User Manual

108
Lesson 22 Gas Sensor
Introduction
Gas Sensor MQ-2 is a sensor for flammable gas and smoke by detecting the concentration
of combustible gas in the air. They are used in gas detecting equipment for smoke and
flammable gasses in household, industry or automobile.
Components
- 1 * Raspberry Pi
- 1 * Breadboard
- 4 * Jumper wires (Male to Male, 2 red and 2 black)
- 1 * Network cable (or USB wireless network adapter)
- 1 * Active Buzzer module
- 1 * PCF8591
- 1 * Gas sensor module
- 1 * 3-Pin anti-reverse cable
- 1 * 4-Pin anti-reverse cable
- Several Jumper wires (Male to Female)
Experimental Principle
MQ-2 gas sensor is a kind of surface ion type and N-type semiconductors, which uses tin
oxide semiconductor gas sensitive material. When ambient temperature is in 200 ~ 300℃, tin
oxide will adsorb oxygen in the air and form oxygen anion adsorption to decrease electron
density in semiconductor so as to increase its resistance. When in contact with the smoke, if
grain boundary barrier is modulated by the smoke and changed, it could cause surface
conductivity change. So you can gain the information of the smoke existence, The higher
the smoke concentration is, the more conductive the material becomes, thus the lower the
output resistance is.
In this experiment, if harmful gases reach a certain concentration, the buzzer will beep to
warn.