const int redPin = 18;
const int greenPin = 19;
const int bluePin = 21;
const int potPin = 34;

void setup() {
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
}

void loop() {
  int potValue = analogRead(potPin);

  if (potValue < 1700) {
    // Blink RED
    digitalWrite(redPin, HIGH);
    digitalWrite(greenPin, LOW);
    digitalWrite(bluePin, LOW);
    delay(500);
    digitalWrite(redPin, LOW);
    delay(500);
  }
  else if (potValue < 3400) {
    // Blink GREEN
    digitalWrite(greenPin, HIGH);
    digitalWrite(redPin, HIGH);
    digitalWrite(bluePin, LOW);
    delay(500);
    digitalWrite(greenPin, LOW);
    delay(500);
  }
  else {
    // Blink BLUE
    digitalWrite(bluePin, HIGH);
    digitalWrite(redPin, LOW);
    digitalWrite(greenPin, LOW);
    delay(500);
    digitalWrite(bluePin, LOW);
    delay(500);
  }
}