wrong values after connecting over BLE

[Steffen Graf]

Hello,

I want to transfer analog values via BLE to a external Device. The SAADC is initialize for 2 channels, triggered by RTC-timer and i've get the right values from both channels. When i connect over BLE, the values i get change from ~12000 inc to ~9000 inc (14 bit resolution). Also after disconnecting the values are wrong until i restart the nrf.

My suppostion is a wrong Ramtable in Segger Studio, i have to change NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE, NRF_SDH_BLE_VS_UUID_COUNT

// <o> NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE - Attribute Table size in bytes. The size must be a multiple of 4. 
#ifndef NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE
#define NRF_SDH_BLE_GATTS_ATTR_TAB_SIZE 1900
#endif

// <o> NRF_SDH_BLE_VS_UUID_COUNT - The number of vendor-specific UUIDs. 
#ifndef NRF_SDH_BLE_VS_UUID_COUNT
#define NRF_SDH_BLE_VS_UUID_COUNT 20
#endif

in sdk_config.h and RAM_START=0x200026b8, RAM_SIZE=0xd948, because i have over 15 characteristics.

But when i read the softdevice spec, it must to be enough reserved ram.

SDK            15.3.0
Softdevice     6.1.1

[Jared]

Hi,

Steffen Graf said:

When i connect over BLE, the values i get change from ~12000 inc to ~9000 inc (14 bit resolution). Also after disconnecting the values are wrong until i restart the nrf.

Where do you check this? At the external device end or at the nRF? Could you show more of your code? 

regards

Jared 

[Steffen Graf]

Hello Jared,

i have check this on the nRF (see code line 215). Channel 1 is for battery voltage and at the second channel i use a MUX to get 4 values of force. I have checked my code without MUX and lower sample rate with the same result.

#include "saadc.h"
#include "hbconf.h"
#include "gyro.h"
#include "nrf.h"
#include "nrf_drv_clock.h"
#include "nrf_drv_rtc.h"

#define SAMPLES_IN_BUFFER ADC_AKKU+ADC_DMS

volatile uint8_t state = 1;
static bool INIT = false;
static uint8_t conf_ausbau = 0;
static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(3);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;
uint32_t              m_adc_evt_counter;
static uint8_t               saadc_funktion=0;
static uint32_t tz_AKKU = 500;                                    //Aktualisierungszeit in 100ms des Akkus
static uint32_t tz_DMS = 1;                                       //Aktualisierungszeit in 100ms des DMS
double realNull[AnzKraftAnlage+1] = {0.0};
double INA_Ref =990;                                       //Spannung bei 0V Brückenspannung am A2
double El_Limit =3000;                                     //max gewünschte Spannung am A2
double VDMS=3.0;                                           //Versorgungsspannung DMS
double Range;                                              //nutzbarer Spannungsbereich
double DMS_El_Range[AnzKraftAnlage+1];
double DMS_Mech_Range[AnzKraftAnlage+1];
double DMS_Faktor[AnzKraftAnlage+1];
double m_MechMin[AnzKraftAnlage+1];
double m_MechMax[AnzKraftAnlage+1];
double m_ElMin[AnzKraftAnlage+1];
double m_ElMax[AnzKraftAnlage+1];
double m_Gain;
double rohKraft = 0.00;
double alt_akku = 0.00;
double cal_sum=0;
double cs[200]={0};
int akkuMin=3000;
int m_mux_schritt=0;
int cal_funk=0;
int cal_zaehler=0;
bool cal_laeuft=false;
bool cal_null_laeuft=false;
nrf_ppi_channel_t saadc_buffer_swap_ppi_channel;

#define RTC_FREQUENCY 1024                          //Determines the RTC frequency and prescaler
#define RTC_CC_VALUE 8                            //Determines the RTC interrupt frequency and thereby the SAADC sampling frequency
#define SAADC_SAMPLE_INTERVAL_MS   1             //Interval in milliseconds at which RTC times out and triggers SAADC sample task 

const  nrf_drv_rtc_t           rtc = NRF_DRV_RTC_INSTANCE(2); /**< Declaring an instance of nrf_drv_rtc for RTC2. */
static uint32_t                rtc_ticks = RTC_US_TO_TICKS(SAADC_SAMPLE_INTERVAL_MS*1000, RTC_FREQUENCY);

