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This example is for Wiring version 1.0 build 0100+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

Functions.
The trafficLight() turns ON the specified light and waits 2 seconds. Each call to trafficLight() specifies the pin in which a color LED is connected, turns OFF all colors and then turn ON the one specified

    int RED = 8;
    int YELLOW = 9;
    int GREEN = 10;

    void setup()
    {
      pinMode(RED, OUTPUT);
      pinMode(YELLOW, OUTPUT);
      pinMode(GREEN, OUTPUT);
    }

    void loop()
    {
      trafficLight(RED);
      trafficLight(YELLOW);
      trafficLight(GREEN);
    }

    void trafficLight(int color)
    {
      // turn OFF all lights
      digitalWrite(RED, LOW);
      digitalWrite(YELLOW, LOW);
      digitalWrite(GREEN, LOW);
      // turn ON the one received
      digitalWrite(color, HIGH);
      delay(2000);
    }