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Hot!VOLTAGE DIFFERENCE BETWEEN SUPPLY GND AND PCB GND

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Matías
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2021/01/23 09:42:10 (permalink)
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VOLTAGE DIFFERENCE BETWEEN SUPPLY GND AND PCB GND

HI!
I have a voltage problem between power GND and PCB GND with a DSPIC33EP. Between them there are approximately 32mV. The problem with this is that I have an analog input signal to the microcontroller, but for it to start storing data in the buffer I have to overcome that 32mV barrier.
What can I do to reduce that voltage difference to 0V?
 

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    ric
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    Re: VOLTAGE DIFFERENCE BETWEEN SUPPLY GND AND PCB GND 2021/01/23 14:59:12 (permalink)
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    Matías
    What can I do to reduce that voltage difference to 0V? 

    Improve your PCB layout.
    Plainly some of the return supply current is being observed on the ground connection between your sensor and the PIC.
    You should use a dedicated ground trace1  from the sensor ground to the PIC's AGND pin.
     
    Also, you don't mention how you know you have this exact error. You might just be observing averaged noise on the signal.

    I also post at: PicForum
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    ric
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    Re: VOLTAGE DIFFERENCE BETWEEN SUPPLY GND AND PCB GND 2021/01/23 15:01:28 (permalink)
    4 (1)
    Looking again, I don't see any ground wire on your "sensors" connector at all.
    Is that correct? Are you just relying on chassis ground for your sensors?
    I don't see any low pass filtering on the sensor inputs either.
     
     

    I also post at: PicForum
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    NEW USERS: Posting images, links and code - workaround for restrictions.
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    #3
    du00000001
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    Re: VOLTAGE DIFFERENCE BETWEEN SUPPLY GND AND PCB GND 2021/01/23 17:54:36 (permalink)
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    @Matias
     
    You can make my day by telling me that your power supply is built on a breadboard and/or wired with these fancy pluggable wires usually used in the Arduino context.
     
    What you need is a dsPIC PCB that houses the connectors for the sensors - providing power and power-GND from this PCB. Or - provided the offset is constant - you can correct the readings mathematically. But I assume your sensor's GND is -32 mV wrt the dsPIC's Vss/AVss. So the sensor readings will be a bit too low - not allowing to measure the first 32 mV at the lower end.

    PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
    #4
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