2 · Inputs & sensors
Light sensor (LDR)
Intermediate15 min
Goal
Turn the LED on automatically when the room gets dark.
Why it matters
The voltage divider turns a variable resistance into a measurable voltage.
Steps
- 01Add a light sensor on A0.
- 02Pick a threshold (e.g. 400) and compare it to the reading.
- 03Light the LED below the threshold, switch it off above.
- 04Change the light level in the Scenario panel while running.
This tutorial runs inside the Circuitly simulator: your wiring and your code are checked automatically at every step.
Next tutorials
- Read a push button
Light the LED only while the button is pressed.
- Toggle button (debounced)
One press turns on, the next turns off — with no contact bounce.
- Read a potentiometer
Print the analog value of A0 on the serial monitor.
- Convert to volts (map & float)
Turn the ADC's 0–1023 into a 0.00–5.00 V reading.