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PWM signal is shaky at low voltage levels + voltage offset

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  • PWM signal is shaky at low voltage levels + voltage offset

    I am trying to control another device using one of my PWM pins. It's a linear voltage ramp starting at 0V and ending at 3.3V. The Maximum voltage must be reached after 30 seconds. I recorded the output (PWM) signal using a professional measurement system. In the first 5 seconds namely between 0-1.2V the PWM signal is not clean. I get what seems to be random peaks. The device I am trying to control reacts to these peaks of course. That's why I would like to get rid of them.

    If I start my Voltage ramp at around 1.2V then I get a clean PWM signal (ramp with no random peaks). The Display seems to be struggling with anything below 1.2 Volts. Is there a logical explanation for that? If yes, how can I get rid of these peaks?

    Another problem is that I am always measuring an offset of 0.2V. Even when I am not sending any PWM signal, the PWM pin has a constant voltage of 0.2V. Is this normal?

    Thank you very much in advance!


  • #2
    I was wondering about your filter circuit until I saw the 0.2v offset.

    I think you have a gnd issue between the display the device you are trying to control. This will be the cause of the offset, and almost certainly the peaks.
    Mark

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