NRF52832 ADC sampling mode

[NORDIC_SUR]

my ADC work in this mode :timer+PPI+SAADC   the ADC is 12bit

I init ADC like these code

void saadc_init(void)
{
    ret_code_t err_code;
	
    nrf_saadc_channel_config_t channel0_config =
            NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);// PIN and Channel config

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);// add callback funtion
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel0_config);//init channel
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0],SAMPLES_IN_BUFFER);//set convert 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);
}

sample every data 15us,and 16 data per channel

I only init one channel,and use the switch funtion to switch channel.the code like these

void ADC_swc(uint8_t channel)
{
	switch(channel)
	{
		case 0:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN0,NRF_SAADC_INPUT_DISABLED);break;
		case 1:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN1,NRF_SAADC_INPUT_DISABLED);break;
		case 2:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN2,NRF_SAADC_INPUT_DISABLED);break;
		case 3:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN3,NRF_SAADC_INPUT_DISABLED);break;
		case 4:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN4,NRF_SAADC_INPUT_DISABLED);break;
		case 5:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN5,NRF_SAADC_INPUT_DISABLED);break;
		case 6:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN6,NRF_SAADC_INPUT_DISABLED);break;
		case 7:nrf_saadc_channel_input_set(0,NRF_SAADC_INPUT_AIN7,NRF_SAADC_INPUT_DISABLED);break;
		default:;break;
	}
}

I found if I connect VCC to the ADC channel 1,

(1) the channel1 only first 8 data about 3600 but the later 8 data about 700,

(2) the channel2  is the later 8 data about 3600,first 8 data about 700.

question:I am not connect VCC to channel2,why channel2 have 3600

if I connect VCC to the ADC channel2,I also found the same phenomenon between channel 2 and channel 3

[Kenneth]

Hi,

If pins are unconnected and floating, then the input is undefined, and you can't rely on measurement (it may due to parasitic float up or down due to nearby circuitry or voltage).

Best regards,
Kenneth

[NORDIC_SUR]

I find another phenomenon,if I set sample 32 ADC data,the first 8 data is same as the laster 8 data of another channel.

[Kenneth]

I don't have any good explanation to that, are both buffers initialized as static?

Best regards,
Kenneth