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int waitTime;
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int startTime;
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int reactTime;
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void setup() {
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  Serial.begin(9600);
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  pinMode(13, OUTPUT);
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  pinMode(12, OUTPUT);
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  pinMode(11, OUTPUT);
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  pinMode(3, INPUT);
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}
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void loop() {
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  Serial.println("When the LED turns on, push the button!");
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  Serial.println("Now, watch the LED. Ready?");
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  waitTime = random(2000, 4000); //random wait time
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  delay(waitTime);  //delay random wait time
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  digitalWrite(13, HIGH);
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  startTime = millis();  //set zero time reference
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  //loop to wait until button is pressed
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  while(digitalRead(3) == HIGH) { }
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  reactTime = millis() - startTime; //calculation of reaction time
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  digitalWrite(13, LOW);  //turn off LED!
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  if (reactTime <= 215) {
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    digitalWrite(12, HIGH);  //green LED ON
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    digitalWrite(11, LOW);   //red LED OFF
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  }
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  else {
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    digitalWrite(12, LOW);   //green LED OFF
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    digitalWrite(11, HIGH);  //red LED ON
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  }
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  //display results
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  Serial.print("Nice job! Your reaction time was ");
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  Serial.print(reactTime);
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  Serial.println(" milliseconds");
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  //short delay before starting again
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  delay(5000);
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  digitalWrite(12, LOW);
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  digitalWrite(11, LOW);
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}