Reaction Game: Random Wait

Part of the Projects section of Coddy's Arduino journey. Lesson 5 of 24.

The next project is a reaction game. You press the button, the board waits, then lights the LED, and you press again as fast as you can.

The wait is random, or you would learn the rhythm. random(1000, 3001) gives a whole number from 1000 to 3000.

random() is a calculation: after every power-on it gives the same numbers in the same order. randomSeed() picks where that sequence starts. Seed it with the moment of the press, in microseconds, which is different every game:

randomSeed(micros());
waitTime = random(1000, 3001);

The game is a state machine with three states: READY (waiting for a press), WAITING (the random wait) and LIT (the LED is on). The wait uses millis(), so later steps can watch the button during it.

The starter already works out pressed: the button reads LOW now and read HIGH last time. This button does not bounce, so it needs no debounce.

Challenge

Medium

The button is on pin 2 and the LED on pin 12. Fill in the three states:

READY: a press seeds with micros(), picks a wait of 1000 to 3000 ms, saves the start time, moves to WAITING
WAITING: when the wait is over, light the LED and move to LIT
LIT: a press turns the LED off and moves to READY

Press Run, play a few rounds, then Check.

Try it yourself

const int ledPin = 12;
const int buttonPin = 2;

// The three states of a round
enum State { READY, WAITING, LIT };
State state = READY;

int lastButton = HIGH;       // the button reading the last time
unsigned long waitStart = 0; // when the wait began
unsigned long waitTime = 0;  // how long this wait lasts

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  Serial.begin(9600);
  Serial.println("Press the button to start");
}

void loop() {
  int button = digitalRead(buttonPin);
  bool pressed = (button == LOW && lastButton == HIGH);  // pressed just now
  lastButton = button;

  // READY: a press starts the wait
  // WAITING: when the wait is over, light the LED
  // LIT: a press turns the LED off and the game is ready again

}

Test yourself

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

All lessons in Projects

Practice on your own: Arduino playground