#define GREEN 10 //defining pins #define RED 11 void setup(){ pinMode(GREEN, OUTPUT); //setting pins as outputs pinMode(RED, OUTPUT); Serial.begin(9600); //start serial communication @9600 bps } void loop(){ if(Serial.available()){ //if serial communication is available, char val = Serial.read(); //respectively reads if(val == 'g'){ //..if Arduino reads 'g', turn on LED on pin 10 digitalWrite(GREEN, LOW); } if(val == 'r'){ //..if Arduino reads 'r', turn on LED on pin 10 digitalWrite(RED, LOW); } if(val == 'f'){ //..if Arduino reads 'f', turn off LEDs on pin 10, 11. digitalWrite(GREEN, HIGH); digitalWrite(RED, HIGH); } } }