RE: ADC measurement unstable relative to VDD reference?

kurtovic — Fri, 03 May 2024 16:56:42 GMT

Yes those are the raw samples from the SAADC, 10-bit values ranging from 0-1023.

The setup is a custom board which takes a CR2 3V battery, and the AIN4 input interfaces to the board via a PCI-E style connector. The board will not power up until the PCI-E connection is made. By "reseating" I mean essentially causing the unit to power cycle/cold boot, either:
1. Remove battery, then put battery back in; or
2. Remove AIN4 PCI-E input, then put AIN4 PCI-E input back in

I contacted the hardware designer, and was informed that this may be an issue with the board and/or AIN4 input itself. See image below. The AIN4 input consists of several resistors which may have been unnoticeably damaged in some way and become extremely sensitive to environment. (For reference ~540-550 is the expected value for AIN4)

I will continue monitoring and try isolating the issue to rule out hardware problems before pursuing further support and providing a pseudo-code sample. I've swapped the AIN4 PCI-E input between the above unit and an acceptable unit to see if it can be reproduced over the weekend.

Thank you

RE: ADC measurement unstable relative to VDD reference?

Jørgen Holmefjord — Thu, 02 May 2024 15:01:10 GMT

Hi,

Are the plots based on raw samples from the SAADC? Can you provide the samples, both with and without oversampling enabled?

Can you post your code?

I'm not sure exactly what you mean by "reseating the battery and/or AIN4 input". Can you post a picture of your setup and describe the exact process?

Best regards,
Jørgen