I have a project with ESP8266. It will run with Li-Ion battery, solar panel to charge and a buck-boost 3.3V regulator.
I want to monitor the Li-Ion battery using ESP8266. It has an ADC with max voltage of 1.0V. So I'm thinking to use a voltage divider (see schematic). I set high value resistors to minimize power consumption.
Will that circuit work? Is there any sideeffect using so high values?
simulate this circuit – Schematic created using CircuitLab
Best Answer
Here's how to figure it out.
In the datasheet for your ADC, there should be two important specifications:
Maximum source impedance.
This is the highest resistance you can feed the ADC from. In your circuit, the source impedance is R1 and R2 in parallel, or about 80K. If the max permitted source impedance is less than 80K, you need to re-design.
Minimum input impedance.
This is the input circuit of the ADC, modelled as a resistance connected in parallel with R2. Let's say it is 10M. (In practice most ADCs will do better than the specification, but you can't rely on that). Calculate the ADC voltage for the most critical battery voltages, with and without thet input impedance in parallel with R2. It will be different ... but how different, and is that difference large enough to upset your calculations? If so, you need to re-design.