Max ADC value not equal to VDD for NTC mesure

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stefkpl
Posts: 3
Joined: Thu May 23, 2019 11:07 am

Max ADC value not equal to VDD for NTC mesure

Postby stefkpl » Thu May 23, 2019 11:36 am

Hi guys,
I would like to mesure temperature with a NTC sensor.
First, I had wrong mesure, less than 3 °C.
And after 4 hours, I have try to mesure voltage of pin in.
The probleme is, on pin13 ADC2_4 (and the others), the maximun value is 3.2V and not VDD :(
How can I solve this, because I can't mesuse correctly my NTC if VDD change.
Value of MAX_CONVERSION (4095) must be equal to VDD.
So, if VDD value down, the calcul of the equation to know R_NTC not change because equation is proportionnal.
Thank's
Stéf

-Rudy-
Posts: 18
Joined: Sun Feb 05, 2017 1:08 am

Re: Max ADC value not equal to VDD for NTC mesure

Postby -Rudy- » Sun May 26, 2019 11:35 pm

I have not done much with the A/D on the ESP32 but from what I have it seems to be a big problem. Lots of noise, inconsistency and mo useful reference. If the reference was Vcc then ratiometric measurements would track if Vcc was used for the measured device reference. If the actual reference for the A/D was brought out, that would be workable, but I have not found that ability.

The best that I can think of is have Vcc as the sensor reference. Use an A/D input to measure the supply voltage and do a compensation.

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