MicroPython Forum (Archive)

Hi All,
New here and not seeing any way to post code, apologies if I am getting up your noses already!

Anyway, I have a Wemos D32 ready to deploy, deep sleeps for most of the time but should check IO35 on wake-up to alarm in case of low battery. Seems that any time I read Vbatt I get full scale 4095 on the ADC? No errors, just 4095 irrespective of battery volts?

on the REPL I get...
>>> import machine
>>> adc = machine.ADC(machine.Pin(35))
>>> adc.read()
4095

Same result any time I call the adc.read() function in my code?

Is the ADC broken in the esp32 port at the moment or am I possibly messing with a fake board with no voltage divider on IO35?

Anybody else come across this?

Many thanks in advance
Garry

The basic voltage range of the ADC is 0-1V. you can change that with an attenuator setting to about 1-3.2V if you need a wider range, you have to add your own voltage divider. The documentation about that for ESP32 is pretty sparse.
Setting the attenuator is something like:

Many thanks @Roberthh, that works well. I must crack out the multi-meter now and calibrate...

Garry

Roberthh wrote: ↑

Thu Jan 03, 2019 7:27 pm

The documentation about that for ESP32 is pretty sparse.

Tangentially...Note that I've made a start on the ESP32 documentation. You can view it or contribute via a pull request.

I've just created an issue: Need to improve ADC documentation. If someone could submit a PR that'd be great! Otherwise I'll get to it when I can.

It's not perfect but the ESP32 ADC QuickRef has improved. Well, it exists now.

We also need an ESP32 reference - then we can go into a little more detail about the ADC details. However the QuickRef and least touches on some of these points though it is meant to be terse.