LAB: USART - Bluetooth

Date: 2025-09-26

Author/Partner:

Github: repository link

Demo Video: Youtube link

PDF version:

Introduction

In this lab, we will learn how to configure and use ‘USART(Universal synchronous asynchronous receiver transmitter)’ of MCU. Then, we will learn how to communicate between your PC and MCU and MCU to another MCU with wired serial communication.

Mission 1: Control LED(LD2) of each other MCU.
Mission 2: Run DC motors with Bluetooth

You must submit

LAB Report (*.md & *.pdf)
Zip source files(main*.c, ecRCC.h, ecGPIO.h, ecSysTick.c etc...).
- Only the source files. Do not submit project files

Requirement

Hardware

MCU
- NUCLEO-F411RE
Actuator/Sensor/Others:
- DC motor, DC motor driver(L9110s),
- Bluetooth Module(HC-06),

Software

Keil uVision, CMSIS, EC_HAL library

Preparation

Install the serial monitor: TeraTerm

Tutorial: USART with TeraTerm

Problem 1: EC HAL library

Using library

Option 1: Use the given library

Download the following files:

ecUART2.c
ecUART2.h

Option 2: Create your own library

Download the following files and fill in the empty spaces in the code.:

ecUART2_exercise_student.c
ecUART2_exercise_student.h

Then, change their names as

ecUART2.c
ecUART2.h

You must update your header files located in the directory EC\include\.

ecUSART2.h

// Configuration UART 1, 2 using default pins
void UART1_init(void);
void UART2_init(void);	
void UART1_baud(uint32_t baud);
void UART2_baud(uint32_t baud);

// USART write & read
void USART1_write(uint8_t* buffer, uint32_t nBytes);
void USART2_write(uint8_t* buffer, uint32_t nBytes);
uint8_t USART1_read(void);										
uint8_t USART2_read(void);	

// RX Interrupt Flag USART1,2
uint32_t is_USART1_RXNE(void);
uint32_t is_USART2_RXNE(void);

// Optional : Advanced Settings
// void USART_init(USART_TypeDef* USARTx, uint32_t baud);  		
// void UART_baud(USART_TypeDef* USARTx, uint32_t baud);	
// Example:
//     For BT serial : specific RX/TX pins 
//  USART_setting(USART1, PA_9,PA_10, BAUD_9600); 	// PA9 - RXD , PA10 - TXD

Problem 2: Communicate MCU1-MCU2 using RS-232

Procedure

1. Create a new project under the directory \repos\EC\LAB\LAB_USART_LED

The project name is “LAB_USART_LED”.
Create a new source files named as “LAB_USART_LED.c”

You MUST write your name on the source file inside the comment section.

2. Include your updated library in \repos\EC\include\ or \repos\EC\lib\ to your project.

ecUART2.h, ecUART2.c
Update ecSTM32F4v2.h

3. Connect each MCUs to each PC with USART 2 via USB cable (ST-Link)

MCU1 to PC1
MCU2 to PC2

4. Connect MCU1 to MCU2 with USART 1

connect RX/TX pins externally with jumper wires as
- MCU1_TX to MCU2_RXD
- MCU1_RX to MCU2_TX

Connect GND pins between MCU1-MCU2

MUST connect the same GND pin for MCU1 and MCU2

Send a message from PC_1 by typing keys on Teraterm. It should send that message from MCU_1 to MCU_2.

Note that you have to press "Enter" to end the message.

The received message by MCU_2 should be displayed on PC_2.
Turn other MCU's LED(LD2) On/OFF by sending text:

Press key "L" for Turn OFF LED
Press key "H" for Turn ON LED

Configuration

Type

Port - Pin

Configuration

System Clock

PLL 84MHz

USART2 : USB cable (ST-Link)

No Parity, 8-bit Data, 1-bit Stop bit, 38400 baud-rate

USART1 : MCU1 - MCU2

TXD: PA9 RXD: PA10

No Parity, 8-bit Data, 1-bit Stop bit, 38400 baud-rate

Digital Out: LD2

PA5

Example Code

Example codes for communicating between two USARTs

Example 1 : RX/TX one character at a time

Receive (Interrupt), Send (Polling)
Display my key input on PC monitor (myKeyboard-->USART2 --> Serial monitor)
Display the received message on PC monitor(USART1--> USART2 --> Serial monitor)

Example 2 : RX/TX a string

#include "ecSTM32F4v2.h"// this should include #include "ecUART2.h" 
//#include "ecUART2.h" 

static volatile uint8_t PC_Data = 0;
static volatile uint8_t BT_Data = 0;
uint8_t PC_string[]="Loop:\r\n";

void setup(void){
	RCC_PLL_init();
	SysTick_init();
	
	// USART2: USB serial init
	UART2_init();
	UART2_baud(BAUD_9600);

