MQ-7 module consists of the MQ-7 CO sensor IC with Carbon Monoxide as a gas sensing element. MQ-7 sensor is ideal for detection or measuring of carbon monoxide concentration at a range from 10 to 10000ppm in air. It offers excellent sensitivity and fast response makes it ideal for portable gas detectors or in other industrial applications. The module comes with basic components integrated allowing the sensor to function properly. And interfaced easily to any controller as the user prefers. Hence no external components required, we need to just plug in Vcc & ground pins and you are ready to go.
MQ7 is a Tin oxide semiconductor sensor designed explicitly for Carbon Monoxide (CO) concentration detection. It works by detecting the CO concentration of cycle high and low temperature, and detect CO at low temperature (heated by 1.5V). An analog resistive output provided by the sensor with conductivity higher along with the gas concentration rising. The resistance varies inside the sensor on the detection of carbon monoxide. Under the high temperature (heated by 5.0V), the other gases adsorbed under the low temperature cleared. We just need to power the heater coil with 5V, add a load resistance. As a result, the sensor and load resistor in the module form a potential divider and connect the output to an ADC or a simple OPAMP comparator.
Thus the CO content detected by measuring this resistance. Therefore the lower the sensor resistance, the upper the voltage reading is going to be. MQ7 sensor designed to operate at temperatures ranging from -10 to 50°C. And consumes less than 150 mA current at 5 V.