Yet another ADC question

RE: Yet another ADC question

Ole Bauck — Tue, 26 Jul 2016 09:10:24 GMT

Since it looks like this is connected to the RTC I have a few question about that:

With prescaler equal to 7 the RTC will overflow after 4096 seconds. Do you do anything in your code when the RTC overflows or when the RTC counter is equal to compare value CC[1]?

RE: Yet another ADC question

Valer_I — Wed, 20 Jul 2016 11:12:41 GMT

Yes, and it really defferent, sometimes) I measured voltage by the multimeter directly on battery.

RE: Yet another ADC question

Ole Bauck — Wed, 20 Jul 2016 10:34:55 GMT

Ok, then I understand the your setup. Have you measured the battery with an external tool (like multimeter) to see if the voltage is as the ADC measures or not?

RE: Yet another ADC question

Valer_I — Wed, 20 Jul 2016 09:02:24 GMT

Ok thanks, I'll try HFCLK
You are right, it is battery discharge graph. I use nrf51822 as test equipment to measure battery discharge with specified load. (Battery is not connected to board except ADC IN pin).

RE: Yet another ADC question

Ole Bauck — Wed, 20 Jul 2016 08:55:30 GMT

Ok, then that is not the case.

Could you try to not put the device to sleep (not call sd_app_evt_wait()) and see if the result is the same. You can also try to keep the HFCLK on all the time with:

uint32_t p_is_running = 0;
sd_clock_hfclk_request();
while(! p_is_running) {                             //wait for the hfclk to be available
    sd_clock_hfclk_is_running((&p_is_running));
}

And see if the result is still the same.

Just wondering: You say that you use line adaptor, but the graph looks very much like the discharge curve of a battery (if you don't look at the erroneous measurements). You are sure that the graph is not when measuring battery?

RE: Yet another ADC question

Valer_I — Wed, 20 Jul 2016 08:44:46 GMT

No, we developed our own device. It is battery powered, but for the test I used wire connection to AC-DC adaptor + 3.3V LDO regulator. So I continue investigation)

RE: Yet another ADC question

Ole Bauck — Wed, 20 Jul 2016 08:41:04 GMT

Sorry for confusing you, I meant the diode on the nRF51 DK. On the nRF51 DK there is a diode between the supplies (pin, battery or 3.3V regulator) and the Vdd, see the schematics in the nRF51 DK Hardware Files. Are you using nRF51 DK or other hardware?

RE: Yet another ADC question

Valer_I — Wed, 20 Jul 2016 07:30:03 GMT

Hi, the logics is simple, at least I didn't find anything current consuming. I configured ADC for Vbg reference and 1/3 prescalling. So it should measure up to 3.6v input voltage. What link with protection diode drop? I will measure VDD to check, but only thing I could imagine is if it heating much and Vbg zenner drifts.

RE: Yet another ADC question

Ole Bauck — Tue, 19 Jul 2016 11:34:02 GMT

Do you do anything in the code when the counter reaches CC[1]? Possible reason for the wrong measurements could be that system draws more current and the diode between the supply and Vdd has higher voltage drop. Have you measured Vdd to see if this is also constant?