How does 52840 use SAADC to sample voltage?

Question

Hi, 
 I'm using the SAADC to sample external voltage to fill in the battery service. I have use APP_TIMER_DEF to create a timer to do it every 30 seconds. Also I have init the adc: 
 void saadc_init(void){
ret_code_t err_code;
nrf_saadc_channel_config_t channel_config =
NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN7);

err_code = nrf_drv_saadc_init(NULL, saadc_callback);
APP_ERROR_CHECK(err_code);

err_code = nrf_drv_saadc_channel_init(7, &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);}
 
 But I couldn't find the function start the ADC and how to get the sample result in the ADC interrupt? Could anyone tell me? Thanks

Jørgen Holmefjord · Accepted Answer

Hi, 
 This is shown in the SAADC peripheral example in our SDK. 
 The example works in the following way: 
 
 SAADC peripheral is configured and channels and buffers are setup. The example use double-buffering, meaning that one buffer is used for sampling while the other (filled) buffer is processed. 
 Timer is setup to trigger an event every 400 ms. The timer event is connected to the SAADC sample task through a PPI channel. On every timer event, the sample task is called, triggering a single sample. 
 When the SAADC sample task have been called SAMPLES_IN_BUFFER times, the buffer will be full, triggering the SAADC callback ( saadc_sampling_event_init ). The content of the buffer is printed using NRF_LOG, before the buffer is setup for sampling again. 
 
 If you want lower power, you can check out the SAADC low-power example on our GitHub. This example use RTC for low power, and also include calibration for increased sampling accuracy. 
 Best regards, 
 Jørgen