Colour tracker that points a servo

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 AngularServo
from time import sleep

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

servo = AngularServo(18, min_angle=-90, max_angle=90)

while True:
    frame = cam.capture_array()
    spot = frame.find_color("red")       # (x, y, area) or None
    if spot is None:
        print("No red ball in view")
    else:
        x, y, area = spot
        fraction = x / frame.width       # 0 = far left, 1 = far right
        servo.angle = -90 + fraction * 180
        print("Ball at %3d %%  ->  servo %4d degrees" % (fraction * 100, servo.angle))
    sleep(0.2)

How the code works

• find_color("red") looks for red pixels and gives their centre. It gives None when it finds nothing.
• The yellow cross on the camera view shows what the program found.
• x / frame.width turns the position into a number from 0 to 1 that does not depend on the picture size.
• -90 + fraction * 180 maps 0 to 1 onto -90 to +90 degrees.

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.