ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

Karl Ylvisaker — Thu, 21 Sep 2023 16:06:42 GMT

Hello,

nrfx_saadc_sample() returning NRF_ERROR_INVALID_STATE means that the SAADC is in the IDLE state when you attempt to call nrfx_saadc_sample().
Please make sure to have started the SAADC before you attempt to sample, and see if this resolves your issue.
Please also make sure that your calibrateoffset procedures follows the approach described in the workaround for Errata 86.

Best regards,
Karl

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

Laerte Junior — Wed, 20 Sep 2023 12:24:57 GMT

Hi,

[quote userid="65515" url="~/f/nordic-q-a/103882/adc-values-are-changing-each-time-you-assemble-or-disassemble-or-tighten-the-screws-of-a-mechanical-assembly/446524"]Yes, doing the SAADC internal calibration (once or periodically) would help. Couple of tickets which might help, hard to find the best as there are so many:[/quote]

I tried to do it using the example code of the "continuous-adc-sampling-issue", where I inserted the calibration function in my saadc_init, but now, I have problems with my saadc_event_handler function.

below, my modified function:

void saadc_init(void) {
    // SAADC config & calibrate
    nrfx_saadc_config_t saadc_config = NRFX_SAADC_DEFAULT_CONFIG;
    APP_ERROR_CHECK(nrfx_saadc_init(&saadc_config, saadc_event_handler));
    while (nrfx_saadc_is_busy())
        sd_app_evt_wait();

    // Channels config
    //Bateria
    nrf_saadc_channel_config_t battery_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);//NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_VDD);
    APP_ERROR_CHECK(nrf_drv_saadc_channel_init( 0, &battery_config));

    //Celulas de carga
    nrf_saadc_channel_config_t cell_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_DIFFERENTIAL(NRF_SAADC_INPUT_AIN4, NRF_SAADC_INPUT_AIN7);
    cell_config.reference = NRF_SAADC_INPUT_AIN5;
    cell_config.gain = NRF_SAADC_GAIN1_4;
    APP_ERROR_CHECK(nrf_drv_saadc_channel_init( 1, &cell_config));

    // double buffering
    APP_ERROR_CHECK(nrfx_saadc_buffer_convert(buffer[0], INPUTS));
    APP_ERROR_CHECK(nrfx_saadc_buffer_convert(buffer[1], INPUTS));

// Calibrate the SAADC by finding its offset
    NRF_SAADC->TASKS_CALIBRATEOFFSET = 1;
    while (NRF_SAADC->EVENTS_CALIBRATEDONE == 0);
    NRF_SAADC->EVENTS_CALIBRATEDONE = 0;
    while (NRF_SAADC->STATUS == (SAADC_STATUS_STATUS_Busy << SAADC_STATUS_STATUS_Pos));
}

This form is correct?

The returned error of the saadc_timeout_handler is:

<error> app: ERROR 8 [NRF_ERROR_INVALID_STATE]

static void saadc_timeout_handler(void *p_context) { // ADC for battery status
UNUSED_PARAMETER(p_context);
APP_ERROR_CHECK(nrfx_saadc_sample());
}

Regards

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

hmolesworth — Mon, 18 Sep 2023 19:09:05 GMT

Yes, doing the SAADC internal calibration (once or periodically) would help. Couple of tickets which might help, hard to find the best as there are so many:

continuous-adc-sampling-issue

trying-to-understand-saadc-changes

Edit: AIN4, AIN5 and AIN7 require small caps to GND close to nRF52 pins, maybe 10nF or 100nF as a minimum; also try 12-bit resolution if using 10-bit

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

Laerte Junior — Mon, 18 Sep 2023 18:31:07 GMT

I removed r1 and r2 resistors, but the adc values continue changing after any mechanic modifications.

[quote userid="65515" url="~/f/nordic-q-a/103882/adc-values-are-changing-each-time-you-assemble-or-disassemble-or-tighten-the-screws-of-a-mechanical-assembly/446514"]Edit: If power is removed or restored then the SAADC needs recalibrating, sorry I should have thought of suggesting that[/quote]

I agree, but I'm not using it in my code calibrations functions that found in nrfx_saadc.c. I need use it?

below my code that read adc values.

#define AMOSTRAS_DIVISAO 50

void saadc_event_handler(nrfx_saadc_evt_t const *p_event) {

    ret_code_t err_code;
    int16_t sample_ADC;

    if (p_event->type == NRFX_SAADC_EVT_DONE){
       nrf_saadc_value_t *adc_result = p_event->data.done.p_buffer;
       uint16_t mv = adc_to_mv(adc_result[0]);
       battery_level = battery_level_in_percent(mv);

       APP_ERROR_CHECK(nrfx_saadc_buffer_convert(adc_result, INPUTS));

       RESbatt = adc_result[0]; //tensao da bateria
       sample_ADC = adc_result[1];

       if(m_scale.calibrating == true)
       {
           vetor_adc[index_vetor++] = sample_ADC;//REScell;
           if (index_vetor>=AMOSTRAS_DIVISAO)
           {
               index_vetor = 0;
               m_scale.calibrating = false;
            }
           adc_cell_sum=0;
           for (int i=0; i<AMOSTRAS_DIVISAO; i++)
           {
               adc_cell_sum += vetor_adc[i];
           }

           adc_leitura = (adc_cell_sum/AMOSTRAS_DIVISAO); //calculo do offset
           m_scale.offset = adc_leitura;
       }
       REScell = sample_ADC;
       err_code = ble_bas_battery_level_update(&m_bas, battery_level, BLE_CONN_HANDLE_ALL);

       if ((err_code != NRF_SUCCESS)&&(err_code != NRF_ERROR_INVALID_STATE)&&(err_code != NRF_ERROR_RESOURCES)&&(err_code != NRF_ERROR_BUSY)&&(err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING))
       {
           APP_ERROR_HANDLER(err_code);
       }
    }
}

the saadc_event_handler function iscalled every 5ms.

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

hmolesworth — Mon, 18 Sep 2023 17:31:56 GMT

Let's assume the 3V supply changes (for whatever reason); this will change the differential output of the bridge. Using the 3V supply as the reference for the SAADC on NRF_SAADC_INPUT_AIN5 which does not change by the same percentage as the bridge supply introduces an unwanted change in bridge output because the bridge supply is not the 3V supply but (350/550)*3=1.9V. Using a similar derived value for the SAADC reference would then track the changing bridge excitation voltage. Worth a try; or just get rid of the two 100R resistors R1 and R2 and see if that helps

Edit: If power is removed or restored then the SAADC needs recalibrating, sorry I should have thought of suggesting that

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

Laerte Junior — Mon, 18 Sep 2023 16:56:48 GMT

The base is very rigid and very tight. The strain gauges that I'm using already have temperature compensation. Below. the schematic of my project where the bridge circuit is conected.

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

hmolesworth — Mon, 18 Sep 2023 16:18:36 GMT

Perhaps check that NRF_SAADC_INPUT_AIN5 is derived from +3V bridge excitation and not INA333 1.5V reference or ensure INA333 1.5V reference tracks +3V bridge excitation otherwise bridge measurement is differential but not not ratiometric and therefore varies with bridge excitation. Also bridge arm resistance (and hence load on the +3V bridge excitation) varies as the assembly is flexed with changes in screw tightness if the base is not rigid.

ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values ​​are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly

RE: ADC values are changing each time you assemble or disassemble or tighten the screws of a mechanical assembly