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Reaction-Time Game (Arduino)

Wait for the LED, then hit the button as fast as you can — the Arduino times you in milliseconds.

Beginner20 min

What you need

Wiring

Arduino Uno
LED
Push button

Hover a pin or a wire to trace the connection.

Code

reaction_game.ino
// Measure your reaction time: press the button when the LED lights.
const int ledPin = 13;
const int btnPin = 2;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(btnPin, INPUT_PULLUP);
  Serial.begin(9600);
  randomSeed(analogRead(A0));
}

void loop() {
  Serial.println("Get ready...");
  digitalWrite(ledPin, LOW);
  delay(random(2000, 5000));        // random wait so you can't cheat

  digitalWrite(ledPin, HIGH);       // GO!
  unsigned long start = millis();
  while (digitalRead(btnPin) == HIGH) { /* wait for press */ }
  unsigned long reaction = millis() - start;

  digitalWrite(ledPin, LOW);
  Serial.print("Reaction: ");
  Serial.print(reaction);
  Serial.println(" ms");
  delay(3000);
}

Steps

  1. Wire the LED on D13 (through 220Ω to GND) and the button on D2 to GND.
  2. Upload and open the Serial Monitor.
  3. When the LED lights, press the button as fast as you can — your time prints in ms.
  4. Don't jump early — the wait is randomized.