Measure battery voltage too high and how to use mutil ADC

[Alice]

Hi,

I'm using nRF52832 with S140 v7.2.0 base on nRF5_SDK_17.1.0. I use PCA10100 development kit and set VDDH/5 as input and use internal reference (0.6 V) to do the battery measure. I found the battery voltage measured is a bit high(3.3v) than the actural voltage(3.0v) . The ADC configuration as bellow:

void saadc_init(void)
{
    ret_code_t err_code;

		nrf_saadc_channel_config_t channel_config_NTC = {
    .resistor_p = NRF_SAADC_RESISTOR_DISABLED,      
    .resistor_n = NRF_SAADC_RESISTOR_DISABLED,      
    .gain       = NRF_SAADC_GAIN1_6,                
    .reference  = NRF_SAADC_REFERENCE_VDD4,     
    .acq_time   = NRF_SAADC_ACQTIME_10US,           
    .mode       = NRF_SAADC_MODE_SINGLE_ENDED,      
    .burst      = NRF_SAADC_BURST_DISABLED,         
    .pin_p      = NRF_SAADC_INPUT_AIN5,       
    .pin_n      = NRF_SAADC_INPUT_DISABLED          
		};
		
		nrfx_saadc_config_t    saadc_NTC_config = {
      .resolution = NRF_SAADC_RESOLUTION_12BIT       ///< Resolution configuration.
		};		
		
    err_code = nrf_drv_saadc_init(&saadc_NTC_config, saadc_NTC_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(1, &channel_config_NTC);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}

I use the ADC result to caculate valtage such as: valtage=(ADC_VALUE*6*1200mv)/1024*5, 6 means NRF_SAADC_GAIN1_6, 1200mv means NRF_SAADC_REFERENCE_VDD4, 1024 means NRF_SAADC_RESOLUTION_10BIT and 5 means VDDH/5 as input.

Is there any problem with my code?

Besides, I want to use 4 ADC in total. But when I use the same way to configure another ADC as follow, it returns 0x11 error.

    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

Could you help me have a look? Thanks a lot.

[Alice]

Hi Jared,

Yes, I did't modify anything in the code and it is the same code as when I plugged the DK to the computer.

Another question, I want to use 4 channel ADC. Now the ADC for measuring battery voltage is OK.  nrf_drv_saadc_init returns error 0x08 when I Initialized another ADC as follow:

void saadc_init(void)
{
    ret_code_t err_code;


		nrf_saadc_channel_config_t channel_config_NTC = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN7);	
    err_code = nrf_drv_saadc_init(NULL, saadc_NTC_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(1, &channel_config_NTC);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);	


    nrf_saadc_channel_config_t channel_config_battery = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_VDD);			

    err_code = nrf_drv_saadc_init(NULL, saadc_Battery_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config_battery);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
		
}

Regards,

Alice

[ovrebekk]

Hi Alice

Jared is currently unavailable, and I will help you out in the mean time. 

You can't initialize the SAADC driver multiple times, nrf_drv_saadc_init(..) should only be called once. 

Typically the flow goes something like this:

1) First run nrf_drv_saadc_init(..) to initialize the peripheral

2) Run nrf_drv_saadc_channel_init(..) once for each channel that you want to use

3) Run nrf_drv_saadc_buffer_convert(..) to set up the buffers

4) Start sampling

Best regards
Torbjørn