Photocell

A photocell can be used to detect light levels

A photocell (also called a light dependent resistor, LDR, or photoresistor) varies its resistance depending on the amount of light falling on it.

Wire up

Wire up the photocell using a 10kohm resistor like this:

Circuit	Pico
Red	3V3
Black	GND
Green	GP28 or another Analogue Pin

Code

Write this code and download to the Pico.

See code on github

# Test LDR (Light Dependent Resistor, sometimes called a photocell)

import time
import board
import analogio

#  Set up the LDR on pin 28 as an analogue input pin
photocell = analogio.AnalogIn(board.GP28_A2)

# Value will be 0 to 65535 (0 for bright, 65535 for dark or vice versa depending on the order of black/red wires)
while True:
    val = photocell.value
    print(val)
    time.sleep(.2)

Now vary the amount of light falling on the LDR and watch the output change.

Can you create a light (using an LED) that shines brighter when the light levels in the room fall?