How to configure ADC in single end mode and also how to control my samplerate using local timer?

[vishal]

Hello, I am using nRF52832 DK, and implement my software using eclipse with ARM GCC complier sdk12.1. I have interface accelerometer sensor with this board. I have read SAADC and send adc value to android apps. I am using 12 bit ADC, But problem is for calibrating acceleration analog value. So I want to use single ended mode for ADC and how to select mode for control the sample rate using CC. I read data sheet for controlling sample rate, but unable to understand what's I need to change in my program. nRF52832 data sheet is in given like this (Capture and compare value. Sample rate is 16 MHz/CC). So please help me for how to configure my program with above changes let me know., or can you give me some reference link tutorial.......

Thanks in Advanced......

[Jørgen Holmefjord]

Do you mean you want to use the SAMPLERATE register to control the sampling? We don't have any example or tutorial on this, as most use timer/RTC to trigger the sample task. This gives better flexibility, as SAMPLERATE registers CC value is limited from 80 to 2047. What you need to change in your code depends on your code. Could you post your code and/or describe your setup in more detail?

[vishal]

Thank you sir for giving me reply. let me explain what actually I have faing problem. I have using ADXL335 accelerometer sensor and I have successfully read three axis X Y Z by 12 bit SAADC and also send this to BLE. Actual sensor data is coming but sir I need to increase sampling rate upto 24575 point for each analog channel. my ADC is in scan mode I have use only three channel for X y and z axis. When I increase sampling rate and covert to micro second BLE is not connect with my apps. Please sir how to solved this problem. and one if the another problem is I am not able to send 12 bit value for the range of 0-4095. Its only 8 bit data send not see properly my three axis value. Please tell me sir how to convert uint_8 array into uint16_t bit array. I am search lots of tutorial and community it said it say like this --> value[i2] = adc_value; value[(i2)+1] = adc_value >> 8; why need to right shift by 8 bit. for sending data data over ble. please sir let me know. And I know your support is very good and quick response with question.. My ADC code is

void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);
    APP_ERROR_CHECK(err_code);
}

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;
        uint16_t adc_value;
      //  uint16_t value1[SAADC_SAMPLES_IN_BUFFER*2];
        uint8_t value[SAADC_SAMPLES_IN_BUFFER*2]; // own change uint8_t
        uint8_t bytes_to_send;
//        uint16_t data[3];
     
        // set buffers
        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAADC_SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        // print samples on hardware UART and parse data for BLE transmission
        printf("ADC event number: %d\r\n",(int)m_adc_evt_counter);
        for (int i = 0; i < SAADC_SAMPLES_IN_BUFFER; i++)
        {
            printf("%d\r\n", p_event->data.done.p_buffer[i]);
             adc_value = p_event->data.done.p_buffer[i];
//             for (int j = 0; j <24576; j++)
//             {
//            	 data = adc_value;
//             }
//            adc_value = 4095;
            value[i*2] = adc_value;
            value[(i*2)+1] = adc_value >> 8;

        }
				
        // Send data over BLE via NUS service. Makes sure not to send more than 20 bytes.
        if((SAADC_SAMPLES_IN_BUFFER*2) <= 20)
        {
            bytes_to_send = (SAADC_SAMPLES_IN_BUFFER*2);
        }
        else 
        {
            bytes_to_send = 20;
        }


        err_code = ble_nus_string_send(&m_nus, value, bytes_to_send);
        if (err_code != NRF_ERROR_INVALID_STATE) 
        {
            APP_ERROR_CHECK(err_code);
        }
						
        m_adc_evt_counter++;
    }
}

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_AIN4);
    channel_0_config.gain = NRF_SAADC_GAIN1_4;
    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_AIN5);
    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_AIN6);
    channel_2_config.gain = NRF_SAADC_GAIN1_4;
    channel_2_config.reference = NRF_SAADC_REFERENCE_VDD4;
	
//    nrf_saadc_channel_config_t channel_3_config =
//        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN7);
//    channel_3_config.gain = NRF_SAADC_GAIN1_4;
//    channel_3_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_channel_init(3, &channel_3_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);
}

[Jørgen Holmefjord]

From the SAADC documentation: "The SAMPLERATE timer mode cannot be combined with SCAN mode, and only one channel can be enabled in this mode." You need to use TIMER/RTC to achieve what you want. Please have a look at the SAADC example in the SDK, or these examples on our GitHub. The reason you need to shift the value before sending it over BLE using NUS, is that this is used for sending chars, which is only 8 bits. You need to shift the upper 8 bits of the 16 bit variable down to the lower 8 bits, for it to be stored in a char.

[vishal]

Thanks sir for giving me your valuable reply now I am understand why we need to shift 16 bit to 8 bit for sending via BLE using NUS. Now sir one more question I have using sdk13.1 for nRF52832. now we develop our own mobile apps for android. As off now it is directly connect no need to type any key. So sir but I need to add in my above adc program static pass key. I have read lots of tutorial and also change in my program. Paring request is send but not get response for type pass key. It said unable to connect or invalid pass or static key. So sir let me know some example for how to add static pass key for nRF52 series I have using PCA10040 Board.

Thanks sir...... Vishal

[Jørgen Holmefjord]

Please have a look at the thread linked in this comment, and my comment below.