ADC receiving 1024

[beckmx]

Make sure you read and understand http://nodemcu.readthedocs.io/en/dev/en/support/.
Use one of the two templates below and DELETE THE REST.

8<------------------------ BUG REPORT -----------------------------------------

Expected behavior

Get readings of a voltage devider with GND and 3.3

Actual behavior

ADC reading shows only 1024

Test code

Provide a Minimal, Complete, and Verifiable example which will reproduce the problem.

if adc.force_init_mode(adc.INIT_ADC)
then
  node.restart()
  return -- don't bother continuing, the restart is scheduled
end
print(adc.read(0))

NodeMCU version

Which branch are you on? If you know the Git revision then add it here as well.
branch: master
commit: 68c425c
SSL: false
modules: adc,bit,cron,file,gpio,mdns,net,node,pwm,sjson,spi,tmr,uart,wifi

Hardware

Describe which ESP8266 device you use and document any special hardware setup
required to reproduce the problem.
ESP12E single module

[KT819GM]

As your example is working with at least latest master branch (as of 2019 08 12), you should consider checking hardware part.

[ildar]

BTW note that max voltage shown by ADC is 1.0 V

[jmd13391]

IMO, this is not a firmware issue nor is it an application developer issue...

• Many / Most ESP8266 development boards come equipped with an on-board 1% tolerance voltage divider connected between the ESP8266 module and the board's ADC input pin (A0). This built-in voltage divider increases the 1.0 volt max of the ESP8266 module's ADC to 3.3 volts... i.e. an adc.read(0) with 3.3 volts connected to the board's pin A0 will return a value of 1023.

• An adc.read(0) value of 1024 indicates a voltage out-of-range condition (i.e. > 3.3v). Remember: there is a +/-1% tolerance with the built-in dev board A0 pin voltage divider (if that's what you're using).

• Use of the ESP8266's built-in ADC should be limited to applications that do not require accurate or stable readings... this is because the ESP8266's ADC is neither (IMO, it sucks). This accuracy / stability issue is the result of an internal design flaw in the ESP8266 chip (it is most noticeable during times of WiFi activity). The accuracy / stability issue can be somewhat mitigated with exponential moving window and medians algorithms but it cannot be complete eliminated. Consider using an external ADC like the ADS1115 or ADS1015.

[beckmx]

Actually, after a carefull read, I realized that the nodemcu and wemos board uses internal voltage dividers (resistors), and I created my own module without including those, so, my mistake, after creating my own voltage divider I could see the values