I have arduino uno that i use to measure the volt of li-ion 3.7V using Analog input pin but when i connect li-ion battery with protection circuit the the voltage does not change, but remains constant around 3.2V. so i can not determine how the real volt of battery how can i solve that???
Welcome! post your code and a simple schematic showing what you did. How do you know that 3.2V is wrong? I assume the UNO is running on 5V.
I just connect the positive terminal protection circuit (bms) with 10k resistor then connect with A0 pin when i convert the value along to volt it remains about 3.2.
The problem is not in code or arduino uno i want to know if there way to read real value of battery that connects with(bms).
I am confused as to what you are doing. Post an annotated schematic showing exactly how this is wired.
I do not recognize the Arduino in your picture. If it is a 3.2V device you may be forward biasing the protection diode on A0, thereby reading the Vcc voltage + ESD protection diode forward voltage. You would get a lot better help if this were not such a secret project and the needed details were given such as manufacturer, links to technical information etc.
Either your BMS is no good or your battery is almost dead.
if i connect the battery with protection circuit What value of voltage battery
should be obtained?
If the battery measures 3.7V then you should see 3.7V or very very close to that voltage.
Try connecting a 1K resistor between the BMS + output and BMS ground and then measure the voltage