Hello!
I am trying to interface an Arduino Uno with button controls on a small electric vehicle dashboard so I can control it remotely.
The car runs on a 24V battery. I have access to pin connectors that connect the dash and the rest vehicle systems. I have been disconnecting wires one at a time and seeing what stops working to try to determine which wires carry which signals. The PCB's are covered in an opaque goop, so i'm having trouble determining which is power, ground, or signal. However I was able to determine that many are simple switches that pull up the wire 24V when activated. That is, my multi-meter reads 24V with the leads on the disconnected wire leads when the button is pressed.
I figured I could use a transistor as a switch to activate these simple controls, with the Arduino controlling the transistor gate. The transistor drain would be connected to another pin that I measured at 24V relative to the battery negative terminal, and the source would go to the pin connector. The attached picture is a rough sketch of this idea. I know this can theoretically work because shorting my selected power wire to the pins do in fact activate the controls.
The problem is I cannot get the Arduino pin outs to turn on the transistors. I think my issue is where I am connecting the Arduino ground pin to achieve common ground so that the transistor is biased correctly. I first tried connecting the Arduino ground to the negative terminal of the battery, but that didn't work. It does work if I connect Arduino ground to the transistor source, but that is silly because the 24V signal will feed back into the Arduino ground, and I don't really know what consequences that has. Where can I try to connect the Arduino ground? Why might the battery ground not be sufficient?
I appreciate any insight on my problem, or other ideas on how to hijack these signals!
Thank you!