How Can Rpi3B+ Detect MQ9 Gas Sensor's Carbon Monoxide Leakage,
Without Using ADC?
- Understanding MQ9's Digital and Analog signals
MQ9 has both a Digital and an Analog output signal, as summarized below:
(a) Digital - To detect gas leakage or no leakage, outputting High level 4.8V, or Low, 0.2V, respectively.
(b) Analog - To show gas intensity, outputting voltage in a range of 1.5V to 0.5V.
- Rpi reading MQ9's Digital and Analog Output
(a) Digital - Rpi can use a GPIO pin to read the MQ9 digital output, after converting logical level from 5V to 3V.
(b) Analog - Rpi must first use an ADC (Analog to Digital Converter) to convert MQ9 analog signal to digital, and then read the digital values.
- Calibrating MQ9 to detect Carbon Monoxide CO leakage
Only two simple steps. What you need is only a screw driver. No Rpi or even a multi-meter is needed to calibrate MQ9.
(a) Connect MQ9 to 5V.
(b) Adjust the 10k trim pot (trimming potentiometer), by trial and error, turning screw clockwise and counter clockwise, to locate the threshold triggering point when the alarm red LED turning on and off. Then turn screw a little bit anticlockwise to turn LED off. Now MQ9 is set to clean air.
- Testing MQ9's gas leaking alarm function
(a) Place MQ9 and a candle in a glass jar, and light the candle.
(b) After less then 2 minutes, the candle will burn out all the oxygen into carbon monoxide in the jar, and will extinguish, and red status LED will turn on.
- Writing a simple python program to read Rpi GPIO connected to MQ9
(a) Use a voltage divider to step down MQ9 5V logical level to 3V
(b) Connect MQ9 3V logical level output pin to any Rpi GPIO pin
(c) Write a simple python read GPIO program to finish off the project.
(1) MQ9 Gas Sensor - CO and Flamable GaSES - eRadionica €6
(2) MQ9 Gas Sensor Learning Notes V1.1 - tlfong01 2019nov04
(3) MQ9 Gas Sensor Testing Notes V1.1 - tlfong01 2019nov04
(4) Fibaro CO Sensor Discussion - StackExchange
(5) Fibaro CO Sensor Features - 100€
(6) ME2-CO Electrochemical Carbon Monoxide Sensor - WinSen Sensor
(7) AliExpress MQx Gas Sensor Catalog
Appendix A - Fibaro CO Sensor Features Summary
Make home safer and prevents danger caused from the ‘silent killer’
carbon monoxide (CO).
The sensor detects reliable carbon monoxide in the air and alarms in
case of exceeded limits.
Its high sensitivity allows to detect the presence of the carbon
monoxide (CO) gas at the early stage in order to prevent carbon
The device alarms via an integrated siren and blinking LED.
Additionally, automatic scenes can be triggered within the Z-Wave
gateway and notifications can be sent.
The FIBARO CO Sensor is a life-saving device, therefore tests to
conform compliance with the applicable requirements of the standard EN
50291-1:2010 are conducted by the BSI Group accredited testing
laboratory. Each sensor is subject to continuous control, which covers
routine product testing and the evaluation of manufacturing quality
CO sensor detects CO concentration in air
Alarm signalled with a LED diode
Supports protected mode (Z-Wave network security mode) with AES-128
May be used as stand-alone carbon monoxide detector
Wireless Technology: Z-Wave Plus
End of answer