ADC Measurement error in STM32F030C8

Question

Hi ST Community,

I am trying to measure system voltage (Lead Acid Battery) using ADC input of STM32F030C8 (PB1). The system voltage can be between 9V and 13.5V () so I am using voltage divider (10k and 1k) to lower the voltage to the 0 - 3.3V range. I am using STM32 Cube IDE. I am making ADC measurements/checking voltage in every 100ms.

The problem is I am getting huge fluctuations when reading the voltage. For example, I am getting values between ~11.8V and ~12.3V, when the system voltage is around 12.09V (checked with multimeter). I am not expecting to get exactly 12.09V, but 200 - 300mV offsets/errors are huge for me. I am calibrating the ADC channel before measurement but the error is same.

Could you please help me to this issue? Thank you in advance

/* USER CODE BEGIN Header */
/**
 ******************************************************************************
 * @file : main.c
 * @brief : Main program body
 ******************************************************************************
 * @attention
 *
 * Copyright (c) 2024 STMicroelectronics.
 * All rights reserved.
 *
 * This software is licensed under terms that can be found in the LICENSE file
 * in the root directory of this software component.
 * If no LICENSE file comes with this software, it is provided AS-IS.
 *
 ******************************************************************************
 */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include <stdio.h>
#include <string.h>
#include "stm32f0xx_hal.h"
#include <string.h>
#include <stdarg.h>
#include <math.h>
/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */


/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
 ADC_HandleTypeDef hadc;
DMA_HandleTypeDef hdma_adc;

I2C_HandleTypeDef hi2c2;

TIM_HandleTypeDef htim1;

/* USER CODE BEGIN PV */
uint8_t datacheck=0;

//-------------------ADC Variables-----------------------
float bat1, bat2, sysvolt;
uint16_t batteryvoltage1, batteryvoltage2, sysvoltage;





unsigned long long zero_millis=0;
unsigned long long time_start2 = 0;
unsigned long long time_start3 = 0;

unsigned long long time_start_battery_voltage=0;
unsigned long long batt_error_timer=0;



unsigned long long error_timer=0;

uint8_t powerMode=0; // 1 sebeke+ aku+, 2 sebeke- aku+


uint16_t Batt_error_ctr=0; // 0 NO Battery or battery is below 9.1V and 1 is battery is above 9.1V


/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_ADC_Init(void);
static void MX_DMA_Init(void);
static void MX_TIM1_Init(void);
static void MX_I2C2_Init(void);
/* USER CODE BEGIN PFP */
void adc_select_ch4 (void)
{
	ADC_ChannelConfTypeDef sConfig = {0};
	sConfig.Channel = ADC_CHANNEL_4;
	sConfig.Rank = 4;
	sConfig.SamplingTime = ADC_SAMPLETIME_13CYCLES_5;
	if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
	{
	Error_Handler();
	}
}

void adc_select_ch8 (void)
{
	ADC_ChannelConfTypeDef sConfig = {0};
	sConfig.Channel = ADC_CHANNEL_8;
	sConfig.Rank = 8;
	sConfig.SamplingTime = ADC_SAMPLETIME_13CYCLES_5;
	if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
	{
	Error_Handler();
	}
}

void adc_select_ch9 (void)
{
	ADC_ChannelConfTypeDef sConfig = {0};
	sConfig.Channel = ADC_CHANNEL_9;
	sConfig.Rank = 9;
	sConfig.SamplingTime = ADC_SAMPLETIME_13CYCLES_5;
	if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
	{
	Error_Handler();
	}
}

void adc_to_voltage(){
	sysvolt = adc_selenoid_voltage / 4095.0 * 3.3; // range 0 -3.1V
	bat2 = batteryvoltage2 / 4095.0 * 3.3 * 11; // range 9 - 13.5V
	bat1 = batteryvoltage1 / 4095.0 * 3.3 * 11; // range 9 - 13.5V
}

void read_batteries()
{
	HAL_ADCEx_Calibration_Start(&hadc);
	ADC1->CHSELR = ADC_CHSELR_CHSEL4;
	adc_select_ch4();
	HAL_ADC_Start(&hadc);
	HAL_ADC_PollForConversion(&hadc, 1000);
	sysvoltage = HAL_ADC_GetValue(&hadc);
	HAL_ADC_Stop(&hadc);

	HAL_ADCEx_Calibration_Start(&hadc);
	ADC1->CHSELR = ADC_CHSELR_CHSEL8;
	adc_select_ch8();
	HAL_ADC_Start(&hadc);
	HAL_ADC_PollForConversion(&hadc, 1000);
	batteryvoltage2 = HAL_ADC_GetValue(&hadc);
	HAL_ADC_Stop(&hadc);

	HAL_ADCEx_Calibration_Start(&hadc);
	ADC1->CHSELR = ADC_CHSELR_CHSEL9;
	adc_select_ch9();
	HAL_ADC_Start(&hadc);
	HAL_ADC_PollForConversion(&hadc, 1000);
	batteryvoltage1 = HAL_ADC_GetValue(&hadc);
	HAL_ADC_Stop(&hadc);
	adc_to_voltage();
}

