Garbage data when communicating between stm32 and esp32 using uart

[Sirin02]

When I send data from esp32 to stm32, it works fine. But when esp32 initially receives data from stm32 using uart, the data seems to have some random characters.

When i send 75, it looks like this in serial monitor:

Received: %$^#^12

Received: 12

Received: 12

I used KeilC and ArduinoIDE. I just want to get "Received: 12" from stm32. This is my code:

esp32:

#include <HardwareSerial.h>

#define UART_TX_PIN 17 //  TX
#define UART_RX_PIN 16 //  RX

int d1 = 7;
int d2 = 5;
char tx_array[10];

int flag = 0;

HardwareSerial SerialUART(2); // Create an instance of HardwareSerial for UART1

void setup() 
{
    Serial.begin(115200); // Initialize Serial Monitor for debugging
    SerialUART.begin(115200, SERIAL_8N1, UART_RX_PIN, UART_TX_PIN); // Initialize UART1
}

void loop()
{
  tx_array[0] = d1 + '0';
  tx_array[1] = d2 + '0';
  tx_array[2] = '\n'; // Line feed character
  //tx_array[3] = '\0'; // Null terminator

  SerialUART.print(tx_array);

   if (SerialUART.available()) {
        String receivedData = SerialUART.readStringUntil('\n'); // Read until newline
        if (receivedData != "") {
            // Process received data
            Serial.println("Received: " + receivedData);
        }
    }
  delay(500); // Add a small delay to prevent flooding the buffer
} 

 and stm32f103c8t6:

#include "main.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "stdio.h"
#include "string.h"
#include "stdlib.h"

/* USER CODE END Includes */

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

char tx_buffer[10] = {0};
char rx_buffer[10] = {0};
char rx_array[10] = {0};
char result[10] = {0};
int received_value1;
int received_value2;    

uint8_t count = 0;
uint8_t data = 0;
volatile uint32_t delayCounter = 0;
#define DELAY_THRESHOLD 500

UART_HandleTypeDef huart1;
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART1_UART_Init(void);

 
char* fuzzy_logic_func(char input_array[])
{
    input_array[strlen(input_array)] = '\0';
    received_value1 = input_array[0] - '0';              //char to int
    received_value2 = input_array[1] - '0';
    
    int result_var = received_value1 + received_value2;
    
    sprintf(result, "%d", result_var);
    strcat(result, "\n");
    delayCounter++;
    HAL_UART_Transmit(&huart1, (uint8_t*)result, strlen(result), 100);
    
    return result;
}


void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{   
    rx_buffer[count] = data;
    count++;
    
    if (data == 10)
    {
        for(int i = 0; i<10; i++)
        {
            rx_array[i] = rx_buffer[i];
            rx_buffer[i] = 0;
            //count = 0;
        }
        count = 0;
        
        fuzzy_logic_func(rx_array);
    }

    HAL_UART_Receive_IT(&huart1, &data, 1);
}

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_USART1_UART_Init();
  
  HAL_UART_Receive_IT(&huart1, &data, 1);
    
  while (1)
  {
if (delayCounter >= DELAY_THRESHOLD)
{
// Perform actions that were delayed
// Reset the delay counter
delayCounter = 0;
}
  }
}

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_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  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_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

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

/**
  * @brief USART1 Initialization Function
  * @param None
  * @retval None
  */
static void MX_USART1_UART_Init(void)
{

  /* USER CODE BEGIN USART1_Init 0 */

  /* USER CODE END USART1_Init 0 */

  /* USER CODE BEGIN USART1_Init 1 */

  /* USER CODE END USART1_Init 1 */
  huart1.Instance = USART1;
  huart1.Init.BaudRate = 115200;
  huart1.Init.WordLength = UART_WORDLENGTH_8B;
  huart1.Init.StopBits = UART_STOPBITS_1;
  huart1.Init.Parity = UART_PARITY_NONE;
  huart1.Init.Mode = UART_MODE_TX_RX;
  huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart1.Init.OverSampling = UART_OVERSAMPLING_16;
  if (HAL_UART_Init(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART1_Init 2 */

  /* USER CODE END USART1_Init 2 */

}

/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
/* USER CODE BEGIN MX_GPIO_Init_1 */
/* USER CODE END MX_GPIO_Init_1 */

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOA_CLK_ENABLE();

/* USER CODE BEGIN MX_GPIO_Init_2 */
/* USER CODE END MX_GPIO_Init_2 */
}

/* 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 */

[ONadr.1]

Check by oscilloscope or logic analyzer Tx signal from STM32. When you use internal oscillator, signal timing can be out of tolerace.Or some garbage is in the transmit buffer.