Named States With enum

Part of the Timing Without Delay section of Coddy's Arduino journey. Lesson 9 of 18.

A mode numbered 0, 1 and 2 works, but if (mode == 2) does not say what 2 means. An enum gives each number a name:

enum State { READY, RUNNING, DONE };
State state = READY;

The first line makes a new type, State, whose only values are READY, RUNNING and DONE. Underneath they are still 0, 1 and 2, but the names say what each one means. The second line makes a variable of that type.

An enum and a switch fit together: one case per state.

switch (state) {
  case READY:
    // what READY does, and when it moves on
    break;
  case RUNNING:
    // ...
    break;
}

To move to a new state, set state and remember when it began: state = DONE; stateStart = millis();. Each state then times itself with millis() - stateStart. This way of writing a sketch is called a state machine.

Challenge

Medium

A machine has three states. READY is written for you: the green LED is on, and a press starts the machine. Add the other two cases:

RUNNING: the yellow LED is on. After 2000 ms, turn it off and go to DONE.
DONE: the red LED is on. After 1000 ms, turn it off and go back to READY.

Store stateStart on each change. Press Run, press the button, then Check.

Try it yourself

const int buttonPin = 2;
const int greenLed = 10;
const int yellowLed = 11;
const int redLed = 12;

enum State { READY, RUNNING, DONE };
State state = READY;

unsigned long stateStart = 0;   // when the current state began

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(greenLed, OUTPUT);
  pinMode(yellowLed, OUTPUT);
  pinMode(redLed, OUTPUT);
}

void loop() {
  unsigned long now = millis();

  switch (state) {
    case READY:
      digitalWrite(greenLed, HIGH);
      if (digitalRead(buttonPin) == LOW) {
        digitalWrite(greenLed, LOW);
        state = RUNNING;
        stateStart = now;
      }
      break;

    // add case RUNNING: yellow on; after 2000 ms, yellow off and go to DONE

    // add case DONE: red on; after 1000 ms, red off and go back to READY
  }
}

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 switchNamed States With enumTraffic 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