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

/**
 * @brief The application entry point.
 * @retval int
 */
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_ADC_Init();
 MX_DMA_Init();
 MX_TIM1_Init();
 MX_I2C2_Init();
 /* USER CODE BEGIN 2 */
 HAL_TIM_Base_Start(&htim1);


 /* USER CODE END 2 */

 /* Infinite loop */
 /* USER CODE BEGIN WHILE */
 while (1)
 {
 /* USER CODE END WHILE */

 /* USER CODE BEGIN 3 */
	time_start3 = HAL_GetTick();
 if (time_start3 - time_start2 >= 100){
		read_batteries();
	}
 /* USER CODE END 3 */	
 }
}

/**
 * @brief System Clock Configuration
 * @retval None
 */
void SystemClock_Config(void)
{
 RCC_OscInitTypeDef RCC_OscInitStruct = {0};
 RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

 /** Initializes the RCC Oscillators according to the specified parameters
 * in the RCC_OscInitTypeDef structure.
 */
 RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI14|RCC_OSCILLATORTYPE_HSE;
 RCC_OscInitStruct.HSEState = RCC_HSE_ON;
 RCC_OscInitStruct.HSI14State = RCC_HSI14_ON;
 RCC_OscInitStruct.HSI14CalibrationValue = 16;
 RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
 RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
 RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL2;
 RCC_OscInitStruct.PLL.PREDIV = RCC_PREDIV_DIV1;
 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_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
 RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV2;
 RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;

 if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
 {
 Error_Handler();
 }
}

/**
 * @brief ADC Initialization Function
 * @PAram None
 * @retval None
 */
static void MX_ADC_Init(void)
{

 /* USER CODE BEGIN ADC_Init 0 */

 /* USER CODE END ADC_Init 0 */

 ADC_ChannelConfTypeDef sConfig = {0};

 /* USER CODE BEGIN ADC_Init 1 */

 /* USER CODE END ADC_Init 1 */

 /** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
 */
 hadc.Instance = ADC1;
 hadc.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
 hadc.Init.Resolution = ADC_RESOLUTION_12B;
 hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;
 hadc.Init.ScanConvMode = ADC_SCAN_DIRECTION_FORWARD;
 hadc.Init.EOCSelection = ADC_EOC_SEQ_CONV;
 hadc.Init.LowPowerAutoWait = DISABLE;
 hadc.Init.LowPowerAutoPowerOff = DISABLE;
 hadc.Init.ContinuousConvMode = DISABLE;
 hadc.Init.DiscontinuousConvMode = DISABLE;
 hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;
 hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
 hadc.Init.DMAContinuousRequests = ENABLE;
 hadc.Init.Overrun = ADC_OVR_DATA_PRESERVED;
 if (HAL_ADC_Init(&hadc) != HAL_OK)
 {
 Error_Handler();
 }

 /** Configure for the selected ADC regular channel to be converted.
 */
 sConfig.Channel = ADC_CHANNEL_4;
 sConfig.Rank = ADC_RANK_CHANNEL_NUMBER;
 sConfig.SamplingTime = ADC_SAMPLETIME_13CYCLES_5;
 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
 {
 Error_Handler();
 }

 /** Configure for the selected ADC regular channel to be converted.
 */
 sConfig.Channel = ADC_CHANNEL_8;
 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
 {
 Error_Handler();
 }

 /** Configure for the selected ADC regular channel to be converted.
 */
 sConfig.Channel = ADC_CHANNEL_9;
 if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
 {
 Error_Handler();
 }
 /* USER CODE BEGIN ADC_Init 2 */

 /* USER CODE END ADC_Init 2 */

}

/**
 * @brief I2C2 Initialization Function
 * @PAram None
 * @retval None
 */
static void MX_I2C2_Init(void)
{

 /* USER CODE BEGIN I2C2_Init 0 */

 /* USER CODE END I2C2_Init 0 */

 /* USER CODE BEGIN I2C2_Init 1 */

 /* USER CODE END I2C2_Init 1 */
 hi2c2.Instance = I2C2;
 hi2c2.Init.Timing = 0x2000090E;
 hi2c2.Init.OwnAddress1 = 0;
 hi2c2.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
 hi2c2.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
 hi2c2.Init.OwnAddress2 = 0;
 hi2c2.Init.OwnAddress2Masks = I2C_OA2_NOMASK;
 hi2c2.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
 hi2c2.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
 if (HAL_I2C_Init(&hi2c2) != HAL_OK)
 {
 Error_Handler();
 }

 /** Configure Analogue filter
 */
 if (HAL_I2CEx_ConfigAnalogFilter(&hi2c2, I2C_ANALOGFILTER_ENABLE) != HAL_OK)
 {
 Error_Handler();
 }

