I have a 12V power source, which powers a arduino as well as a mosfet that controls a 12v computer fan.
I wanted to measure the voltage after the mosfet in relation to my pwm signal.
I created a voltage divider on the mosftet output using 100K (+ side) and 47K resistors (- side) of which the output runs to an analog pin on the arduino.
When the output of this divider is not connected to the arduino, i get what i expect, about 3.8v when the output of the mosfet is 12v.
However, when connected to the arduino analog pin, the voltage soars as the mosfet output voltage goes down. I think I’m lucky that i haven’t fried it.
I am obviously not understanding how the ground is working through the arduino.
Can someone lend a hand?
Thanks everyone for you time!