Solar panel tracker with two LDRs

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 gpiozero import LightSensor, AngularServo
from time import sleep

left = LightSensor(4)
right = LightSensor(5)
panel = AngularServo(18, min_angle=-90, max_angle=90)

angle = 0
panel.angle = angle

while True:
    error = right.value - left.value          # positive: right side is brighter
    if abs(error) > 0.1:                      # a dead band stops jitter
        angle += 5 if error > 0 else -5
        angle = max(-90, min(90, angle))      # stay inside the servo range
        panel.angle = angle
    print("Left %.2f  Right %.2f  Panel %d deg" % (left.value, right.value, angle))
    sleep(0.5)

How the code works

• error is the difference between right and left light. Zero means the panel faces the sun.
• The panel moves 5 degrees at a time towards the brighter side. That is a simple feedback loop.
• The dead band of 0.1 stops the servo from shaking when both sensors are nearly equal.
• max() and min() keep the angle between -90 and +90.

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.