What you'll learn

Common-anode versus common-cathode LEDs
PWM brightness control with PWM
Mixing red, green and blue
Inverting a value with 1023 minus brightness

Difficulty: Beginner
Time: About 15 minutes
Board: ESP32-DevKitC V4
Parts: 6

How it works

This is a common-anode RGB LED. Its shared leg connects to 3.3 V, and each color leg goes through a 220 Ω resistor to a GPIO pin: red on 4, green on 2, blue on 15. A color lights when its pin is LOW, which is the opposite of what you might expect.

The program drives each pin with PWM and flips the numbers: a duty of 1023 minus the brightness. Every 200 ms it picks three random brightness values from 0 to 1023, shows the color, and prints the numbers.

Parts list

6 parts, plus the jumper wires. They retail for about $10.40; on Mokxi they're free.

1 × ESP32-DevKitC V4
1 × RGB LEDIn Starter Projects Kit.
3 × Resistor, 220 ΩIn Starter Kit, Claw Machine Kit, Halloween Prop Kit.
1 × Power, 3.3 V

Kits that can build it

These 3 starter kits have every part in the circuit. Each kit's page lists what else it can build.

Wiring table

Every connection, pin by pin, read from the circuit itself. Each row joins the pin on the left to the pin on the right, by a jumper wire or a breadboard strip.

Part and pin	Connects to
Resistor, 220 Ω (1) pin 1	ESP32-DevKitC V4 pin 4
Resistor, 220 Ω (2) pin 1	ESP32-DevKitC V4 pin 2
Resistor, 220 Ω (3) pin 1	ESP32-DevKitC V4 pin 15
Resistor, 220 Ω (1) pin 2	RGB LED pin R
RGB LED pin C	3.3 V
Resistor, 220 Ω (2) pin 2	RGB LED pin G
Resistor, 220 Ω (3) pin 2	RGB LED pin B

The code

The MicroPython code exactly as the editor opens it. Change a line there and press Run: the board runs it on the official MicroPython firmware, with nothing to compile.

main.py · ESP32-DevKitC V4

# Random color: a common-anode RGB LED on GPIO 4 (red), 2 (green) and
# 15 (blue). A color lights when its pin is LOW, so each duty is
# written as 1023 minus the brightness. A new random color every 200 ms.
from machine import Pin, PWM
import random
import time

red = PWM(Pin(4), freq=10000)
green = PWM(Pin(2), freq=10000)
blue = PWM(Pin(15), freq=10000)

def color(r, g, b):
    red.duty(1023 - r)
    green.duty(1023 - g)
    blue.duty(1023 - b)

while True:
    r, g, b = random.randint(0, 1023), random.randint(0, 1023), random.randint(0, 1023)
    color(r, g, b)
    print("color", r, g, b)
    time.sleep_ms(200)

Code walkthrough

The key functions of the sketch, and what each one does.

`color` main.py

Takes brightness values for red, green and blue, each 0 to 1023. Since the LED lights when a pin is low, each duty is set to 1023 minus the value. So a brightness of 1023 gives a duty of 0, and that color is fully on.

def color(r, g, b):
    red.duty(1023 - r)
    green.duty(1023 - g)
    blue.duty(1023 - b)

Troubleshooting

The usual mistakes with this circuit, and the fix for each.

The colors look backward: bright when they should be dim This project
This LED is common anode. The shared leg goes to 3.3 V, and the code subtracts from 1023.
One color never shows This project
Check that each color leg goes through its own resistor to the right pin: 4, 2 and 15.
The colors are wrong or one color never lights. RGB LED
Check whether your LED is common cathode (shared leg to ground) or common anode (shared leg to 5 V). Common anode works backwards: LOW turns a color on.
One color is much brighter than the others, or the LED runs too hot. RGB LED
Use one resistor per color leg, never one for the shared leg. Typical values are 220 ohm for red and 100 to 150 ohm for green and blue on 5 V.
The LED is dim, burns out, or the pin reads wrong because the resistor value is off. Resistor
Read the color bands again. A 220 ohm to 330 ohm resistor suits a typical LED on 5 V. 10k is a common pull-up or pull-down value. Check with a multimeter if unsure.
A pull-up or pull-down resistor is missing, so the input floats and reads random values. Resistor
Tie the input to 5 V or ground through about 10k. Or use INPUT_PULLUP and wire the switch to ground.
The board is not found, or upload fails with a connecting message. ESP32-DevKitC V4
Use a USB cable that carries data, not charge only. Pick the ESP32 Dev Module board. If it still fails, hold BOOT while uploading starts, then release.
Some pins never read right, or the board will not boot with a wire attached. ESP32-DevKitC V4
GPIO34 to 39 are input only and have no pull-ups. GPIO6 to 11 run the flash, so leave them alone. GPIO0, 2 and 12 are boot pins; avoid pulling them the wrong way at reset.