Got a puzzling mystery for someone with better understanding of electronics than me. I am trying to read an automotive mass air flow meter with arduino nano. I have it setup as follows.
Arduino + and - come from the car ECU’s regulated 5v output.
The MAF meter hot film needs 12v and the device outputs a 0-5v signal to indicate mass flow.
The 12v to the MAF hot film is supplied via the battery + and -.
The - of the MAF output is connected to gnd on arduino and the + of the output is connected to analogue input 4.
Here is the problem. When the connection from the ECU is unplugged and the arduino has no connection to GND or 5v, the voltage across the MAF sensor output is correct about 0.2v with no flow. When I plug the arduino in I measure about 2.7v across the MAF output with no flow. Im not sure what is causing this. Any ideas? I would imagine its no coincident that its shifted by half of 5v.