#define DMS_SAMPLES_LEN 32
nrf_saadc_value_t dms_samples[AnzKraftAnlage+1][DMS_SAMPLES_LEN] = {0};
uint8_t dms_samples_next=0;

//globale Variablen der ADC's die zyklisch aktualisiert werden
uint8_t v_akku = 0;
uint32_t v_dms[AnzKraftAnlage+1] = {0};

void timer_handler(nrf_timer_event_t event_type, void * p_context)
{
  int i=0;                      ////DEBUG
}

void set_mux_schritt(int schritt)
{
  m_mux_schritt=schritt;
  memset(&dms_samples, 0, SAMPLES_IN_BUFFER);
}

static void lfclk_config(void)
{
    ret_code_t err_code = nrf_drv_clock_init();                        //Initialize the clock source specified in the nrf_drv_config.h file, i.e. the CLOCK_CONFIG_LF_SRC constant
    APP_ERROR_CHECK(err_code);
    nrf_drv_clock_lfclk_request(NULL);
}

static void rtc_handler(nrf_drv_rtc_int_type_t int_type)
{
    uint32_t err_code;
	
    if (int_type == NRF_DRV_RTC_INT_COMPARE0)
    {
        nrf_drv_saadc_sample();                                        //Trigger the SAADC SAMPLE task
		
        err_code = nrf_drv_rtc_cc_set(&rtc, 0, rtc_ticks, true);       //Set RTC compare value. This needs to be done every time as the nrf_drv_rtc clears the compare register on every compare match
        APP_ERROR_CHECK(err_code);
        nrf_drv_rtc_counter_clear(&rtc);                               //Clear the RTC counter to start count from zero
    }
}

void saadc_sampling_event_init(void)
{
     uint32_t err_code;

    //Initialize RTC instance
    nrf_drv_rtc_config_t rtc_config;
    rtc_config.prescaler = RTC_FREQ_TO_PRESCALER(RTC_FREQUENCY);
    err_code = nrf_drv_rtc_init(&rtc, &rtc_config, rtc_handler);                //Initialize the RTC with callback function rtc_handler. The rtc_handler must be implemented in this applicaiton. Passing NULL here for RTC configuration means that configuration will be taken from the sdk_config.h file.
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_rtc_cc_set(&rtc, 0, rtc_ticks, true);                    //Set RTC compare value to trigger interrupt. Configure the interrupt frequency by adjust RTC_CC_VALUE and RTC_FREQUENCY constant in top of main.c
    APP_ERROR_CHECK(err_code);

    //Power on RTC instance
    nrf_drv_rtc_enable(&rtc);                                                   //Enable RTC
}

void saadc_start_timer(void)
{
  nrf_drv_timer_enable(&m_timer);
}

void saadc_stop_timer(void)
{
  nrf_drv_timer_disable(&m_timer);
}

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

uint8_t get_v_akku(void)
{
   return v_akku;
}

uint32_t get_v_dms(int index)
{
   return v_dms[index];
}

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
  double akku_tmp, test;
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;
//        saadc_stop_timer();
        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        // Abfrage Akkuspannung
       
        if (m_adc_evt_counter % tz_AKKU==0)
        {
          switch (saadc_funktion)
          {
            //VCH_IN 5V in mV
            case 1:
              v_akku=(uint8_t)(1650.0 / 16384.0 * p_event->data.done.p_buffer[0] / 0.167);
              break;

            case 2:
              //Berechnung des Ladestroms in % (100%=300mA)
              v_akku=(uint8_t)((1650.0 / 16384.0 * p_event->data.done.p_buffer[0])/2.632*1/3);       //0.002632V entspricht 1mA Ladestrom
              int z=v_akku;
              break;

            case 3:
              test=p_event->data.done.p_buffer[0];
              akku_tmp=((( p_event->data.done.p_buffer[0] / 16384.0 * 1650.0 / 0.272)-akkuMin)/1110.0*100);
              alt_akku=(akku_tmp*0.3+ alt_akku*0.7);
              v_akku=(uint8_t) alt_akku;
              if (v_akku>100)
                v_akku=100;
              if (v_akku<0)
                v_akku=0;
              break;

