Using ADC on ESP8266-1 to get 'system voltage'

[Fisherman48]

Hi
Moving from lua to micropython I load fw 19.1 to a handfull of old esp8266-1 1Mb and trying out my new environment using Thonny.

I want to monitor the 'system voltage' using diff power sources.
When looking at machine.ADC( ) , it accepts 0 and 1 for parameter and I get values I cant interprete.
ADC(1) looks like measuring on the absent /open ADC pin (all 16 bit ones) on the 8266-1 device - but the values from ADC(0) are no sense for me.

# dif power sources
from machine import ADC
import time
def adc(m):
    for i in range(5):
        adc = ADC(m)            # create ADC object on ADC pin
        print(adc.read_u16(), adc.read()) # the 2 available methods
        time.sleep(1)
adc(0)
adc(1)

at 3.1 V - gives 3.1V/40=0.0775
2367 38
2367 40
2431 40
2431 41
2431 41
4194176 65535
4194176 65535
4194176 65535
4194176 65535
4194176 65535
at 3.7 V - 3.7V/120=0.031
7423 120
6463 104
7359 120
7167 116
7167 116
4194176 65535
4194176 65535
4194176 65535
4194176 65535
4194176 65535

1. Any hint to understand this?
2. And more abaout python: Using help( machine) and help(machine.ADC) you see ADC is a 'class' and .ADC.read it's a function - how can I go deeper - reading the class or function argument??

Br /Stefan in the Archipelago of Stockholm

[robert-hh]

AFAIK, the ESP8266 has just one 10 bit ADC with external input, with a voltage range of 0..1V. ADC(1) is for the internal Vdd voltage. It seems that one is scaled up internally to a internal 16 bit range. The ratio you get between read.u16() and read() is always 64 or 2**6.
The value of 65535 only means that the ADC((1) overflows. for ADC(0) you have to explain, what you connected to the ADC input.

[Fisherman48]

I have 2 old? versions of the file: esp_init_data_default.bin and esp_init_data_default_v08.bin and they differ i these positions:

1 0 8
34 82 78
35 78 74
36 74 70
37 68 64
38 64 60
114 0 1

Any ideas?
BR /Stefan

[robert-hh]

Sorry, no.

[Fisherman48]

Found the c-code for the lua adc module - I'm not fluent in C but I can see they check if the 107 byte is ok depending of vdd33 or ADC pin otherwise change the byte and reboot.

https://github.com/nodemcu/nodemcu-firmware/blob/release/app/modules/adc.c

Br Stefan

[robert-hh]

You can just try and see. Using esptool.py you can as well read the esp_init_default_data.bin from flash.

[Fisherman48]

Hi Robert - to close this:
Tryed diff values on byte 107 and flashed the esp_init_default_data.bin - the byte was still intact/ same after reboot but I didnt see any change in reading voltage. So I give up digging further 'down the rabbit hole' ...
Thanks for help /BR Stefan