Practical case: sump pump alarm with Arduino UNO

/*
 * sump_controller.ino
 * Dual-float sump pump controller with hysteresis and high-water alarm.
 * Target: Arduino UNO R3 (ATmega328P)
 */

// --- Pin Definitions ---
const int LOW_FLOAT_PIN = 2;
const int HIGH_FLOAT_PIN = 3;
const int RELAY_PIN = 4;
const int BUZZER_PIN = 5;

// --- Logic Definitions ---
// Using INPUT_PULLUP: Switch closed (floating up) connects to GND (LOW)
const int FLOAT_TRIGGERED = LOW;
const int FLOAT_RESTING = HIGH;

// Standard 5V relay modules are typically Active LOW
const int RELAY_ON = LOW;
const int RELAY_OFF = HIGH;

// --- Alarm Configuration ---
// Time in milliseconds before triggering alarm if High Float stays triggered
const unsigned long ALARM_DELAY_MS = 5000; 

// --- State Variables ---
bool pumpIsActive = false;
bool alarmIsActive = false;
unsigned long highFloatStartTime = 0;

void setup() {
  Serial.begin(9600);
  while (!Serial) { ; } // Wait for serial port to connect

  Serial.println("Initializing Sump Pump Controller...");

  // Configure float switch pins with internal pull-ups
  pinMode(LOW_FLOAT_PIN, INPUT_PULLUP);
  pinMode(HIGH_FLOAT_PIN, INPUT_PULLUP);

  // Configure output pins
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);

  // Set initial safe states
  digitalWrite(RELAY_PIN, RELAY_OFF);
  noTone(BUZZER_PIN);

  Serial.println("System Ready.");
  Serial.println("-----------------------------------");
}

void loop() {
  // 1. Read the current state of both float switches
  int lowFloatState = digitalRead(LOW_FLOAT_PIN);
  int highFloatState = digitalRead(HIGH_FLOAT_PIN);

  // 2. Evaluate Hysteresis Logic for the Pump
  if (highFloatState == FLOAT_TRIGGERED) {
    // Water has reached the top float. Turn pump ON.
    if (!pumpIsActive) {
      pumpIsActive = true;
      digitalWrite(RELAY_PIN, RELAY_ON);
      Serial.println("ACTION: High level reached. Pump turned ON.");
    }
  } 
  else if (lowFloatState == FLOAT_RESTING) {
    // Water has dropped below the bottom float. Turn pump OFF.
    if (pumpIsActive) {
      pumpIsActive = false;
      digitalWrite(RELAY_PIN, RELAY_OFF);
      Serial.println("ACTION: Low level cleared. Pump turned OFF.");
    }
  }
  // Note: If water is between the two floats, pumpIsActive retains its previous state.
  // This is the core of hysteresis.

  // 3. Evaluate Alarm Logic (Non-blocking timer)
  if (highFloatState == FLOAT_TRIGGERED) {
    // If this is the first moment we see the high float triggered, record the time
    if (highFloatStartTime == 0) {
      highFloatStartTime = millis();
    }

    // Check if the high float has been triggered longer than the allowed delay
    if ((millis() - highFloatStartTime >= ALARM_DELAY_MS) && !alarmIsActive) {
      alarmIsActive = true;
      tone(BUZZER_PIN, 2000); // 2kHz warning tone
      Serial.println("ALARM: Water level critically high! Pump may be failing.");
    }
  } else {
    // Water is no longer at the high float. Reset alarm states.
    if (highFloatStartTime != 0 || alarmIsActive) {
      highFloatStartTime = 0;
      alarmIsActive = false;
      noTone(BUZZER_PIN);
      Serial.println("STATUS: High water condition cleared. Alarm reset.");
    }
  }

  // Small delay to debounce switch chattering from simulated water ripples
  delay(100); 
}