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Feather ADC comparison including 2.6V limited ESP32-S2
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Feather ADC comparison including 2.6V limited ESP32-S2

by kevinjwalters on Tue Jan 12, 2021 1:51 pm

Here's a graphical comparison of the ADCs on four Feather boards including the FeatherS2 which uses the ESP32-S2 which appears to have an unfortunate limitation with its ADC voltage. The Feather M0 Bluefruit DAC is providing the voltage into a 0.1uF capacitor. The boards are:

  • FeatherS2 from unexpected maker - red
  • Feather nRF52840 Express - purple
  • Feather M0 Bluefruit - light brown
  • Feather M4 Express - sky blue

adc-analaysis-run1-20210112-g1.png
Comparison of ADC on four Feather boards
adc-analaysis-run1-20210112-g1.png (325.89 KiB) Viewed 77 times


I discovered this when testing an Enviro+ FeatherWing with the FeatherS2 as the ADC limitation will cause bogus readings sometimes from the gas sensors. It's been discussed before in these tickets:


kevinjwalters
 
Posts: 836
Joined: Sun Oct 01, 2017 3:15 pm

Re: Feather ADC comparison including 2.6V limited ESP32-S2

by kevinjwalters on Wed Jan 13, 2021 3:00 pm

I had another play with the data, here's the difference between the DAC output and the four boards. It's not really a true error as there's no calibrated reference voltage measurement just the value set on the SAMD21 DAC. It's still interesting to look at the distribution and patterns. I've split out the samples too, the program on the Feather boards produced measurements based on 1, 8 and 50 samples averaged, if you look closely these are now rendered with different shapes.

adc-analaysis-run1-v2-g2g3.png
Comparison of ADC on four Feather boards - difference between ADC values and DAC output
adc-analaysis-run1-v2-g2g3.png (504.44 KiB) Viewed 51 times


Ignore the 1.25 on the upper legend, that legend was supposed to be suppressed...

kevinjwalters
 
Posts: 836
Joined: Sun Oct 01, 2017 3:15 pm

Please be positive and constructive with your questions and comments.