MQ-2
Sensitive for Methane, Butane, LPG, smoke.
This sensor is sensitive for flamable and combustible gasses.
MQ-3
Sensitive for Alcohol, Ethanol, smoke
The MQ303A (also on this page) is like this sensor, but uses a lower heater voltage.
MQ-4
Sensitive for Methane, CNG Gas
MQ-5
Sensitive for Natural gas, LPG
MQ-6
Sensitive for LPG, butane gas
The MQ306A (also on this page) is like this sensor, but uses a lower heater voltage.
MQ-7
Sensitive for Carbon Monoxide
The MQ307A (also on this page) is like this sensor, but uses a lower heater voltage.
MQ-8
Sensitive for Hydrogen Gas
MQ-9
Sensitive for Carbon Monoxide, flammable gasses.
The heater uses an alternating voltage of 5V and 1.5V. It depends on the gases how to use that alternating voltage. If only Carbon Monoxide is tested, the heater can be set at 1.5V.
The MQ309A (also on this page) is like this sensor, but uses a lower heater voltage.
MQ131
Sensitive for Ozone
The heater uses 6V.
The load-resistor is 100k...200k, which is a lot higher than for other sensors. This sensor is also very sensitive. It measures in ppb (parts per billion) where other sensors measure in ppm (parts per million).
MQ135
For Air Quality
Sensitive for Benzene, Alcohol, smoke.
An example with calculation of the CO2 value: http://davidegironi.blogspot.it/2014/01 ... -with.html
MQ136
Sensitive for Hydrogen Sulfide gas.
MQ137
Sensitive for Ammonia.
MQ138
Sensitive for Benzene, Toluene, Alcohol, Acetone, Propane, Formaldehyde gas, Hydrogen gas.
MQ214
Sensitive for Methane, Natural gas.
The heater uses 6V.
MQ216
Sensitive for Natural gas, Coal gas.
MQ303A
Sensitive for Alcohol, Ethanol, smoke (just like the MQ-3)
The heater uses 0.9V
MQ306A
Sensitive for LPG, butane gas
The heater uses 0.9V.
It detects the same gasses as the MQ-6, but uses a lower heater voltage.
MQ307A
Sensitive for Carbon Monoxide
The heater uses an alternating voltage of 0.2V and 0.9.
It detects the same gasses as the MQ-7, but uses a lower heater voltage.
MQ309A
Sensitive for Carbon Monoxide, flammable gasses.
The heater uses an alternating voltage of 0.2V and 0.9V. It depends on the gases how to use that alternating voltage.
It detects the same gasses as the MQ-9, but uses a lower heater voltage.