// Arduino and KY-036 module
 
void setup ()
{
pinMode (13, OUTPUT); // built-in LED pin set to output
pinMode (8, INPUT); // module digital output connected to Arduino pin 8
Serial.begin(9600); // initialize serial
}
 
void loop ()
{
// display analog and digital values to serial
Serial.print("Analog pin: ");
Serial.print(analogRead(A0));
 
Serial.print(" | Digital pin: ");
 
if (digitalRead(8) == HIGH) {
Serial.println("High");
digitalWrite (13, HIGH); // if module value is higher than threshold,
// switch-On built-in LED
}
else {
Serial.println("Low");
digitalWrite (13, LOW);
}
 
delay(100); // wait 100 milliSeconds
}

• Normal air returns approximately 100-150
• Alcohol returns approximately 700
• Lighter gas returns approximately 750

#include <LiquidCrystal.h>
int sensorValue;
const int rs = 12, en  = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
void  setup(){  lcd.begin(16, 2);
Serial.begin(9600);                            //  sets the serial port to 9600
 }
void loop(){sensorValue = analogRead(0);       //  read analog input pin 0
Serial.print("AirQua=");
Serial.print(sensorValue,  DEC);               // prints the value read
Serial.println(" PPM");
lcd.setCursor(0,0);
lcd.print("ArQ=");
lcd.print(sensorValue,DEC);
lcd.print("  PPM");
lcd.println("       "); 
lcd.print("  ");
delay(100);                                   //  wait 100ms for next reading
}

• MQ-135 Gas Sensor Technical Data