Automatic porch light

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 MotionSensor, LightSensor, OutputDevice
from time import sleep, time

pir = MotionSensor(22)
ldr = LightSensor(4)
lamp = OutputDevice(17, active_high=False)

DARK_BELOW = 0.3       # darker than 30 % light
HOLD = 8               # keep the lamp on for 8 seconds
off_at = 0

print("Set Daylight below 30 % and click the PIR dome")
while True:
    is_dark = ldr.value < DARK_BELOW
    if is_dark and pir.motion_detected:
        if not lamp.value:
            print("Dark and movement: lamp ON")
        lamp.on()
        off_at = time() + HOLD            # restart the timer
    if lamp.value and time() > off_at:
        lamp.off()
        print("Timer finished: lamp OFF")
    sleep(0.2)

How the code works

• The lamp needs both facts to be true: it is dark (ldr.value is low) and there is movement (the PIR output is high).
• Each time movement is seen, off_at is moved forward by HOLD seconds. The lamp only goes off when the time passes off_at.
• The loop checks five times a second. sleep(0.2) keeps the page and a real Pi relaxed.

Parts to buy

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