Lots of ADC Noise with STM32F103RBT6 and STM32F103C8T6

[JanGE]

Hello,

i'm doing my first project with the STM32F103, where ADC is involved.

I want to read out several potentiometers and send MIDI commands to a PC.

So far everything is working, but there is soo much noise on the ADC data. I'm using only the upper 7 bits of the ADC data and even there it's constantly jumping between +-1% of the actual value, as soon the input is above 0V or under Vcc. I tested pots from 1-100kOhm, even a battery on the ADC input. On the oscilloscope the 3.3V had a +-2,5mV ripple, so i added capacitors, tested a LiIon Cell with 3.4V as input, same results.

I'm using a genuine Nucleo F103RBT6 and blue pill boards. Both with the same problem.

So I think, I'm doing anything wrong. Here is my code:

/* USER CODE BEGIN PV */
uint16_t adc_data[2];
/* USER CODE END PV */
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_DMA_Init(void);
static void MX_ADC1_Init(void);
int main(void)
{
  /* USER CODE BEGIN 1 */
 
  /* USER CODE END 1 */
 
  /* MCU Configuration--------------------------------------------------------*/
 
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
 
  /* USER CODE BEGIN Init */
 
  /* USER CODE END Init */
 
  /* Configure the system clock */
  SystemClock_Config();
 
  /* USER CODE BEGIN SysInit */
 
  /* USER CODE END SysInit */
 
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_USB_DEVICE_Init();
  MX_ADC1_Init();
  /* USER CODE BEGIN 2 */
  mimuz_init();
  HAL_Delay(5000);
  int  Wert, Wert2, controller;
  uint16_t adc_alt[2];
  uint8_t val[2];
    HAL_ADC_Start_DMA(&hadc1, (uint32_t*)adc_data, 2);
  HAL_ADCEx_Calibration_Start(&hadc1);
  HAL_ADC_Start(&hadc1);
  /* USER CODE END 2 */
 
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
	  HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13, GPIO_PIN_SET);
	  int i = 0;
	  for(;i<2;i++){
		  HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13, GPIO_PIN_SET);
		  if (adc_data[i]>>5 != adc_alt[i]){
			  controller = 14 + i;
			  sendCtlChange(0,controller,adc_data[i]>>5);
			  adc_alt[i] = adc_data[i]>>5;
		  }
	  }
	  processMidiMessage();
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */
}
 
 
static void MX_ADC1_Init(void)
{
 
  /* USER CODE BEGIN ADC1_Init 0 */
 
  /* USER CODE END ADC1_Init 0 */
 
  ADC_ChannelConfTypeDef sConfig = {0};
 
  /* USER CODE BEGIN ADC1_Init 1 */
 
  /* USER CODE END ADC1_Init 1 */
  /** Common config
  */
  hadc1.Instance = ADC1;
  hadc1.Init.ScanConvMode = ADC_SCAN_ENABLE;
  hadc1.Init.ContinuousConvMode = ENABLE;
  hadc1.Init.DiscontinuousConvMode = DISABLE;
  hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc1.Init.NbrOfConversion = 2;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    Error_Handler();
  }
  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_0;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_239CYCLES_5;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_1;
  sConfig.Rank = ADC_REGULAR_RANK_2;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN ADC1_Init 2 */
 
  /* USER CODE END ADC1_Init 2 */
 
}
 
/**
  * Enable DMA controller clock
  */
static void MX_DMA_Init(void)
{
 
  /* DMA controller clock enable */
  __HAL_RCC_DMA1_CLK_ENABLE();
 
  /* DMA interrupt init */
  /* DMA1_Channel1_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(DMA1_Channel1_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(DMA1_Channel1_IRQn);
 
}

I hope anyone can help me.

[TDK]

+/- 1% seems reasonable with a high impedance load. Averaging can typically get you 1-2 more bits of precision.

No silver bullet to get better results. Here you go:

https://www.st.com/resource/en/application_note/cd00211314-how-to-get-the-best-adc-accuracy-in-stm32-microcontrollers-stmicroelectronics.pdf

[prain]

According to the HAL_ADCEx_Calibration_Start function description:

"Perform an ADC automatic self-calibration

 *     Calibration prerequisite: ADC must be disabled (execute this

 *     function before HAL_ADC_Start() or after HAL_ADC_Stop() ).

 *     During calibration process, ADC is enabled. ADC is let enabled at

 *     the completion of this function."

so you should first calibrate ADC then start it: (line 41)

HAL_ADCEx_Calibration_Start(&hadc1);

HAL_ADC_Start_DMA(&hadc1, (uint32_t*)adc_data, 2);