Cycle Modes With a Button

Part of the Timing Without Delay section of Coddy's Arduino journey. Lesson 11 of 18.

Many gadgets have one button that steps through modes: a bike light goes off, on, blinking, fast blinking, then off again. That is a state machine where a press, not the clock, moves to the next state.

Put the step in its own function. A switch on the current mode sets the next one, and the last mode goes back to the first:

void nextMode() {
  switch (mode) {
    case OFF:
      mode = ON;
      Serial.println("ON");
      break;
    // ... and so on, until FAST goes back to OFF
  }
}

The sketch calls nextMode() once per press. The button is debounced the way you learned in the Inputs section: when the reading changes, act on it, then wait 20 ms for the contacts to settle. A second switch on mode sets the LED.

Challenge

Medium

The button and the LED are written for you. Write nextMode() so each press moves to the next mode and prints its name: OFF, ON, BLINK, FAST, then OFF again.

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

Try it yourself

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

enum Mode { OFF, ON, BLINK, FAST };
Mode mode = OFF;

bool wasPressed = false;
unsigned long blinkPrevious = 0;
int ledState = LOW;

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

// Moves to the next mode and prints its name.
void nextMode() {
  // one case per mode: set the next mode, print its name, break
}

// Switches the LED every interval ms.
void blinkEvery(unsigned long interval) {
  unsigned long now = millis();
  if (now - blinkPrevious >= interval) {
    blinkPrevious = now;
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;
    }
    digitalWrite(ledPin, ledState);
  }
}

void loop() {
  // 1. a press (debounced) calls nextMode()
  bool pressed = digitalRead(buttonPin) == LOW;
  if (pressed != wasPressed) {
    if (pressed) {
      nextMode();
    }
    wasPressed = pressed;
    delay(20);   // let the contacts settle
  }

  // 2. the mode decides what the LED does
  switch (mode) {
    case OFF:
      digitalWrite(ledPin, LOW);
      break;
    case ON:
      digitalWrite(ledPin, HIGH);
      break;
    case BLINK:
      blinkEvery(500);
      break;
    case FAST:
      blinkEvery(100);
      break;
  }
}

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 Toggles A 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 MachineCycle 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