Toggle on Each Press

Part of the Inputs section of Coddy's Arduino journey. Lesson 4 of 22.

So far the LED has copied the button: on while held, off when let go. A lamp switch works differently: press once for on, press again for off. That is a toggle.

To toggle, the sketch must notice the moment the button goes down: pressed now, but not pressed the last time loop() ran. That moment is called an edge. Keep the last reading in a variable above setup(), like a counter:

int lastReading = HIGH;

void loop() {
  int reading = digitalRead(2);
  if (reading == LOW && lastReading == HIGH) {
    // the button has gone down
  }
  lastReading = reading;
}

Holding the button keeps the reading LOW, so the edge happens once per press, however long you hold it.

To flip a bool, use !, which means "not": ledOn = !ledOn; turns true into false and back.

Challenge

Medium

The button is on pin 2 (INPUT_PULLUP) and the LED on pin 13. Make each press toggle the LED:

when the button goes down (LOW now, HIGH last time), flip ledOn
save the reading in lastReading at the end of loop()
turn the LED on or off to match ledOn

Press Run, press the button a few times, then Check.

Try it yourself

const int buttonPin = 2;
const int ledPin = 13;

bool ledOn = false;
int lastReading = HIGH;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  int reading = digitalRead(buttonPin);
  // flip ledOn when the button goes down
  // remember this reading for next time
  // turn the LED on or off to match ledOn
}

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