MQ7 Gas sensor is another one of Metal Oxide Semiconductor (MOS) type Gas Sensor of MQ Gas Sensors family involving MQ 2, MQ 4, MQ 3, MQ 8, MQ 135, etc. It is mainly used to detect Carbon Monoxide. This sensor contains a sensing element, mainly aluminum-oxide based ceramic, coated with Tin dioxide (SnO2), enclosed in a stainless-steel mesh. Whenever CO gas comes into contact with the sensing element, the resistivity of the element changes. The change is then measured to get the concentration of the gases present. The MQ7 Sensor has a small heating element present which is needed to preheat the sensor to get it in the working window. It can detect Carbon Monoxide Gas in the range of 20 PPM to 2000 PPM in the air. It finds uses in Alarm application in case of CO gas concentration build-up in the home or your car as CO is a very harmful gas and can kill a person if present over 300PPM.

 Specifications:

• Operating Voltage is +5V
• Can be used to Measure or detect CO
• Analog output voltage: 0V to 5V
• Digital Output Voltage: 0V or 5V
• Stable, Long life and Low Cost
• Fast Response time
• Heater consumption about 350mW
• The Sensitivity of Digital Output pin can be varied using the potentiometer

To use the Sensor Module, you have power the device with 5V supply and the Power LED will start to glow. To power it, you can use external supply or connect +5V and GND pin of Arduino. You should give it some preheating time before start reading the output. While measuring the gas present, the Output LED will glow in a specific concentration of the gas. You can change it by using the potentiometer. Else you can also use the Analog Output to see how your program reacts to different concentrations of gases present.