char incomingByte = 0; // for incoming serial data #define PIN 7; // Analog output pin that the diffuser is attached to
void setup() {
  Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
  pinMode(7,OUTPUT);
  //#define PIN 7; // Analog output pin that the diffuser is attached to

}

void loop() {
  // send data only when you receive data:
  if (Serial.available() >= 0) {
    // read the incoming byte:
    incomingByte = Serial.read();
    if (incomingByte == '1'){
      digitalWrite(7,HIGH);      
    }
    else if (incomingByte == '0'){
      digitalWrite(7,LOW);
    }
  }
}