Hi all,
I had a query regarding the MQ class gas sensors, regarding the actual wiring of the pins. The data sheet is clear that pins 2 and 5 are the power pins however it does not mention which ones are the data output pins, as it simply mentions not to power and ground 1,3 - 4,6 respectively. However in the wiring example it shows that MQ135 a completely different sensor from the same class with similarly 6 pins being wired up with three pins connected to power, two to ground with a pulldown resistor and another data output. If this is true for MQ7 specifically which pin do i use to regulate the voltage from 1.4 V to 5 V, as there’s only one data output pin listed.
TLDR, whats the correct method to wire up the 6 pins ? for MQ7 specifically
Cheers,
Glen
Hello Pathfinder4,
As for the MQ-7 Pins specifically, I would recommend:
Pin 2 => +5V while in standby (+1.5V in active)
Pin 5 => GND
Pin 6 = Pin 4 => 5V
Pin 1 = Pin 3 => in-series resitor (RL in datasheet)
RL => GND
As for the ‘Wiring Example’ that states “MQ135”, that configuration is also correct. It seems the ‘analog’ pin is either pin 1 or 3 which groups to the same ‘section’ of the sensor. The difference between the MQ-135 and MQ-7 seems to be that the MQ-7 heater voltage should be bucked to 1.5V during measuring.
My strongest suggestion would be unit testing as much as possible before developing a final version of your project. It would even be helpful looking at [Pololu’s Resources for this sensor.
The level of support I can provide past this is limited, but I hope this helps point you in the right direction. Best of wishes on your project.](Pololu - Carbon Monoxide Gas Sensor MQ-7)