int mq3 = A0; 
int buzzer = 7;
int red_led = 8;
int green_led = 9;
int threshold =300; 
void setup(){
   Serial.begin(9600); 
   pinMode(red_led, OUTPUT);
   pinMode(green_led, OUTPUT); 
   pinMode(buzzer, OUTPUT); 
   digitalWrite(red_led, LOW);
   digitalWrite(green_led, LOW); }
 
void loop()
{
    int mq3 = analogRead(mq3);
    Serial.println(mq3);
    if(mq3>=threshold){
        digitalWrite(red_led,HIGH);
        digitalWrite(green_led,LOW);
        tone(buzzer,200);
        Serial.println(" Dikkat Uyarı!!!");
        delay(1000);
    }
    else{
        digitalWrite(red_led,LOW);
        digitalWrite(green_led,HIGH);
        noTone(buzzer);
    }
    delay(100); 
}