ADC problems

[DCarr.1]

Hello all.

I have a custom stm32439VITx board running at 60MHz clocked off the HSI:

void SystemClock_Config(void)
{
 RCC_OscInitTypeDef RCC_OscInitStruct = {0};
 RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
 
 /** Configure the main internal regulator output voltage
 */
 
 __HAL_RCC_PWR_CLK_ENABLE();
 __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);
 
 /** Initializes the RCC Oscillators according to the specified parameters
 * in the RCC_OscInitTypeDef structure.
 */
 
 RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
 RCC_OscInitStruct.HSIState = RCC_HSI_ON;
 RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
 RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
 RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
 RCC_OscInitStruct.PLL.PLLM = 8;
 RCC_OscInitStruct.PLL.PLLN = 64;
 RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
 RCC_OscInitStruct.PLL.PLLQ = 4;
 
 if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
 {
  Error_Handler();
 }
 
 /** Initializes the CPU, AHB and APB buses clocks
 */
 
 RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
 |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
 RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
 RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
 RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
 RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
 if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
 {
  Error_Handler();
 }
}
 

with a signal driven by an amplifier into a 1K/1M resistor divider feeding into ADC1 channel 10 which I need to read every ten seconds or so:

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 */
  /** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
  */
  hadc1.Instance = ADC1;
  hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV6;
  hadc1.Init.Resolution = ADC_RESOLUTION_12B;
  hadc1.Init.ScanConvMode = DISABLE;
  hadc1.Init.ContinuousConvMode = ENABLE;
  hadc1.Init.DiscontinuousConvMode = DISABLE;
  hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
  hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc1.Init.NbrOfConversion = 1;
  hadc1.Init.DMAContinuousRequests = DISABLE;
  hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    Error_Handler();
  }
  /** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
  */
  sConfig.Channel = ADC_CHANNEL_10;
  sConfig.Rank = 1;
  sConfig.SamplingTime = ADC_SAMPLETIME_3CYCLES;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN ADC1_Init 2 */
  /* USER CODE END ADC1_Init 2 */
}

I've tried just about everything I can think of to get this to work, and I've got the code down to a simple test case:

static void test_adc() {
	HAL_Init();
	SystemClock_Config();
	MX_GPIO_Init();
	MX_ADC1_Init();
 
	HAL_ADC_Start(&hadc1);
 
	while(true) {
		HAL_Delay(1000);
 
		if(HAL_ADC_PollForConversion(&hadc1, 100) == HAL_OK) {
			static const float Vref = 3.3f;
			static const float R14 = 1000.0f;
			static const float R15 = 1000000.0f;
 
			const float adc = HAL_ADC_GetValue(&hadc1);
			const float vadc = adc * Vref / 4096.0f;
			const float vin = vadc * (R14 + R15) / R15;
 
			__NOP();
		}
	}
 
	HAL_ADC_Stop(&hadc1);
}

A voltmeter on the input pin is telling me 1200mV and the adc is reading between 890 and 910, which is an ajusted reading of around 720mV.

Like I say, I've tried all sorts of things to get a sensible reading, maybe there's something simple I'm missing. Is there anything obviously wrong with my code?

Thankyou

David

[Peter BENSCH]

Great, thanks for the feedback!

When your question is answered, please mark this topic as answered by choosing Select as Best for the preferred answer. This will help other users find that answer faster.

/Peter