I am using the Waveshare High-Precision AD/DA Board with my Pi to read an analogue 0-5v signal.

I am using a 5V reference voltage, but I can't seem to read full scale.

  • Applying 0V reads out -344 bits (~0V)
  • Applying 3.3V reads out 5559000 bits (~3.3V)
  • Applying 5V reads out 6698000 bits (~4V)

Can anybody advise on how I can read full scale? I'm using PiPyADC.


  • What does reads out x bits mean? You haven't given enough information to provide an answer.
    – joan
    Mar 18, 2019 at 11:34
  • Sorry, PiPyADC is a python script and reads the bits out (which are generated by the ADC) and converts to a voltage reading. It seems to max out at approximately 6698000 bits, which is equal to a voltage of 4V. My issue is it's meant to go up to 5V but I don't seem to be achieving this span
    – Tom
    Mar 18, 2019 at 11:53
  • So your resolution is ~0.6 microvolt per bit? Is this value documented somewhere? How precisely do you measure the voltage that you apply? Mar 18, 2019 at 12:58

1 Answer 1


I have posted a new question about a problem close to yours.

In my case, I didn't have any problems of full scale output with PiPyADC. The example.py given needs to be modified because it's a test case of the Waveshare card (potentiometer and Light sensor on firts ADC channels, ....) but when you have made these changes, everything works well to me.

I think you have followed all the jumpers and wiring procedure but in case, you can verify that you don't have the jumper of Vref on 3,3V, ... as described in the PDF.

You have some configuration informations that you can also try to change in ADS1256_default_config.py

To make a test, you can also try to use directly the functions defined in the pipyadc.py file as : read_continue


I used them into my own Python program directly and it works well, and the digital output reaches 5V...

If this can help you...

Good luck, best regards

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