What you'll learn

A color wheel that turns one number into a color
Spreading colors across pixels with an offset
Animating by shifting a start value
Wrapping a counter with the modulo operator

Difficulty: Beginner
Time: About 10 minutes
Board: ESP32-DevKitC V4
Parts: 3

How it works

Eight WS2812 LEDs share one data line on GPIO 2. The program gives each pixel a color from a color wheel, spacing them 32 steps apart, so together they show a rainbow.

Every 10 ms the start point moves along the wheel by 4 steps, so the rainbow appears to turn. Each color is divided by 10, so the pixels run at a tenth of full brightness.

Parts list

3 parts, plus the jumper wires. They retail for about $13; on Mokxi they're free.

1 × ESP32-DevKitC V4
1 × Addressable RGB LEDsIn Claw Machine Kit, Halloween Prop Kit, Christmas Lights Kit.
1 × Power, 3.3 V

Kits that can build it

These 2 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
Addressable RGB LEDs pin DIN	ESP32-DevKitC V4 pin 2
Addressable RGB LEDs pin VDD	3.3 V
Addressable RGB LEDs pin VSS	Ground

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

# Rainbow: the color wheel spread across the eight pixels, turning one
# step at a time, at a tenth of full brightness.
from machine import Pin
import neopixel
import time

np = neopixel.NeoPixel(Pin(2), 8)

def wheel(pos):
    pos %= 255
    if pos < 85:
        return 255 - pos * 3, pos * 3, 0
    if pos < 170:
        pos -= 85
        return 0, 255 - pos * 3, pos * 3
    pos -= 170
    return pos * 3, 0, 255 - pos * 3

start = 0
while True:
    for i in range(8):
        r, g, b = wheel(start + i * 32)
        np[i] = (r // 10, g // 10, b // 10)
    np.write()
    start = (start + 4) % 255
    if start < 4:
        print("turn")
    time.sleep_ms(10)

Code walkthrough

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

`wheel` main.py

Takes a position and returns a red, green, blue triple. The wheel has three parts of 85 steps each. In each part, one color fades out while the next fades in, so the colors blend smoothly and loop back to the start.

def wheel(pos):
    pos %= 255
    if pos < 85:
        return 255 - pos * 3, pos * 3, 0
    if pos < 170:
        pos -= 85
        return 0, 255 - pos * 3, pos * 3
    pos -= 170
    return pos * 3, 0, 255 - pos * 3

Troubleshooting

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

The rainbow moves too fast or too slow. This project
Change the time.sleep_ms(10) pause or the step of 4 added to start.
The pixels are too dim. This project
The // 10 divides each color to a tenth. Use a smaller divisor for more brightness.
The first LED flickers, shows wrong colors, or the whole strip glitches. Addressable RGB LEDs
Join the grounds of the strip and the controller. Add a 300 to 500 ohm resistor in series with the data line. Put a 1000 uF capacitor across the strip's 5 V and GND.
The strip works at low brightness but dims, turns yellow, or resets when many LEDs go white. Addressable RGB LEDs
Each LED can draw about 60 mA at full white. Use a 5 V supply sized for the count, feed power in at several points, and lower the brightness in code.
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.