ElectronicsQUICK REFERENCE
Resistors & LEDs
Read polarity and choose a resistor before lighting your first LED.
01LED polarity
- Anode (+)
- Usually the longer lead on an untrimmed through-hole LED.
- Cathode (−)
- Usually shorter lead / flat case edge; confirm with diode-test mode.
- Series circuit
- GPIO → resistor → LED anode; LED cathode → GND. Resistor may also go on the cathode side.
02Choose resistance
- Formula
- R = (Vsupply − Vforward) / Iled, with current in amperes.
- Example
- 5 V supply, 2 V red LED, 5 mA: R = 600 ohm; choose 680 ohm.
- Power
- Presistor = I² × R. Choose a power rating with margin.
03Bench values
- Common values
- 220, 330, 470, 680 ohm; 1 kohm, 4.7 kohm, 10 kohm. Calculate for your circuit.
- 4-band code
- First two bands = digits, third = multiplier, fourth = tolerance. Brown-black-red-gold = 1 kohm ±5%.
- Digits
- Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9.