MicroPython Forum (Archive)

8. Analog to Digital Conversion says

Please note that this input can only tolerate a maximum of 1.0 volts

while esp8266-adc-reading-analog-values-with-nodemcu says

The ESP8266 ADC pin input voltage range is 0 to 1V if you’re using the bare chip. However, most ESP8266 development boards come with an internal voltage divider, so the input range is 0 to 3.3V. So, in sumary:

-ADC Voltage range in ESP8266 development boards: 0 to 3.3V (for example: ESP8266 12-E NodeMCU Kit, WeMos D1 Mini, …)
-ADC Voltage range in ESP8266 chip: 0 to 1V (for example: ESP-07 chip, ESP-12E chip, …)

if so, is it better to mention the later one in 8. Analog to Digital Conversion?

I do not agree to the statement "most ESP8266 development boards"
It's more like "some ESP8266 development boards". Next to the listed ones for instance all Adafruit and Sparkfun boards come without voltage divider.

So the expensive versions have no voltage divider and all the cheap chinese ones do? That's interesting.. But I'd say most of the boards are chinese versions and those (afaik) have voltage dividers. At least all my NodeMCUs do.

Without the pre-built voltage divider you have more design choices when using it.
Adding the voltage divider is a valued attempt of protecting against wrong use. Especially all inputs then have the same voltage range.

P.S.: I would call all NodeMCU variants 1 model, which is made by various sources

Yeah you're probably right. They might protect themselves against claims from people using the ADC wrong and frying their chips.

PS: Absolutely, the nodeMCU is the same design from multiple manufactures. (Which is actually something nice with the esp8266 because it makes it easy to work with the same board whereas there are so many esp32 boards, you can't even design a PCB for a common esp32 board because there are so many..)

Other than finding a spec sheet. Is there a way of telling whether the board you have/are looking at has a voltage divider.
A measured impedance between the pin and ground perhaps.

I would apply 1V and see what reading came out. The voltage could be produced with series 100Ω and 390Ω resistors between Gnd and 5V.