AD7791 random values

IGOMES on Sep 15, 2021

I'm working with AD7791 and STM32, the design is based on CN0216 rev C.

Sometimes I get random values from the ADC.
Is there any mechanism to validate the data or fix this?

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JellenieR
Sep 29, 2021 in reply to IGOMES +1 suggested
Hi

Thanks for sharing I will have a look at this again. May I know if you managed to monitor the physical input voltage and see if you find similar issues?

Thanks,

Jellenie
JellenieR
Sep 30, 2021 in reply to JellenieR +1 suggested
In addition, you have mentioned above that when you disconnected the load cell, the issue is still there? May I know exactly what is the equivalent voltage of that random value? Is that the same voltage…
IGOMES Oct 19, 2021 in reply to JellenieR +1 suggested

Hi

Sorry for the delay, there are other projects! We found no problems or fluctuations in the input voltage. We are currently performing two sequential readings and comparing the results. So we can discard…

0 JellenieR

on Sep 16, 2021 1:31 AM 1 month ago
Hi,

Can you confirm what's the equivalent code for that? Is that a full scale code? Is the issue happening at specific interval or just randomly?

Can you also monitor the input and reference voltage? Is there a chance you can capture the issue while measuring the inputs mentioned?

Thanks,

Jellenie
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0 IGOMES on Sep 16, 2021 2:06 AM 1 month ago in reply to JellenieR

Hi

At this time the values do not represent full scale of AD.
It's a random problem, I'll try to capture the voltage values on the inputs.
We have already assembled other devices and the effect is the same.

Thanks
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0 JellenieR

on Sep 16, 2021 11:19 AM 1 month ago in reply to IGOMES
Hi,

May I know what is the code value? For example the 661.52 weight what is the equivalent input voltage for that? May I know also your sensor spec and sentivity? And is it also possible that you can schematic or is it really similar with the CFTL mentioned above?

I think it is weird if it really appeared randomly. So we have to understand if the issue is causing by the hardware or a software. For example if you can isolate the sensor or front end for example and just short the inputs of the ADC are you also seeing the same peak measurement?

Thanks,

Jellenie
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0 IGOMES on Sep 18, 2021 2:49 PM 1 month ago in reply to JellenieR

Hi,

I removed R43 and R44 and shorted C49.

Random values return even when we perform ADC queries at intervals greater than 500ms

In other words, slow queries

Thanks,

Ivan

PCI_SD_022021.rar
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0 JellenieR

on Sep 22, 2021 12:38 AM 1 month ago in reply to IGOMES
Hi,

Apologies. I cannot open the attached file, can you send atleast a pdf version of the schematic?

Thanks,

Jellenie
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