            case 4:
              v_akku=(uint8_t)(420.0 / 16384.0 * p_event->data.done.p_buffer[0]);
              break;

            case 5:
              v_akku=(uint8_t)(420.0 / 16384.0 * p_event->data.done.p_buffer[0]);
              break;

            case 6:
              v_akku=(uint8_t)(420.0 / 16384.0 * p_event->data.done.p_buffer[0]);
              break;

            default:
              v_akku=0;
              break;
          }
        }
       
        
        double dms_avg = 0.0;
        double mw=0;
        int i=0;
        if (m_adc_evt_counter % tz_DMS==0)
        {
          dms_samples[m_mux_schritt][dms_samples_next] = p_event->data.done.p_buffer[1];
          if (dms_samples_next == DMS_SAMPLES_LEN-1) dms_samples_next=0; else dms_samples_next++;
          
          for (i=0;i<DMS_SAMPLES_LEN;i++)
          {
            dms_avg += dms_samples[m_mux_schritt][i];
          }
          dms_avg/=DMS_SAMPLES_LEN;

          if (m_mux_schritt<AnzahlKraftCh)                                 //Kraftsensor
          {
            rohKraft=1650.0/16384.0*dms_avg;                            // 14 bit resolution  1.65V / 2^14bits * increments= Value in mV
            mw=(rohKraft-realNull[m_mux_schritt])/((m_ElMax[m_mux_schritt]-m_ElMin[m_mux_schritt])*m_Gain)*(DMS_Mech_Range[m_mux_schritt]*1000.0)*1.0389;
            v_dms[m_mux_schritt]=mw*0.05+ v_dms[m_mux_schritt]*0.95;
            //v_dms[m_mux_schritt]=rohKraft;              /////DEBUG

            if(m_adc_evt_counter % 1 == 0)
            {
              SEGGER_RTT_printf(0,"Kraft=%d   Anlage1=%d    Anlage2=%d    Anlage3=%d\n", (int)rohKraft, (int)get_v_dms(1), (int)get_v_dms(2), (int)get_v_dms(3));
            }
          }
          else                                                             //Anlagesensor
          {
            v_dms[m_mux_schritt]=dms_avg*0.05+v_dms[m_mux_schritt]*0.95;
          }
        }

    }
    
    if (m_adc_evt_counter>=1000)
    {
      m_adc_evt_counter=0;
    }
    else
    {
      m_adc_evt_counter++;
    }
}

void saadc_init(uint8_t variante)
{
  conf_ausbau = conf_ausbau | variante;
  if (INIT !=true)
  {
    ret_code_t err_code;
  
  //Init Analogeingang Akku
    nrf_saadc_channel_config_t channelAkku_config =
        HB_DRV_SAADC_AKKU_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN5);

     //Init Analogeingang DMS
    nrf_saadc_channel_config_t channelDMS_config =
        HB_DRV_SAADC_DMS_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN2); 

    static const nrfx_saadc_config_t hb_config = NRFX_SAADC_HB_CONFIG;
       
    err_code = nrf_drv_saadc_init(&hb_config, saadc_callback);
    APP_ERROR_CHECK(err_code);

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

    err_code = nrf_drv_saadc_channel_init(1, &channelDMS_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);
  
    INIT=true;
  }

}

void saadc_start()
{
    twi_init();                       //falls noch nicht geschehen den I2c initialisieren
    lfclk_config();                                  //Configure low frequency 32kHz clock
    saadc_sampling_event_init();                                    //Configure RTC. The RTC will generate periodic interrupts. Requires 32kHz clock to operate.

    saadc_init(1);                                    //Initialize and start SAADC
}

here my debug window after restart

and here after connection over BLE

[Jared]

Do you observe the same if you try to measure something external from the PCB such as a voltage from a bench top supply? Also, do you do any sorts of calibration after a connection event? 

[Steffen Graf]

Sorry for the late answer, i have to do another project first. I have checked my hardware and the voltage at the analog inputs are correct. But i found out, that the buffer values are swap when i reconnect or write to a BLE characteristic. Is there any way to prevent that?

[Jared]

Hi,

Steffen Graf said:

But i found out, that the buffer values are swap when i reconnect or write to a BLE characteristic. Is there any way to prevent that?

It sounds very similar to this issue. Please try the suggested solution in that thread.

best regards

Jared