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Originally Posted by jeff5may
The tool you seek here is a logic analyzer. There are literally a jillion of these things on the market to suit many needs. In this case, the hrv controller probably runs in the single digit MHz range, and comms much slower. A cheap, USB-based probe will more than do the job here. Just search for "usb logic analyzer" or "pc logic oscilloscope" and the like. If the unit does indeed chat back and forth, it probably speaks i2c, spi, or some other common language. There are open-source interpreter programs on the web that can help you figure out the details. As with all software, the paid versions are usually better once you learn the process.
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Thanks! This is exactly the information I was looking for. Do you have any thoughts about using an Arduino itself as a logic analyzer such as what is demonstrated here:
and provided here:
https://github.com/gillham/logic_analyzer? This is appealing because it seems like I might be able to use the arduino to analyze the signals, then program it to replicate those signals, and pop the chip out to use in my new controller. And I'd still have the Arduino to use for other projects.
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If you decide to go the other way, the manual does a pretty good job at spelling out most of the details behind the scenes. The unit seems to use a 10k nyc thermistor for the defrost sensor, so it wouldn't be super difficult to interface with. The relay and motor drivers could be found and tied into. Then you would have to write a firmware of your own.
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By this, are you talking about reprogramming the existing chip on the control board, replacing it with my own, or splicing in my own chip to the board while leaving the original in place? I'm actually waiting on delivery of a NOS control board that I picked up cheap on ebay so will soon have a spare to play around with.
Thanks much for your help. I'm finally feeling like I have a path forward.