Esp2866 adc

[be80be]

The ADC on the esp2866 12E is only able to read 0 to 1 volt. So i have a divider that scales the 3.3 volt to 1 volt on the input but my reading are way off
Im getting 180 with adc.read and it's .227 on the pin and .505 at the tmp36 so if I change to volts the 180 it doesn't scale to .505 volts. That the tmp36 is showing
I'm .075 off of a real reading.

 

[ericgibbs]

hi Burt,
What is the input impedance of the esp adc input.?
Also what are your resistive divider values.?
E

 

[be80be]

Hi eric I'll see if I can find that the board I was using for testing is a nodemcu it has a 220k and 100k divider I don't think the datasheet goes into detail on the ADC input pin.
But I did a lot more reading last night and it may be the firmware that's the problem. Or the program I'm using to test with.

 

[ericgibbs]

hi burt,
For comparison a PIC's ADC input, expects the source resistance to be less than 5k or 10k impedance.
Higher than that will cause apparent lower adc readings.
Depending upon the sampling rate, for slower rates its possible to add a 10nF cap from the adc input pin to 0v.

I would say the 200k/100k divider is far to high a resistance and its that which is a problem

E

 

[be80be]

Well I had a chance to mess with this tonight and the ADC on the esp2866 is not very good I get 240 and it should be 232 And seeing the nodemcu is made with a 220k to 100k divider I hooked up a module with a 2k to 1k and set it dead on 1 volt and it shows the same reading as the nodemcu. got figure this out looks like a lot of people are having the same problem.