nrf52832 adc wrong value

[Berker]

Hi,

I try to read analog voltage over P28. Digital value(result variable in the code) always 238 as decimal. 

What is the missed thing in the code? 

Voltages supplied with power supply(as 0.5V,1V,2V)  

  volatile int16_t result = 0;
  volatile float precise_result = 0;
  
   //HFCLK
  NRF_CLOCK->TASKS_HFCLKSTART = 1;
  while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
  NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
  
  NRF_SAADC->CH[4].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_6    << SAADC_CH_CONFIG_GAIN_Pos) |
                            (SAADC_CH_CONFIG_MODE_SE         << SAADC_CH_CONFIG_MODE_Pos) |
                            (SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos) |
                            (SAADC_CH_CONFIG_RESN_Bypass     << SAADC_CH_CONFIG_RESN_Pos) |
                            (SAADC_CH_CONFIG_RESP_Bypass     << SAADC_CH_CONFIG_RESP_Pos) |
                            (SAADC_CH_CONFIG_TACQ_3us        << SAADC_CH_CONFIG_TACQ_Pos);
                            
  
  NRF_SAADC->CH[4].PSELP = SAADC_CH_PSELP_PSELP_VDD << SAADC_CH_PSELP_PSELP_Pos;
  NRF_SAADC->CH[4].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
  
  NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_8bit << SAADC_RESOLUTION_VAL_Pos;
  
  NRF_SAADC->RESULT.MAXCNT = 1;
  NRF_SAADC->RESULT.PTR = (uint32_t)&result;
  
  NRF_SAADC->SAMPLERATE = SAADC_SAMPLERATE_MODE_Task << SAADC_SAMPLERATE_MODE_Pos;
  NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;
  
  NRF_SAADC->TASKS_START = 1;
  while (NRF_SAADC->EVENTS_STARTED == 0);
  NRF_SAADC->EVENTS_STARTED = 0;
  
  NRF_SAADC->TASKS_SAMPLE = 1;
  while (NRF_SAADC->EVENTS_END == 0);
  NRF_SAADC->EVENTS_END = 0;
  
  NRF_SAADC->TASKS_STOP = 1;
  while (NRF_SAADC->EVENTS_STOPPED == 0);
  NRF_SAADC->EVENTS_STOPPED = 0;
  
  result;
  precise_result = (float)result / 4551.1f;
  precise_result; 
  
  while(1) //breakpoint here
  
  

Thanks

[Sunil vignesh]

Hi Berker,

I also need to read the battery value. but with out adc is it possible to read the battery level with internal registers. If adc is used means can you give any schematic related to ADC connection. It will be helpful for my project.  

[Berker]

Hi Sunil,

Look at this link: 

https://devzone.nordicsemi.com/b/blog/posts/measuring-lithium-battery-voltage-with-nrf52

You can do simple voltage divider and add one capacitor. I think, reading battery can done with voltage similar above example.  

[Sunil vignesh]

Hi Berger,

I will check the link sir. but by using this. How to set the voltage reference sir. we need to put one voltage regulator to give voltage reference value as constant one right?. or we can use SAADC to measure (0-VDD), without any voltage divider..!.

[Berker]

Hi,

You can use internal reference and gain(1/6) to measure between 0 to 3.6V. 

For example

ADC range = 0.6V/(1/6) = 3.6V

ADC range = 0.6V/(1/2) = 1.2V, you change it as desired

You may not use external regulator or reference,there is internal one. It is possible to adjust gain 1/2,1/3,1/4,1/5,1/6,1,2,4 using CONFIG register directly or SDK convenient function.