Practical case: Calculate the value with the color code

Materials

• 1× Resistor R1 (4-band example: Brown–Black–Red–Gold; nominal 1 kΩ ±5%)
• 1× Breadboard
• 1× DC supply (+5 V recommended)
• 1× Digital multimeter (DMM) with V, A, and Ω modes
• 3× Jumper wires (male–male)
• 1× Resistor color code chart (printout or app)

Wiring guide

• Abbreviations used:
• V_R = voltage across resistor R1, measured between the black dots labeled V_R+ and V_R-.

• I_R = current through R1, measured with the DMM in series at the black dots labeled I_R.

• Read the color code on R1 before wiring:

• 1st band = first digit; 2nd band = second digit; 3rd band = multiplier; 4th band = tolerance.

• Example R1: Brown (1), Black (0), Red (×10^2), Gold (±5%) → 10 × 100 = 1000 Ω (1 kΩ) ±5%.

• Power off the supply while building the circuit.

• Place R1 on the breadboard so it connects between two separate rows.
• Connect +V to one end of R1 via a jumper; connect the other end of R1 to GND.
• For V_R measurement (DMM in DC volts):
• Red probe to the black dot labeled V_R+ (top of R1).
• Black probe to the black dot labeled V_R- (bottom of R1, at GND side).
• For I_R measurement (DMM in current mode, mA range):
• Break the jumper between +V and R1’s top node.
• Insert the DMM in series at the two black dots labeled I_R (observe polarity if your meter indicates it).
• For resistance check (Ω mode):
• Power off and disconnect +V.
• Place the probes across the same V_R+ and V_R- dots to read Ω (resistance is measured with no power).

Schematic

                +5 V
                 │
                 ├────────● IR ──● VR+ ──● RΩ+ ───────┐
                 │                                     │
                                                       ┌┴┐   R1 = Resistor 4 bandas (p.ej. marrón‑negro‑rojo‑dorado)
                                                       │ │
                                                       │ │
                                                       └┬┘
                                                        │
                                  ● VR− ──● RΩ− ────────┤
                                                        │
                                                       GND

Measurements and tests

• Calculate by color code:

  • Identify bands on R1: 1st digit, 2nd digit, multiplier, tolerance.
  • Example: Brown=1, Black=0 → “10”; Red multiplier=10^2 → 10 × 100 = 1000 Ω.
  • Tolerance Gold=±5% → acceptable range: 950 Ω to 1050 Ω.

• Verify resistance (power off, Ω mode):

  • Disconnect +V. Place probes across ● V_R+ and ● V_R-.
  • Expected: 1 kΩ within ±5% (950–1050 Ω).
  • If reading is unstable, lift one end of R1 from the breadboard to avoid parallel paths.

• Verify with voltage and current (powered):

  • Set supply to +5.00 V.
  • Measure V_R across ● V_R+ and ● V_R- (expect ~5.00 V in a single-resistor-to-GND circuit).
  • Insert ammeter in series at the two ● I_R points (mA range).
  • Compute expected I_R = V_R / R_measured. For 5.00 V and 1.00 kΩ: I_R ≈ 5.00 mA.
  • Compare measured I_R to expected. Differences beyond tolerance may indicate wiring errors or a mislabeled resistor.

• Optional cross-check:

  • Swap R1 for a different color code (e.g., Red–Violet–Brown–Gold = 270 Ω).
  • Repeat the three steps to reinforce the method.

Common mistakes and tips

• Reading bands in reverse: locate the tolerance band (Gold/Silver) at the far end; start reading from the opposite side.
• Measuring resistance with power applied: always power OFF and discharge nodes before Ω measurements.
• Wrong meter jack/range: use the mA jack/range for small currents; return the lead to V/Ω jack for voltage/resistance.
• Loose breadboard rows: ensure R1 legs are in separate rows; tug gently on jumpers to confirm good contact.
• Color confusion: in poor light, Brown vs. Red or Black vs. Brown can be misread—use a color chart and good lighting.

Safety

• Never measure resistance on a live circuit.
• Avoid shorting +V to GND with the ammeter by mistake; double-check lead placement before powering.
• If using a 9 V battery, note that I_R will be higher (e.g., ~9 mA for 1 kΩ); ensure the meter range is appropriate.

Improvements

• Extend to 5-band/6-band resistors (adds a third digit and temperature coefficient).
• Build a small divider (two resistors) and validate one by solving from measured node voltage.
• Create a quick-reference card with color→digit mapping for your toolkit.

More Practical Cases on Prometeo.blog

Carlos Núñez Zorrilla

Electronics & Computer Engineer

Telecommunications Electronics Engineer and Computer Engineer (official degrees in Spain).

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