Colour detector with three LEDs

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from picamera2 import Picamera2
from gpiozero import LED
from time import sleep

cam = Picamera2()
cam.configure(cam.create_preview_configuration())
cam.start()
sleep(1)

leds = {"red": LED(17), "green": LED(27), "blue": LED(22)}
last = None

while True:
    frame = cam.capture_array()
    seen = "nothing"
    for name, led in leds.items():
        if frame.find_color(name):
            led.on()
            seen = name
        else:
            led.off()
    if seen != last:                  # print only when it changes
        print("I see:", seen)
        last = seen
    sleep(0.3)

How the code works

• leds is a dictionary: the name "red" belongs to the LED on GPIO17.
• The for loop asks the camera picture about each colour in turn and switches the matching LED.
• seen and last make the console quiet: it prints a line only when the colour changes.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.