STM32F042: ADC conversion keeps getting ~.3 - .4V even with 0V input

Vu.Andy · ‎2017-11-13

Posted on November 13, 2017 at 20:43

I am not sure why I keep getting around .3 - .4 V even when the measured input is at 0V using a hand-held DMM. It's hard to imagine my ground noise is that high. Do you think it could be a software issue?

Here are the codes for reading ADC value. The reference voltage is 3.3V.

void StartADCConversion(void)

{

G_ADC_conv_ready = 0;

HAL_ADC_Start_IT(&L_hadc);

}

void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc)

{

double temp_volt = 0;

if (__HAL_ADC_GET_FLAG(hadc, ADC_FLAG_EOC))

{

temp_volt = HAL_ADC_GetValue(hadc);

G_PackVoltage = (temp_volt/4095.0) * 3.30;

G_ADC_conv_ready = 1;

}

waclawek.jan · ‎2017-11-13

Posted on November 13, 2017 at 22:06

Have you tried hard shorting the ADC input to VDDA?

JW

Vu.Andy · ‎2017-11-13

Posted on November 13, 2017 at 22:58

It seems like my conversion time is too short. I increase to ADC_SAMPLETIME_55CYCLES_5 and now it seems to work.

Thanks.