Air Conditioner Compressor Status Sensor

I finally turned my compressor status circuit into a nice looking PCB. This sensor monitors the control lines between the inside unit of my air conditioner and the compressor outside. My unit has a two stage compressor and with this I can track if it is off, or running in stage 1 or stage 2. This allows me to locally track every time the compressor turns on, in spite of the Lennox cloud. The Lennox thermostat doesn’t report the system running when it is just running to dehumidify, plus the cloud connection fails occasionally so in both instances, I miss data. There is nothing Lennox specific about this so it should work on any spit unit AC that uses 24V signaling.


This device is a shield for the Wemos D1 mini and reports status over MQTT. I previously used the GarHAge code @marthocoo wrote for my garage door circuit, so I stripped out the control side of his code and used it for this as well. It is a little complicated for this simple sensor but why write code when someone already did a great job.


I posted the eagle files and gerbers on GitHub if someone wants to make their own or expand on it. I don’t have the part list in the repository yet but I will add that soon. If you need help just ask. I am enjoying the design and construction as much as the ability to automate and collect data! There is one thing on this board I want to tweak but so far that is lower priority than other projects.


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OK, the board has been tweaked, a local library for the parts was created and I have a complete BOM all added to GitHub. For the board tweaks I moved the right chip to the left a bit as it was really easy to create a solder bridge with the terminal pad. I also made a few updates to the silkscreen to make things clearer.