The MQ-2 smoke or (Gas sensor) is sensitive to smoke and to the following flammable gases: LPG, butane, propane, methane, alcohol and hydrogen. The resistance across the sensor is different depending on the type of the gas. The smoke sensor has a built-in potentiometer that allows you to adjust the sensor digital output (D0) threshold. This threshold sets the value above which the digital pin will output a HIGH signal. 
| SENSOR PIN | ARDUINO CONNECTION |
| A0 | Any Analog pin |
| D0 | Any Digital Pin |
| GND | Ground with Arduino |
| Vcc | 5V |
WORKING DETAILS.
The voltage that the sensor outputs changes accordingly to the smoke/gas level that exists in the atmosphere. The sensor outputs a voltage that is proportional to the concentration of smoke/gas.
In other words, the relationship between voltage and gas concentration is the following:
The greater the gas concentration, the greater the output voltage The lower the gas concentration, the lower the output voltage. The output can be an analog signal (A0) that can be read with an analog input of the Arduino or a digital output (D0) that can be read with a digital input of the Arduino.
GAS SENSOR WITH ARDUINO:
In this example, you will read the sensor analog output voltage. When the smoke reaches a certain level, it will make sound a buzzer and a red LED will turn on. When the output voltage is below that level, a green LED will be on.
ALL SENSOR DETAILS:
1. HC-05 – Bluetooth
2. Mpu 6050 accelerometer-gyroscope- -module
3. Flame-sensor
4. Rotary-encoder
5. Force-sensor-fsr400
6. Current-sensor-acs712
7. Flex-sensor
8. IR-sensor-tcrt5000
9. Pulse-sensor-pin
10. Color-sensor-tcs230
11. SD-card-module
12. Oled-with-arduino
13. Addressable-rgb-led-strip-ws1812
14. Relay-module
15. TFT-1-8-display-st7735r
16. 8×8-dot-matrix-display-max7219
17. Smoke-sensor-mq-2
18. Ultrasonic-sensor-HC-sr04
19. PIR-motion-sensor-hc-sr501
20. Tilt-sensor-sw-520d
21. Microphone-sound-sensor
22. Reed-switch-reed-sensor
23. Rfid-reader-Em18
24. Rfid-tag
25. RTC-real-time-clock-ds1307
26. Temperature-sensor-ds18b20
27. Moisture-sensor
28. Rain-sensor
29. Pressure-sensor
30. Accelerometer
31. MOC-3021-circuit
32. DHT11-DHT22-temperature-and-humidity-sensor
CODE:
Upload the following sketch to your Arduino board (feel free to adjust the variable sensorThres with a different threshold value).
Copy and paste the Code into Arduino IDE.
int redLed = 5;
int greenLed = 6;
int buzzer =2;
int smokeA3 = A5;
// Your threshold value int sensorThres = 400;
void setup()
{
pinMode(redLed, OUTPUT);
pinMode(greenLed, OUTPUT);
pinMode(buzzer, OUTPUT);
pinMode(smokeA0, INPUT);
Serial.begin(9600);
}
void loop()
{
int analogSensor = analogRead(smokeA0);
Serial.print(“Pin A3: “);
Serial.println(analogSensor);
// Checks if it has reached the threshold value if (analogSensor > sensorThres)
{
digitalWrite(redLed, HIGH);
digitalWrite(greenLed, LOW);
tone(buzzer, 1000, 200);
}
else
{
digitalWrite(redLed, LOW);
digitalWrite(greenLed, HIGH);
noTone(buzzer);
}
delay(100);
}
Download Library: Here.