	// USART1: BT/MCU2 serial init 
	UART1_init();
	UART1_baud(BAUD_9600);
}

int main(void){	
	setup();
	printf("MCU Initialized\r\n");	
	while(1){
		// USART Receive: Use Interrupt only
		// USART Transmit:  Interrupt or Polling
		USART2_write(PC_string, 7);
		delay_ms(2000);        
	}
}

void USART2_IRQHandler(){          		// USART2 RX Interrupt : Recommended
	if(is_USART2_RXNE()){
		PC_Data = USART2_read();		// RX from UART2 (PC)
		USART2_write(&PC_Data,1);		// TX to USART2	 (PC)	 Echo of keyboard typing
		USART1_write(&PC_Data,1);	
	}
}


void USART1_IRQHandler(){          		// USART2 RX Interrupt : Recommended
	if(is_USART1_RXNE()){
		BT_Data = USART1_read();		// RX from UART1 (BT)		
		printf("RX: %c \r\n",BT_Data); // TX to USART2(PC)
	}
}

#include "ecSTM32F4v2.h"  // this should include #include "ecUART2.h" 

#define MAX_BUF 	10
#define END_CHAR 	13

static volatile uint8_t buffer[MAX_BUF]={0, };
static volatile uint8_t PC_string[MAX_BUF]={0, };
static volatile uint8_t PC_data = 0;

static volatile int idx = 0;
static volatile int bReceive =0;

void setup(void){
	RCC_PLL_init();
	SysTick_init();
	
	// USART2: USB serial init
	UART2_init();
	UART2_baud(BAUD_9600);

	// USART1: BT serial init 
	UART1_init();
	UART1_baud(BAUD_9600);
}

int main(void){	
	setup();
	printf("MCU Initialized\r\n");	
	
	while(1){
		if (bReceive == 1){
			printf("PC_string: %s\r\n", PC_string);				
			bReceive = 0;
		}
	}
}

void USART2_IRQHandler(){          		// USART2 RX Interrupt : Recommended
	if(is_USART2_RXNE()){
		PC_data = USART2_read();		// RX from UART2 (PC)
		USART2_write(&PC_data,1);		// TX to USART2	 (PC)	 Echo of keyboard typing
		
		// Creates a String from serial character receive				
		if(PC_data != END_CHAR && (idx < MAX_BUF)){	
			buffer[idx] = PC_data;
			idx++;
		}
		else if (PC_data== END_CHAR) {						
			bReceive = 1;
			// reset PC_string;
			memset(PC_string, 0, sizeof(char) * MAX_BUF);
			// copy to PC_string;
			memcpy(PC_string, buffer, sizeof(char) * idx);
			// reset buffer
			memset(buffer, 0, sizeof(char) * MAX_BUF);	
			idx = 0;
		}
		else{				//  if(idx >= MAX_BUF)			
			idx = 0;							
			// reset PC_string;
			memset(PC_string, 0, sizeof(char) * MAX_BUF);
			// reset buffer
			memset(buffer, 0, sizeof(char) * MAX_BUF);	// reset buffer
			printf("ERROR : Too long string\r\n");
		}
	}
}

Code

Your code goes here: ADD Code LINK such as github

Explain your source code with necessary comments.

// YOUR MAIN CODE ONLY
// YOUR CODE

Result

Experiment images and results

Show experiment images /results

Add demo video link

Problem 3: Control DC Motor via Bluetooth

Tutorial: Bluetooth

Follow the tutorial for Bluetooth setting.

Tutorial: Bluetooth

Search for the bluetooth module specification sheet (HC-06) and study the pin configurations.

The default PIN number is 1234.

Example of connecting to USART1

Procedure

1. Create a new project under the directory `\repos\EC\LAB\LAB_USART_Bluetooth

The project name is “LAB_USART_Bluetooth”.
Create a new source files named as “LAB_USART_Bluetooth.c”

You MUST write your name on the source file inside the comment section.

2. Include your updated library in \repos\EC\include\ or \repos\EC\lib\ to your project.

ecUART2.h, ecUART2.c
Update ecSTM32F4v2.h

3. Connect the MCU - BT module. Use USART 1

Connect RX/TX pins as
- MCU TX - BT RX
- MCU RX - BT TX

4. Connect the BT module (HC-06) in PC's bluetooth setting.

Check the Bluetooth connection by turning MCU's LED(LD2) ON/OFF by sending text of "0" or "1" from PC.
Connect 2 x DC motors to MCU/Motor Driver
Control motor by the Keyboard inputs

Press 'J' : To turn Left
- MotorA / MotorB = (50 / 80%) duty
Press 'L' : Turn Right
- MotorA / MotorB = (80 / 50%) duty
Press 'I' : Go straight
- MotorA / MotorB = (80 / 80 %) duty
Press 'K' : STOP
- MotorA / MotorB = (0 / 0 %) duty

You may use other the key inputs as your preference.

Configuration

Type

Port - Pin

Configuration

System Clock

PLL 84MHz

USART1 : MCU -Bluetooth

TXD: PA9 RXD: PA10

No Parity, 8-bit Data, 1-bit Stop bit, 9600 baud-rate

Digital Out: LD2

PA5

PWM (Motor A)

TIM2-Ch1

PWM period (2kHz~10kHz)

PWM (Motor B)

TIM2-Ch2

Code

Your code goes here: ADD Code LINK such as github

Explain your source code with necessary comments.

// YOUR MAIN CODE ONLY
// YOUR CODE

Result

Experiment images and results

Show experiment images /results

Add demo video link

Reference

Complete list of all references used (github, blog, paper, etc)

Troubleshooting

1. Cannot find my bluetooth module in my PC

Change your BT searching setting in your Window

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