#define MQ2_ANA A4
#define MQ2_DIG 2

void setup() {
  Serial.begin(9600);
  pinMode(MQ2_ANA, INPUT);
  pinMode(MQ2_DIG, INPUT);
  pinMode(8, OUTPUT);
  pinMode(7, OUTPUT);
}

void loop() {
  int val = analogRead(MQ2_ANA);
  int state = digitalRead(MQ2_DIG);
  Serial.print("Analog: ");
  Serial.println(analogRead(MQ2_ANA));
  if (state == HIGH){
      for(int i=1000;i<2000;i+=3){
      tone(7,i);
      digitalWrite(8,i);
      delay(1);
}
    for(int i=2000;i>1000;i-=3){
      tone(7,i);
      digitalWrite(8,i);
      delay(1);
  }
}
else {
  tone(7,0);
  digitalWrite(8, LOW);
  }
}