I recently set up a home monitoring station using a Pi Zero W and a [Pimoroni Enviro+ and want to add some carbon monoxide monitoring to my setup. I found the MQ-7 and the itty bitty [Sparkfun gas sensor breakout. After some investigation, I discovered the MQ-7 needs a 5v ADC and the onboard ADC on the enviro+ only has a 3v ADC. No problem, Pimoroni sell the[ ADS1015 ADC on a breakout board (I guess this will work?)
However, the labelling of the pins on the two boards don’t quite match up.
On the Pimoroni ADC we have pins labelled 3-5V, A0, A1, A2 and GND
On the Sparkfun breakout board, we have GND, B1, H1 and A1
Can anyone please help me connect the dots? Cheers!
H1 and GND are the connections for the heater and that runs at 5 volts. These ONLY power the heater and don’t influence the other terminals on the board.
A1 and B1 are the two ends of the sensor and you can think of the sensor as a simple variable resistor. What you need to do is create a voltage divider with an external resistor and the “variable resistor” that’s inside the sensor and then measure the voltage at the connection between the two resistors.
As long as you have 5 volt and 3 volt power available, you can power the heater with 5 volts and connect 3 volts to your voltage divider. That will eliminate the need for an ADC that is 5 volt capable.
Thanks for the reply Chris! For some reason I don’t have permission to see the image you posted, but I’m assuming the solution looks something like this?
You should be able to click on the text in my post that says “08891-SparkFun_Gas_Sensor_Breakout-02.jpg” to view the image. You do need to be logged into the forum in order to see the image though.
Give it another go and see if you’re able to view it, if not let me know and I’ll see if I can post it another way.
