STM32G431KB ADC Wrong value

[cppoisson]

Hi everyone,

I am using the ADC2 of the STM32G431KB to read a voltage value. I am actualy measuring 0.8V on the pin of the ADC with a multimeter, but while debuging, the conversion give me back 0.12V (~150 from the ADC, instead of ~1000). 

This is my config and the way I do the conversion. 

void MX_ADC2_Init(void)
{

  /* USER CODE BEGIN ADC2_Init 0 */

  /* USER CODE END ADC2_Init 0 */

  ADC_ChannelConfTypeDef sConfig = {0};

  /* USER CODE BEGIN ADC2_Init 1 */

  /* USER CODE END ADC2_Init 1 */

  /** Common config
  */
  hadc2.Instance = ADC2;
  hadc2.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV4;
  hadc2.Init.Resolution = ADC_RESOLUTION_12B;
  hadc2.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc2.Init.GainCompensation = 0;
  hadc2.Init.ScanConvMode = ADC_SCAN_ENABLE;
  hadc2.Init.EOCSelection = ADC_EOC_SEQ_CONV;  
  hadc2.Init.LowPowerAutoWait = DISABLE;
  hadc2.Init.ContinuousConvMode = ENABLE; 
  hadc2.Init.NbrOfConversion = 2;
  hadc2.Init.DiscontinuousConvMode = DISABLE;
  hadc2.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc2.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  hadc2.Init.DMAContinuousRequests = ENABLE;
  hadc2.Init.Overrun = ADC_OVR_DATA_PRESERVED;
  hadc2.Init.OversamplingMode = DISABLE;
  if (HAL_ADC_Init(&hadc2) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_VOPAMP2;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_640CYCLES_5;
  sConfig.SingleDiff = ADC_SINGLE_ENDED;
  sConfig.OffsetNumber = ADC_OFFSET_NONE;
  sConfig.Offset = 0;
  if (HAL_ADC_ConfigChannel(&hadc2, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_VOPAMP3_ADC2;
  sConfig.Rank = ADC_REGULAR_RANK_2;
  sConfig.SamplingTime = ADC_SAMPLETIME_640CYCLES_5;
  sConfig.SingleDiff = ADC_SINGLE_ENDED;
  sConfig.OffsetNumber = ADC_OFFSET_NONE;
  sConfig.Offset = 0;
  if (HAL_ADC_ConfigChannel(&hadc2, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }

  if(HAL_ADCEx_Calibration_Start(&hadc2, ADC_SINGLE_ENDED) != HAL_OK){
    Error_Handler();
  }


  /* USER CODE BEGIN ADC2_Init 2 */
  HAL_ADC_Start_DMA(&hadc2, (uint32_t *) &analog_input.unmap[2], 2);
  /* USER CODE END ADC2_Init 2 */

}

float ll_motor_GetVoltage(void) {
    return (((float)analog_input.voltage * VREF_ADC) / (ADC_RESOLUTION));
}

The input_voltage is linked to the first chanel (VOPAMP 2) of the ADC and put in analog_input.unmap[2] by the dma. 
VREF_ADC = 3.3f
ADC_RESOLUTION = 4096 (12bits)


Do you have an idea on the wrong value origin ? 

Best regards,

Clément.

[Andrew Neil]

Duplicate?

https://community.st.com/t5/stm32-mcus-products/stm32g431kb-adc-wrong-value/td-p/720375

---

@cppoisson wrote:

the ADC is not giving back the right voltage value (which is 0.8V measured with a multimeter) !

---

So what value is it giving?

Note that a multimeter will give a (relatively) long-term averaged reading, whereas the ADC will give an instantaneous sample ...

See also: https://community.st.com/t5/stm32-mcus-boards-and-hardware/adc-voltage-drop/m-p/722300 

[cppoisson]

I created a new topic because I found new details on the problem that I don't undertstand. I didn't notify that if disabled the ContinuousConvMode I had the wright value on the ADC (900 on the ADC equal to 790mV), but the value is not updated. When I am using the ContinuousConvMode the value from the ADC is 150 so 120mV, but this value is updated. 

I also measure the voltage with the osciloscope, I also found a DC 800mV Voltage.

[Andrew Neil]

---

@cppoisson wrote:

I created a new topic because I found new details on the problem 

---

It makes more sense keep all of the details of the problem in one place, and all of the existing contributors informed.

Merged into the original thread

[MasterT]

I noticed 

  HAL_ADC_Start_DMA(&hadc2, (uint32_t *) &analog_input.unmap[2], 2);

correct code to call adc_dma:

  if (HAL_ADC_Start_DMA(&hadc2, (uint32_t *)inp_1, (2 * INP_BUFF)) != HAL_OK) {

 If you post how analog_input.unmap[2] declared in the initial post it would be easier to spot software error.