I have a project that I am working on. I want to build a small dashboard that displays several readings from my engine. This is in a classic Mustang, so there is no OBDII or such to use.
What I am monitoring is RPM (via this little module here), vacuum via a 0-5V analog sensor, and air/fuel via a PLX module that will either provide 0-5V analog or, if I can figure it out, a serial connection. I have that part figured out. I have yet to try to get the BLE to send it, but that’s not the issue I bring today.
I want to monitor the cooling fan. All I want to know is if it is on or off. I have a relay controlled via a thermocoupler that goes to ground at 195 degrees, triggering the 12V relay to turn the fan on. I am trying to figure out how to use that ground to trigger a digital input. I could run it off the 12V+ going to the fan, but using the ground seems safer (no level shifting)
I know this should be probably the easiest of the 4 to do, but I am having a mental block. Any suggestions in either direction?