ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

vseven
Posts: 21
Joined: Wed Aug 30, 2017 3:22 am

Re: ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

Postby vseven » Wed Mar 14, 2018 2:17 pm

hgptamn wrote:Getting an official answer from Espressif, they do plan on fixing the factory calibration in the near future
I'm assuming since you get a reply in January and you are posting in February that the fix date is June 1, 2018? Thats a long time to wait for something that should have worked on day one.
ESP_Dazz wrote:Hi everyone, the ADC calibration issue has actually been addressed in the esp-idf.
Can you comment if there will there be a revision number or indication printed on the chips that have this new factory calibration so if/when we order we can be assured to get the correct part? Right now it is almost impossible to mass produce anything with a ESP32 chip using the analog inputs. Manually calibrating each chip is not a viable option other then for testing or one-off situations.

ESP_Dazz
Posts: 50
Joined: Fri Jun 02, 2017 6:50 am

Re: ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

Postby ESP_Dazz » Mon Mar 19, 2018 3:46 am

vseven wrote:Can you comment if there will there be a revision number or indication printed on the chips that have this new factory calibration
Please contact the sales team at sales@espressif.com, they can help with this question

muthukumar
Posts: 1
Joined: Thu Apr 12, 2018 5:02 am

Re: ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

Postby muthukumar » Thu Apr 12, 2018 5:31 am

Hi,

Esp32's recent ADC non-linear fix in esp-idf works well only for the inputs in this region 0.13Vref to 0.93Vref approximately. For lower (<0.13Vref) and higher region(>0.93Vref), non-linearity still exist. We try to fix this by adding a offset value, but for direct battery operated application(unregulated supply), as the supply voltage changes, the offset also needs a further correction.

so my question is will the express-if fix this non-linearity in hardware instead of software in near future (in few months)? For our application, this issue gives worst results. we are now forced to drop esp32 and look for other low cost alternatives.
For many IoT applications, ADC is a must needed one. So please fix this at the earliest.

if hardware fix is in near future(< 2months) please intimate me, will wait for it ?

Jezza68
Posts: 1
Joined: Wed Jun 13, 2018 1:51 pm

Re: ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

Postby Jezza68 » Wed Jun 13, 2018 2:23 pm

As many on this thread, I have experienced the problematic Non-Linearity of the ESP32 ADCs. Because of this, using ESP-32 for production still appears out of the question. A shame really, as the prospect of being able to use a chip with a decent number of Analog inputs was great.

Like many, I have found that:
a. Analog readings are non linear in nature (channels 0, 3 and 6),
b. Readings are unstable and unpredictable (the same setup/code/circuit produces different readings over time),
c. Readings are noisy (but this is by far not the worst issue as this can be dealt with by using capacitors and or statistical sampling, etc.)
d. The role played by internal voltage reference (VREF) is still not totally known (to me at the very least).

So my question to this crew:

1. Has the ADC non linear issue been fixed as previously indicated by ESPRESSIF?
If this is the case, can someone with knowledge point me in the right direction (if the fix is code), or can someone let me know how to source a chip with the fix? (version number, etc..) if the chip has been produced yet.

2. Arduino is about to release the Arduino MKR 1010 with ESP-32.
Does anyone know if this board will address the issue of ADC non linearity?

Thanks a lot for the help provided.

plajjd
Posts: 17
Joined: Thu Jul 05, 2018 11:47 pm

Re: ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

Postby plajjd » Thu Aug 02, 2018 4:04 pm

I also am considering using the ESP32 for a production product and am very concerned about the ADC calibration and non-linearity issue.

Are there any updates on the following?

1. How can I be sure that the ESP32-WROOM-32 modules I purchase have been factory calibrated?

2. What exactly are the voltage input ranges that may be significantly non-linear?

3. Can I provide a high quality external voltage reference to solve the calibration & nonlinearity issues?

Thank you!

Archibald
Posts: 106
Joined: Mon Mar 05, 2018 12:44 am

Re: ESP32 ADC Non-linear Issues - How do I fix / change Attenuation or width?

Postby Archibald » Fri Aug 03, 2018 3:35 am

Non-linearity is bad with 11dB attenuation and input voltages greater than about 2.6V, as shown by the graph in the original post of this thread. Factory "two point" calibration will not remove that non-linearity. From my measurements, graphs with 6dB and 0dB attenuation appear to have good linearity.

As far as I am aware, you cannot provide an external reference voltage.

In my view 'noise' causing variation of digital values is more concerning than non-linearity, especially if measuring voltages that change fairly quickly.

For production I would use a separate ADC integrated circuit.

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