Automatic night lamp

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, LED
from signal import pause

ldr = LightSensor(4, threshold=0.3)     # dark when below 30 %
lamp = LED(17)

def dark():
    lamp.on()
    print("It is dark: lamp ON")

def light():
    lamp.off()
    print("It is light: lamp OFF")

ldr.when_dark = dark
ldr.when_light = light

print("Drag the Daylight slider below 30 %")
pause()

How the code works

• An LDR has low resistance in light and high resistance in the dark. With a capacitor, the Pi times how fast the pin charges.
• LightSensor turns that timing into a value from 0 (dark) to 1 (bright).
• when_dark and when_light run your functions when the value crosses the threshold.

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.