Voltage divider and NodeMCU inputs Some sensors give as output a voltage between 0 and 5V. The analog inputs of the NodeMCU require voltages between 0 and 3.3V. I plan to make a voltage divider with two resistors like in this link for compatibility. 

To provide the desired voltage the quotient of the values of the resistances is fixed (approx. 1/2 for this case). However, the absolute values of the resistances are not.

Q: How to choose those absolute values? Which are the criteria and why?

I have a good background in electromagnetism but I know very few about electronic Engineering.

I think that low values must work, e.g. 1Ω and 2Ω (and surely greater values). But I am unsure of VERY high resistance values because I suspect that there should be some current intensity requirements. 

Thank you.
As @Majenko commented, the A0 input has a fixed voltage divider (see NodeMCU Schematics) that connects the A0 input to a 220kOhm resistor, then to the ADC pin of the ESP8266, then to ground via a 100kOhm resistor. 



This effectively fixes the resistor values that can be used to scale the input of the NodeMCU. For a 0-5.0V input range (with sufficiently low impedance) you need to scale the ADC pin from 0-1.0V by adding a ~180kOhm resistor between the 5V output and the A0 input of the NodeMCU, creating a 400kOhm-> ADC -> 100kOhm divider like this:







simulate this circuit &ndash; Schematic created using CircuitLab