RE: SAADC not as expected

PopradiArpad — Tue, 22 May 2018 14:58:34 GMT

Hi Alaa,

How can you use multiple channels with oversampling?

As you wrote above without oversampling the measured result is very noisy.

Thanks

RE: SAADC not as expected

Alaa — Sun, 15 Apr 2018 08:08:53 GMT

Hi,
I'm using SDK 14 and I'm using the configurations that appear in the ble_app_uart__saadc_timer_driven__scan_mode example here:
https://github.com/NordicPlayground/nRF52-ADC-examples
Here's my init function:

void saadc_init(void)
{
    ret_code_t err_code;
	
    nrf_drv_saadc_config_t saadc_config = NRF_DRV_SAADC_DEFAULT_CONFIG;
    saadc_config.resolution = NRF_SAADC_RESOLUTION_12BIT;
	
    nrf_saadc_channel_config_t channel_0_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);
    channel_0_config.gain = NRF_SAADC_GAIN1_6;
    channel_0_config.reference = NRF_SAADC_REFERENCE_VDD4;
	
    nrf_saadc_channel_config_t channel_1_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);
    channel_1_config.gain = NRF_SAADC_GAIN1_4;
    channel_1_config.reference = NRF_SAADC_REFERENCE_VDD4;
	
    nrf_saadc_channel_config_t channel_2_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN2);
    channel_2_config.gain = NRF_SAADC_GAIN1_4;
    channel_2_config.reference = NRF_SAADC_REFERENCE_VDD4;
	
    err_code = nrf_drv_saadc_init(&saadc_config, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_0_config);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_saadc_channel_init(1, &channel_1_config);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_saadc_channel_init(2, &channel_2_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0],SAADC_SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);   
    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1],SAADC_SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}

SAADC_SAMPLES_IN_BUFFER is 3 because I need to sample 3 ADC channels. You should adjust accordingly.

Also note the SAADC configurations in the sdk_config.h file (SAADC_ENABLED 1 , etc.)

About the resolution, there are 2 places:

1. in sdk_config.h: SAADC_CONFIG_RESOLUTION 2 //2 means 12 bit

2. in the saadc_init() function above: saadc_config.resolution = NRF_SAADC_RESOLUTION_12BIT

Make sure they're both set on the same resolution, although I think only #2 counts.

RE: SAADC not as expected

Yasser — Fri, 13 Apr 2018 08:57:13 GMT

Hi Alaa, I'm actually working on the SAADC of the nRF52, in the SDK 15.0.

Could you share with me the screen page of all the ADC configuration that you've made, because I don't know how to configure the Gain et the Resolution of my ADC,Thank you.

RE: SAADC not as expected

Alaa — Sun, 08 Apr 2018 12:54:08 GMT

Problem solved by oversampling 4x.

Changed SAADC_CONFIG_OVERSAMPLE from 0 to 2 in file sdk_config.h of ble_app upart.

Also I changed sample rate to 100ms to make it faster...

Here's the new sampling graph: