Post links and attach files for documentation here, also chat about these docs freely

User avatar
By sibianul
#70474 Hello everyone,

I just received this module, and this weekend I wanted to make a small program to monitor the outside temperature and humidity, but also plug it in at 5v from a small 250mA solar panel, as a test to see if this can work continuously with only power from the solar panel (to recharge the battery).

I want to monitor the battery voltage also, and I see that next to the A0 pin on the board there are 2 resistors, is that a voltage divider, is it already connected to the ESP analog input pin ?

Anyone that can provide some advice's, or documentation for this board please reply to this thread.

Thank you

UPDATE. 120 views and nobody knows ?

ESP-WROOM-02 with 18650 battery.jpg
You do not have the required permissions to view the files attached to this post.
User avatar
By sibianul
#70659 Can you tell me what resistors do you use to reduce the voltage from 4.2v to 1v ? I have tried many variants but I didn't had any success :( R1 - 15k ... R2 - 4k7 is reporting a vlue of ~200 on the pin, also measured it and it's about 0.22v with a 3.9v batery.

I than tried with just one resistor, still no luck.
User avatar
By schufti
#70660 as you allready wrote, there are two resistors close to A0.
You have the board, you see the traces.
If you have a meter, just check if there is resistance between A0 pin of the board and A0 pin of the module.

Your results with external resistors make it very clear that there allready is an divider network on board.
A little bit of googling even shows some results: ... fi-module/

To charge/feed via solar panel you should connect the panel to "Vcc" (that you have to find on the pcb) to avoid powering/damaging cp2102 from solar panel.