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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 7 hours ago
  • Do you maybe know how high/low outputs are differentiated? – PostarLakogSna 7 hours ago
  • I believe the screw dial (gray circle w/ philips head “X”) controls this, but I could be wrong. – goldilocks 7 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 2 hours ago   
  • @PostarLakogSna, Please let me know if your MQ9 module is similar to mine: imgur.com/gallery/MqXE3CH. or give me the link of yours (same as in your question?). Perhaps I can try to do some engineering experimentation for. MQ9 is a life critical thing, and I am just a friendly home automation hobbyist, so do ask for a professional opinion! 🙂 – tlfong01 2 hours ago    
  • @PostarLakogSna, You might also like to let me know if you wish to measure (1) Digital, (2) Analog, (3) PPM, (4) All above three together. To do analog or ppm, you need an ADC。 For, analog measurement, you can do early warning risk analysis before the red alarm alert trigger level is reached. For ppm, you can also recognize which type of gas is present, and send messages to you android smart phone, indicating level of risk etc. Below is my engineering experimentation log entry: penzu.com/p/93aaa16e This linked engineering experimentation report keeps updating, so stay “tuned” 🙂 – tlfong01 1 hour ago   
  • @PostarLakogSna, PPM measurement is interesting. The circuit is not that complicated. You can use the very popular Rpi friendly MCP3008 10 bit SPI ADC (Google AdaFruit or SparkFun for newbie friendly tutorials): Connect MQ9 Load resistor analog output to MCP3008, which in turn is connected to Rpi SPI. You can use colourful LEDs connected Rpi GPIO pins to indicate which type of gas is detected, or LED bars to indicate gas intensity etc . The ppm measurement tutorial: “How to Choose GAS sensor?” – theorycircuit.com. theorycircuit.com/choose-gas-sensor, Happy reading. Cheers! 🙂 – tlfong01 2 mins ago    Edit   

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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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