Unaccurate battery level measurment on Beacon device

RE: Unaccurate battery level measurment on Beacon device

Stefan Birnir Sverrisson — Tue, 22 Jul 2014 13:41:46 GMT

I apologize again for a very late response. I was on vacation.

Do you have an answer to your question yet? 60mV measurement error is very high. For 10 bit measurement it is around 17 bit error.

My question is: when are you measuring the battery voltage? If you measure it during a radio event, you will measure lower voltage then when measuring when the chip is idle and not consuming a lot of current. How much voltage drop is during the radio event (or whenever the chip consumes the most current) really depends on the internal resistance of your battery, which is very different for different battery manufacturers. Ideally you should measure the battery voltage at the moment the chip is consuming the most current.

RE: Unaccurate battery level measurment on Beacon device

Sébastien Despont — Thu, 26 Jun 2014 14:09:34 GMT

Hi Stefan, Thank you for your support. I agree with the fact that enable 16MHz for the battery measurement is nonsense in my case, but I would my code be closest to the Nordic reference code found in the GitHub repository before asking for help. At this time, I removed the 16MHz enabling code for the battery measurement. I can ensure you that my code is really minimal and nothing is enabling before the end of the battery check. I was doing the battery measurement in debug mode (with the segger connected to the computer) which is bad. The value is close to the reality now: -60mV But, all the battery measurements done with the development kit are really accurate. Can you confirm that a difference of -60mV is acceptable for ADC measurements using a button battery CR1632? Best regards

RE: Unaccurate battery level measurment on Beacon device

Stefan Birnir Sverrisson — Wed, 25 Jun 2014 04:50:44 GMT

Hi Sebastien

I am unhappy about that I did not see your message before. Sorry for the late response.

What is actually the current consumption of your beacon device by the time you are sampling. If it is high, the measured voltage is lower than the battery voltage that you measure with your voltage meter. This is because of the internal resistance of the battery, which will create a lower battery output voltage on high current drain. The internal resistance of the battery greatly varies between battery manufacturers and battery types.

To check if the high current consumption is creating that much difference in the battery reading, try to not request the high frequency clock. Enabling the high frequency clock will create most of the current consumption for the ADC sampling, so by not enabling the high frequency clock, the current consumption should be much lower and you should see some difference in your ADC readings.

However, measuring the battery voltage when the device consumes the most current is perhaps the preferred method for battery level measuring.

RE: Unaccurate battery level measurment on Beacon device

Dan Danknick — Wed, 25 Jun 2014 01:44:27 GMT

Are you running on the Eval Board or your own HW? If your own, you certainly want to set DIODE_FWD_VOLT_DROP_MILLIVOLTS to 0.

Dan

RE: Unaccurate battery level measurment on Beacon device

Sébastien Despont — Tue, 24 Jun 2014 15:09:07 GMT

After 4 weeks, still no help for my problem. Is there someone to help me to figure this out?