A Light on a Timer

Part of the Timing Without Delay section of Coddy's Arduino journey. Lesson 6 of 18.

A stairway light comes on when you press its button and goes off by itself a little later. Press again while it is on, and the time starts over.

That needs two things: the moment of the last press, and whether the light is on. Store the moment in an unsigned long when the button is down:

if (digitalRead(buttonPin) == LOW) {
  pressedAt = millis();     // start (or start again) the time
  lightOn = true;
  digitalWrite(ledPin, HIGH);
}

Then, on every loop, check how long it has been:

if (lightOn && millis() - pressedAt >= onTime) {
  lightOn = false;
  digitalWrite(ledPin, LOW);
}

The two parts never wait, so a press is seen at any moment, even while the light is already on. With delay(2000) after the press, a second press during the wait would be lost.

Challenge

Easy

Build a stairway light:

a press lights the LED on pin 13 at once
2 seconds after the press, it goes off by itself
a press while it is on starts the 2 seconds again

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

Try it yourself

const int ledPin = 13;
const int buttonPin = 2;
const unsigned long onTime = 2000;   // how long the light stays on

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

void loop() {
  // when the button is down: light the LED and remember the time

  // when onTime has passed since then: turn the LED off
}

Test yourself

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

All lessons in Timing Without Delay

1millis()

The millis() Clock Times in unsigned long Blink Without Delay Two LEDs, Two Speeds Blink While a Button TogglesA Light on a Timer

4Precise Timing

Measure With micros()When millis() Rolls Over Button Stopwatch

2State Machines

Remember the Mode Choosing With switch Named States With enum Traffic Light State Machine Cycle Modes With a Button

3Interrupts

A Press the Loop Misses FALLING, RISING and CHANGE Sharing With volatile Count Presses by Interrupt

Practice on your own: Arduino playground