Electric gauge hums with PWM

I am reading a thermistor with my Arduino, interpreting the signal, and converting it to a duty cycle for PWM to manipulate a dial gauge in an interment cluster. I’m using the temperature input signal to control the electric cooling fan as well as an “idiot” light on the dash. I don’t think it’s a real problem but want to know if I can do something about it. The car is loud enough so I can’t hear the hum coming from the gauge. In the bench testing phase I could definitely hear it. When the duty cycle is 100% the noise goes away. So, I know it’s the PWM doing it. Is this hard on the electric gauge?

What type of instrument gauge are you using? There is a XOD library for the Switec x27 589:

@fusionfanatic made a great video on how to use it:

That’s interesting. I’ll look into it this weekend. I wasn’t sure if i could put a filter on the PWM signal to reduce or eliminate the hum.

Hi, thanks for the mention Matt, I have left this project somewhat neglected for the last 18 months only to start looking at it again last week! takes a minute to get back into whats going on. Last element I was working on is smoothing the input to prevent the stepper “hunting” with small fluctuations in the input signal.

@fusionfanatic - for smoothing you could try a running mean or running median:

Thanks Matt, I will try that when I get back into it!

I haven’t realized this problem yet, I thought it has always been there.

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