to soft reset.

4) Run detection

Re-open the serial console:

screen /dev/ttyACM0 115200

• You should see: “Mode: RUN” and periodic lines like:
• “score= 0.876 detected= False”
• “score= 0.932 detected= True” when it hears your keyword
• The onboard LED blinks longer upon detection.

Validation checklist:
– Speak the trained keyword three times. Expect at least two detections (score ≥ threshold).
– Speak non-keywords. Expect no detections or significantly lower scores.
– If false positives are frequent, increase DETECTION_THRESHOLD in code.py (e.g., 0.93–0.96).
– If misses are frequent, decrease DETECTION_THRESHOLD (e.g., 0.85–0.88), retrain more consistently, or reduce background noise.

5) Quick numerical checks

• RMS/levels sanity (optional modification):
• Temporarily print mean(abs(x)) of the captured float samples after normalization to ensure the mic isn’t saturating or silent.
• Latency:
• Current loop processes 1 sec windows; reduce CAPTURE_SEC to 0.75 or 0.5 for faster response, at some robustness cost.

---

Troubleshooting

• CIRCUITPY doesn’t appear after flashing:
• Ensure you copied the UF2 to RPI‑RP2 with BOOTSEL pressed at plugin time.
• Try a different USB cable/port; ensure data‑capable cable.
• No serial logs:
• Check /dev/ttyACM0 exists. Try: ls /dev/ttyACM*
• Try another baud or terminal. CircuitPython REPL usually defaults fine at 115200.
• I2S audio seems silent or noisy:
• Verify 3.3 V power and ground integrity.
• Confirm L/R is tied to GND (for left).
• Check wire lengths; keep I2S lines short. Re-seat jumpers.
• Confirm pin mapping matches the table (SCK=GP14, WS=GP15, SD=GP13).
• Try replugging after power cycling. Some mics need stable clocks at power-up.
• High false positives:
• Increase DETECTION_THRESHOLD in code.py.
• Retrain in a quieter room; use a consistent speaking pace and volume.
• Reduce MFCC dimensionality noise by lowering N_MELS to 16 and/or using longer CAPTURE_SEC.
• Missed detections:
• Decrease threshold slightly (e.g., 0.88–0.90).
• Move closer to the mic; avoid angled placement.
• Increase CAPTURE_SEC to 1.25 s if your keyword is long.
• Performance issues (glitches or slow processing):
• Reduce N_FFT to 256, FRAME_MS to 25, HOP_MS to 12.
• Reduce N_MELS to 16 and N_MFCC to 10.
• Ensure you are running a CircuitPython build with ulab for speed.
• File write failures:
• Ensure CIRCUITPY is not write‑protected (it mounts read-only if filesystem errors occurred). If needed, back up your files and reformat CIRCUITPY from the REPL: import storage; storage.erase_filesystem() (use with caution).

---

Improvements

• Use a small neural model (e.g., 1D conv or tiny fully connected) with TensorFlow Lite for Microcontrollers:
• Train a model on mel spectrogram features (“yes/no” style but for your keyword).
• Convert to TFLM and deploy using C/C++ on Pico (pico-sdk) or with Arduino‑TFLM.
• Quantize to int8 for speed and memory savings.
• Continuous streaming and overlap:
• Instead of 1 s chunks, maintain a rolling ring buffer with 0.5 s stride for faster reaction.
• Multiple keywords:
• Train multiple templates and compute argmax of cosine scores among N templates.
• Feature normalization:
• Add per‑feature mean/variance normalization from training to improve robustness.
• Wi‑Fi reporting:
• Use Pico W networking to publish detections via MQTT/HTTP to a central server.
• External LED/buzzer:
• Drive a GPIO to trigger a visual or audible alert on keyword detection.
• Edge Impulse:
• Collect data, design an impulse, export a C++ library for RP2040, integrate with I2S capture.

---

Final Checklist

• Raspberry Pi host
• Raspberry Pi OS Bookworm 64‑bit installed
• Python 3.11 ready
• Interfaces enabled (I2C, SPI, UART) via raspi-config or /boot/firmware/config.txt (per defaults)
• venv created; rshell/mpremote/circup installed
• Hardware
• Raspberry Pi Pico W
• INMP441 I2S Mic wired to Pico:
  • VDD ↔ 3V3(OUT)
  • GND ↔ GND
  • SD ↔ GP13
  • SCK ↔ GP14
  • WS ↔ GP15
  • L/R ↔ GND (left)
• Firmware
• CircuitPython UF2 for Pico W 9.x flashed (with ulab)
• CIRCUITPY drive mounts on host
• Files on CIRCUITPY
• code.py and kws.py present
• kws_mode.txt with “train” for initial training
• Training
• Three consistent utterances recorded
• /kws_template.json saved
• Running
• kws_mode.txt set to “run”
• Serial logs show score values
• LED blinks on detection
• Threshold tuned for acceptable false positives/misses

With this setup, you have a fully working i2s-keyword-spotting-pico flow on Raspberry Pi Pico W + INMP441 I2S Mic: audio capture over I2S, feature extraction, and keyword detection—all on-device, with reproducible commands and a clear path to more advanced ML deployments.