How to increase the accuracy of ADC channel

[arshdeep]

Hi,

I am reading a voltage value from an analog sensor which changes values with 0.02V step. So, i need the accuracy up to 0.02V from ADC channels . But right now i am off by around 0.05V. Where I should get 2.94V I am receiving 2.89V and this changes the sensor value drastically.  I am already using 14 bit resolution. How else can i increase the accuracy ? 

I am using single ended with no over-sampling with a gain of 1/6, reference 0.6.

If I try to enable the over-sampling . I face an unusual behavior that the debugger goes in NO BREAKPOINT CONDITION.

Could there be a fault in my code? May be because of type casting , i am loosing accuracy ??

Please Suggest!!

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[5];
float T, T1, T2, P1, P2;

uint8_t nus_to_send_array[2];

//err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAADC_SAMPLES_IN_BUFFER);
//APP_ERROR_CHECK(err_code);

int i;
NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);

for (i = 0; i < SAADC_SAMPLES_IN_BUFFER; i++) {
// printf("%d\r\n",p_event->data.done.p_buffer[i]);
adc_value[i] = p_event->data.done.p_buffer[i];
}

P2 = (adc_value[4]) / 4551.11; // CONVERT ADC VALUE TO VOLTAGE 

}

[haakonsh]

You'll need to use oversampling if you want a high degree of accuracy. What is the sensors output voltage range? I ask because you might find it useful to use differential inputs where the "negative" input is biased, f.ex. to 2.5V. That way your 14 bits will cover a smaller voltage range and thus give you greater resolution.

For your issue we need to find the function that issued the error code. The breakpoint you hit is inside the applications error handler that is called whenever a APP_ERROR_CHECK is run in a err_code that is not NRF_SUCCESS.
We need the error code, line number, and file name that is passed to the error handler.