gistfile1.c

// give it a name:
int _led = D7;

//function definition
int led(String command);

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(_led, OUTPUT);  
  Spark.function("led", led);
}

// the loop routine runs over and over again forever:
int led(String command) {

  if(command == "ON") {    
      digitalWrite(_led, HIGH);   // turn the LED on (HIGH is the voltage level)
  } else {
      digitalWrite(_led, LOW);   // turn the LED off 
  }

  return 1;
}

void loop() {
    
}