MQ9 gas sensor notes

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I already have bmp180 sensor connected to raspberry pi 3b+, now I want to add MQ9 sensor like this https://e-radionica.com/en/mq9-gas-sensor.html

  1. Is connection straight forward like the bmp180?
  2. Second question is how to wire mq9 to rpi with already connected bmp180?
  • “Precision” won’t matter much since you will be using the binary HIGH/LOW output as the Pi has no analog input — but in any case discussions about the precision of specific sensors is more appropriate to our larger sibling site, Electrical Engineering (so I have edited that out). – goldilocks 5 hours ago
  • Do you maybe know how high/low outputs are differentiated? – PostarLakogSna 5 hours ago
  • I believe the screw dial (gray circle w/ philips head “X”) controls this, but I could be wrong. – goldilocks 5 hours ago
  • @PostarLakogSna, Ah, let me see. Here is my quick and dirty MQ9 Rpi interface summary: (1) MQ9 is a digital guy, can be adjusted by the heating/timing and loading/sensitivity pots/resistors to trigger High logical alarm signal when gas (CO or flammable) leaking, (2) It is not connected to SPI or I2C bus like BMP180 or other sensors, so, no conflict between BMP and MQ work same time, (3) It is easy to connect MQ9 output pin (directly or after logical level shifting, or adding a chip Schmitt trigger chip to prevent false alarm) to Rpi GPIO pin in input mode. In short, – No worries at all! 🙂 – tlfong01 just now   Edit   


The BMP180 is a digital device and connects via the I2C bus.

The MQ9 is an analogue device and produces a variable voltage. It can not be directly connected to the Pi.

You need to connect the MQ9 to an ADC (Analogue to Digital Converter) and connect the ADC to the Pi.

ADCs tend to have an I2C or a SPI interface. The choice is yours.

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