STM32 UART LED Control: Complete Tutorial with Code Examples | STM32 Programming Tutorial 4

Learn how to implement UART-based LED control on the STM32F401RE Nucleo-64 board. This comprehensive guide covers serial communication basics, GPIO configuration, and practical implementation using STM32CubeIDE.

Introduction

Serial communication is fundamental in embedded systems. In this tutorial, we'll control an LED using UART commands, demonstrating both digital output and serial communication concepts using the STM32F401RE microcontroller.

Hardware Requirements

- STM32F401RE Nucleo-64 board
- LED (any color)
- 330Ω resistor
- DB9 serial connector
- Jumper wires
- USB cable

Software Setup

- STM32CubeIDE
- Tera Term (terminal emulator)
- STM32 USB drivers

Implementation Steps

1. Hardware Connections

- Connect LED anode to PC8 through 330Ω resistor
- Connect LED cathode to GND
- UART connections:
- PA2 (USART2_TX) → DB9 RX
- PA3 (USART2_RX) → DB9 TX
- GND → DB9 GND

2. Software Configuration

- Clock: 16MHz HSI
- UART: 9600 baud, 8N1
- GPIO: PC8 as output

The main.c code for the STM32Cube is below.

#include "main.h"
#include <string.h>

UART_HandleTypeDef huart2;
uint8_t rx_data[1];
uint8_t welcome_msg[] = "UART LED Control\r\nPress 'H' for LED ON, 'L' for LED OFF\r\n";

void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_USART2_UART_Init();
  
  HAL_UART_Transmit(&huart2, welcome_msg, strlen((char*)welcome_msg), HAL_MAX_DELAY);
  HAL_GPIO_WritePin(GPIOC, GPIO_PIN_8, GPIO_PIN_RESET);

  while (1)
  {
    if(HAL_UART_Receive(&huart2, rx_data, 1, HAL_MAX_DELAY) == HAL_OK)
    {
      HAL_UART_Transmit(&huart2, rx_data, 1, HAL_MAX_DELAY);
      
      switch(rx_data[0])
      {
        case 'H':
        case 'h':
          HAL_GPIO_WritePin(GPIOC, GPIO_PIN_8, GPIO_PIN_SET);
          HAL_UART_Transmit(&huart2, (uint8_t*)"\r\nLED ON\r\n", 10, HAL_MAX_DELAY);
          break;
          
        case 'L':
        case 'l':
          HAL_GPIO_WritePin(GPIOC, GPIO_PIN_8, GPIO_PIN_RESET);
          HAL_UART_Transmit(&huart2, (uint8_t*)"\r\nLED OFF\r\n", 11, HAL_MAX_DELAY);
          break;
          
        default:
          HAL_UART_Transmit(&huart2, (uint8_t*)"\r\nInvalid Command!\r\n", 19, HAL_MAX_DELAY);
          break;
      }
    }
  }
}

Code Explanation

1. Configuration:
   - Uses UART2 at 9600 baud, 8-N-1
   - PC8 configured as output for LED
   - System clock set to 16MHz using HSI

2. **Program Flow**:
   - Initializes peripherals (UART, GPIO)
   - Sends welcome message
   - Sets LED initially OFF
   - Enters infinite loop for command processing

3. Main Loop Functions:
   - Waits for single character from UART
   - Echoes received character
   - Processes commands:
     - 'H'/'h': Turns LED ON
     - 'L'/'l': Turns OFF
     - Other: Shows error message

4. Key Functions Used:
   - `HAL_UART_Receive()`: Gets character from UART
   - `HAL_UART_Transmit()`: Sends response
   - `HAL_GPIO_WritePin()`: Controls LED state

This code demonstrates basic UART communication and GPIO control on STM32, suitable for beginners learning embedded programming.

3. Key Features

- Welcome message on startup
- LED control via 'H' and 'L' commands
- Command echo and feedback messages
- Input validation with error messages

Testing and Results

1. Open Tera Term
2. Configure serial port:
   - COM port: Your device
   - Baud rate: 9600
   - Data: 8-bit
   - Parity: None
   - Stop bits: 1
3. Commands:
   - Press 'H': LED turns ON
   - Press 'L': LED turns OFF

Video Tutorial

The following video shows how to configure UART using STM32Cube IDE, how the LED is turned on and off from the message received from the UART from PC using serial terminal.