 /** Configure Digital filter
 */
 if (HAL_I2CEx_ConfigDigitalFilter(&hi2c2, 0) != HAL_OK)
 {
 Error_Handler();
 }
 /* USER CODE BEGIN I2C2_Init 2 */

 /* USER CODE END I2C2_Init 2 */

}

/**
 * @brief TIM1 Initialization Function
 * @PAram None
 * @retval None
 */
static void MX_TIM1_Init(void)
{

 /* USER CODE BEGIN TIM1_Init 0 */

 /* USER CODE END TIM1_Init 0 */

 TIM_ClockConfigTypeDef sClockSourceConfig = {0};
 TIM_MasterConfigTypeDef sMasterConfig = {0};

 /* USER CODE BEGIN TIM1_Init 1 */

 /* USER CODE END TIM1_Init 1 */
 htim1.Instance = TIM1;
 htim1.Init.Prescaler = 47;
 htim1.Init.CounterMode = TIM_COUNTERMODE_UP;
 htim1.Init.Period = 65535;
 htim1.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
 htim1.Init.RepetitionCounter = 0;
 htim1.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
 if (HAL_TIM_Base_Init(&htim1) != HAL_OK)
 {
 Error_Handler();
 }
 sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
 if (HAL_TIM_ConfigClockSource(&htim1, &sClockSourceConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
 if (HAL_TIMEx_MasterConfigSynchronization(&htim1, &sMasterConfig) != HAL_OK)
 {
 Error_Handler();
 }
 /* USER CODE BEGIN TIM1_Init 2 */

 /* USER CODE END TIM1_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);

}

/**
 * @brief GPIO Initialization Function
 * @PAram None
 * @retval None
 */
static void MX_GPIO_Init(void)
{
 GPIO_InitTypeDef GPIO_InitStruct = {0};

 /* GPIO Ports Clock Enable */
 __HAL_RCC_GPIOC_CLK_ENABLE();
 __HAL_RCC_GPIOF_CLK_ENABLE();
 __HAL_RCC_GPIOA_CLK_ENABLE();
 __HAL_RCC_GPIOB_CLK_ENABLE();

 /*Configure GPIO pin Output Level */
 HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13, GPIO_PIN_RESET);

 /*Configure GPIO pin Output Level */
 HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1|GPIO_PIN_15, GPIO_PIN_RESET);

 /*Configure GPIO pin Output Level */
 HAL_GPIO_WritePin(GPIOB, GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_15|GPIO_PIN_3
 |GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6|GPIO_PIN_7
 |GPIO_PIN_8|GPIO_PIN_9, GPIO_PIN_RESET);

 /*Configure GPIO pin : PC13 */
 GPIO_InitStruct.Pin = GPIO_PIN_13;
 GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

 /*Configure GPIO pins : PA1 PA15 */
 GPIO_InitStruct.Pin = GPIO_PIN_1|GPIO_PIN_15;
 GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

 /*Configure GPIO pins : PB12 PB13 PB15 PB3
 PB4 PB5 PB6 PB7
 PB8 PB9 */
 GPIO_InitStruct.Pin = GPIO_PIN_12|GPIO_PIN_13|GPIO_PIN_15|GPIO_PIN_3
 |GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6|GPIO_PIN_7
 |GPIO_PIN_8|GPIO_PIN_9;
 GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

 /*Configure GPIO pins : PA8 PA9 */
 GPIO_InitStruct.Pin = GPIO_PIN_8|GPIO_PIN_9;
 GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
 * @brief This function is executed in case of error occurrence.
 * @retval None
 */
void Error_Handler(void)
{
 /* USER CODE BEGIN Error_Handler_Debug */
 /* User can add his own implementation to report the HAL error return state */
 __disable_irq();
 while (1)
 {
 }
 /* USER CODE END Error_Handler_Debug */
}

#ifdef USE_FULL_ASSERT
/**
 * @brief Reports the name of the source file and the source line number
 * where the assert_param error has occurred.
 * @PAram file: pointer to the source file name
 * @PAram line: assert_param error line source number
 * @retval None
 */
void assert_failed(uint8_t *file, uint32_t line)
{
 /* USER CODE BEGIN 6 */
 /* User can add his own implementation to report the file name and line number,
 ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
 /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

PCarn.1 · Accepted Answer

You could increase the sampling time of your ADC channels from 13.5 to the biggest number possible. When the mux of the ADC switches channels there can be some transience, so in general the longer you can sample the better. You could also add oversampling to each channel. Lastly, you could try taking two samples on a channel, one right after another, then throw the first one away and keep the second one. All these are different ways to prevent any signals bleeding from one channel to another.

mƎALLEm · Answer

Hello,If you connect a constant voltage source directly to the ADC input channel to "emulate" your battery voltage, do you have the same behavior?PS: see this AN2834 "How to optimize the ADC accuracy in the STM32 MCUs". It may help you.

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