Automatic Night Light

Part of the Inputs section of Coddy's Arduino journey. Lesson 13 of 22.

A photoresistor is a resistor whose value changes with light: the more light falls on it, the lower its resistance. This one sits on a small module with four pins: VCC and GND for power, AO (analog out) and DO (digital out).

AO gives a voltage you read with analogRead(). On this module it falls as the light rises: about 1023 in the dark, close to 0 in bright light. So a big reading means dark.

int reading = analogRead(A0);
if (reading > 600) {
  // dark
}

On the board, the slider on the sensor sets how much light falls on it.

Challenge

Easy

The light module's AO is on A0 and an LED on pin 13. Make a night light:

read A0 and print the reading, then wait 100 ms
light the LED when the reading is above 600 (dark), otherwise turn it off

Press Run, move the light slider, then Check.

Try it yourself

const int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // read the light module on A0 and print the reading
  // light the LED when it is dark (reading above 600)
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Inputs

Practice on your own: Arduino playground