NRF51822 ADC float up 0.2V

RE: NRF51822 ADC float up 0.2V

Ole Bauck — Tue, 14 Jun 2016 13:51:58 GMT

The voltage at AIN after prescaling should not be more than 2.4V, so for example if you use prescaler 2/3 the maximum voltage can be 2.4V / (2/3) = 3.6V, see here.

What are the resistor values of the voltage divider? Using an external voltage divider is not that straight forward, see this blogpost.

The ADC of nRF51 should be adequate for battery measuring.

RE: NRF51822 ADC float up 0.2V

Songplus — Wed, 08 Jun 2016 03:11:25 GMT

Thanks.It is better than before,but error is beyond acceptable.The NRF5122's ADC is too bad to minitor a battery charging.

RE: NRF51822 ADC float up 0.2V

Ole Bauck — Tue, 07 Jun 2016 15:43:05 GMT

This may be because of the HFCLK is running of RC oscillator. Then the accuracy will be as bad as the accuracy of the RC oscillator. Try to sample with the crystal running. Turn it on with this code (can be done once):

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);
}