Proximity App battery service not changing

[rahul1]

I am using the nrf51422 development kit with sdk11.  I am running the proximity application for the battery life service.  I am inputting voltages ranging from 3000 millivolts to 2100 millivolts  using an external power source (not using the USB).  Regardless of what value I input I am still receiving a value of 0x64 through the nrf connect app.  I have eliminated the diode voltage drop and still I am receiving the same value.  I waited the default measurement period of 120 seconds and still the percentage did not change.  For example I am using 2300 mililivolts.  I am expecting a value close to 3 but I am still receiving 0x64.  What could the problem be?

[Einar Thorsrud]

Hi,

You should get a sensible number provided that you wait 180 seconds. In that case the battery level is calculated by battery_level_in_percent(), and should be just a few percent. How do you power the board? I assume you have verified the supply voltage? What ADC reading do you get if you put a breakpoint in the adc_event_handler and inspect the batt_lvl_in_milli_volts value?

[rahul1]

I am powering the board using an external battery connected to the vdd pin. I am a bit confused of how the conversion works. Can the board be both powered by the battery and calculate it’s percentage value if it is connected to the vdd pin? 

[Einar Thorsrud]

Hi,

Yes, the ADC has a dedicated input connected to VDD. However, this is in fact not a very good way of measuring the battery voltage, as the voltage will typically drop when the ADC is enabled, drawing a lot of current. The voltage drop depends on the current charge of the battery, the internal resistance of the battery and the current consumption of the board at the time of sampling.