Light Sensor Switch Pin

Part of the Inputs section of Coddy's Arduino journey. Lesson 14 of 22.

The light module has a small chip of its own, a comparator, that does the threshold for you. It compares the light with a level set by the little screw on a real module and drives the DO pin: LOW when it is bright, HIGH when it is dark. On this board the level is half light.

DO is a digital signal, so you read it like a button, with digitalRead(). The module drives the pin itself, so it needs no pull-up: a plain INPUT is right.

pinMode(7, INPUT);

if (digitalRead(7) == HIGH) {
  // dark
}

To print a message only when the light changes, use the edge idea from the button lessons: compare the reading with the one from last time.

Challenge

Easy

The module's DO is on pin 7 and the LED on pin 13:

set pin 7 to INPUT
light the LED while DO is HIGH (dark), otherwise turn it off
when the reading changes, print Dark or Bright

Press Run, move the light slider past the middle both ways, then Check.

Try it yourself

const int sensorPin = 7;
const int ledPin = 13;

int lastDark = LOW;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
  // set the sensor pin to INPUT
}

void loop() {
  // read DO, light the LED in the dark
  // print Dark or Bright when the reading changes
}

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