Circuits / Microcontrollers
Arduino UNO: an RGB LED mixes colours (PWM)
Three LEDs in one dome, each with its own resistor: their brightness, set by PWM, adds up to the colour the eye sees
Tap a part to see its voltages and currents. It is a model, not a measurement.
What do you need?
- Development board Arduino UNOSearch on Amazon
- Resistor 220 Ω × 3Search on Amazon
- RGB LED RGB, common cathodeSearch on Amazon
- Jumper wires × 6Search on Amazon
- BreadboardSearch on Amazon
How does an Arduino mix colours with an RGB LED?
An RGB LED is three small LEDs in one dome, red, green and blue, sharing one leg: here the common cathode, tied to GND. Each chip has its own pin and resistor: D9, D10 and D11, through 220 Ω each. They need separate resistors because red asks for less voltage, about 1.9 V against 3 V for green and blue. So the same 220 Ω gives red about 12 mA and the other two about 7.6 mA. analogWrite sets each chip's share of the time on, from 0 to 255, switching about 490 times per second. The chips are too close and too fast for your eye to separate, so it adds them: red and green look yellow, green and blue cyan, red and blue magenta, all three white. The program's last colour, 255 red with 40 green, is orange: green is on only about 16 % of the time. To balance the white, change the resistors, since equal resistors do not give equal light.
Values from the Protoboard ISO simulation: a model, not a bench measurement.
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