STM32 DHT11 MPU6050 LCD Multi-Sensor Project

Video Demonstrations

Hardware Demo

hardware_demo.mp4

UART Output

Hterm_uart_output.mp4

When the button is pressed, the display mode cycles through different options. The UART output changes to match the currently selected mode on the LCD.

Note: The accelerometer and gyroscope values show significant variation because they are raw, unfiltered data directly from the MPU6050 registers. No smoothing or sensor fusion algorithms have been applied, which is why you see the natural noise and sensitivity of the sensors.

Project Overview

This project demonstrates complete bare-metal programming on the STM32F103C8 "Blue Pill" by building a multi-sensor data acquisition system. It reads data from DHT11 (temperature/humidity) and MPU6050 (accelerometer/gyroscope) sensors, displays them on a 16x2 I2C LCD, and outputs data via UART for PC monitoring. The system runs on a precise 10ms control loop that schedules all tasks at different frequencies.

Hardware Components

Component	Description
STM32F103C8T6	"Blue Pill" development board
DHT11 Sensor	Temperature & Humidity sensor
MPU6050 Sensor	6-axis inertial measurement unit
LCD 16x2 with I2C	Character display module
USB-to-Serial Converter	CP2102 / CH340 / FTDI
Push Button	Two Leg Tactile switch

Task Scheduling

The system uses a 10ms timer-based control loop with independent counters for each task. TIMER3 is configured to drive the main control loop.

Task	Frequency	Period	Execution
DHT11 Read	1 Hz	1 second	Every 100 loops
MPU6050 Read	20 Hz	50 ms	Every 5 loops
LCD Update	10 Hz	100 ms	Every 10 loops
UART Output	10 Hz	100 ms	Every 10 loops
Button Check	Event-driven	On interrupt	EXTI + TIM4 debounce

Display Modes

The system features three display modes that can be cycled by pressing the button:

Mode	Display Content	UART Output
Mode 0 (Default)	Temperature & Humidity	Temperature and humidity data
Mode 1	Accelerometer (X, Y, Z)	Accelerometer values
Mode 2	Gyroscope (X, Y, Z)	Gyroscope values

Behavior:

• On startup, the LCD shows temperature and humidity (Mode 0)
• UART continuously outputs temperature and humidity data in Mode 0
• First button press → LCD switches to accelerometer data (Mode 1)
• Second button press → LCD switches to gyroscope data (Mode 2)
• Third button press → Returns to temperature and humidity (Mode 0)
• UART output always matches whatever mode is currently displayed

Timer Configuration

Timer	Resolution	Purpose
TIMER1	1µs	DHT11 precise timing
TIMER2	0.1ms	General delays
TIMER3	0.1ms	Control loop scheduler (10ms base)
TIMER4	0.1ms	Button debouncing (50ms)

🔗 View TIMER1 Initialization Source Code
🔗 View TIMER2 Initialization Source Code
🔗 View TIMER3 Initialization Source Code
🔗 View External Interrupt Button and TIMER4 Initialization Source Code

Pin Configuration

Peripheral	Pin	Connection	Notes
DHT11	PB0	DATA	Built-in 1kΩ pull-up
	5V	VCC	Power
	GND	GND	Common ground
MPU6050	PB8	SCL	I2C clock
	PB9	SDA	I2C data
	5V	VCC	Power
	GND	GND	Common ground
LCD 16x2 I2C	PB8	SCL	Shares I2C bus with MPU6050
	PB9	SDA	Shares I2C bus with MPU6050
	5V	VCC	Power
	GND	GND	Common ground
UART	PA9	TX to USB-Serial RX	115200 baud
	PA10	RX to USB-Serial TX	Optional for commands
Button	PA0	Mode select	Pull-up, falling edge trigger

The LCD display and MPU6050 share the same I2C bus (PB8/SCL, PB9/SDA) with different addresses:

Device	I2C Address (7-bit)	8-bit Write	8-bit Read
MPU6050	0x68	0xD0	0xD1
LCD Module	0x27	0x4E	0x4F

🔗 View Custom Written I2C Driver Source Code
Note: The LCD module uses a PCF8574 I2C backpack.

Project Schematic

Schematic designed using EasyEDA

The schematic shows the STM32F103C8T6 implementation including:

• 8MHz HSE clock circuit (for 72MHz operation)
• DHT11 sensor connection (PB0)
• MPU6050 sensor connection (PB8/PB9 I2C bus)
• LCD 16x2 I2C connection (PB8/PB9 I2C bus)
• UART interface (PA9/PA10 for USB-to-Serial)
• Push button (PA0 for mode selection)

MPU-6050 IMU Driver

The MPU6050 is a 6-axis inertial measurement unit that combines a 3-axis accelerometer and a 3-axis gyroscope.

Key Features

Parameter	Value
Interface	I2C (shared bus with LCD)
I2C Address	0x68 (7-bit)
Accelerometer Range	±2g/±4g/±8g/±16g (configurable)
Gyroscope Range	±250/±500/±1000/±2000 °/s (configurable)
Data Output	16-bit raw values

Register Map

Register	Address	Description
WHO_AM_I	0x75	Returns 0x68 for device identification
PWR_MGMT_1	0x6B	Power management and device wake-up
ACCEL_XOUT_H	0x3B	Accelerometer X-axis high byte
GYRO_XOUT_H	0x43	Gyroscope X-axis high byte
TEMP_OUT_H	0x41	Temperature sensor high byte

Implementation Details

• Burst read of all 14 data bytes in a single I2C transaction
• Data stored in global structure for access by other tasks
• Configurable measurement ranges via register writes
• Raw 16-bit values accessible for further processing

🔗 View MPU6050 Driver Source Code

Note: The data received from the MPU6050 is raw and has not been processed or filtered. No sensor fusion algorithms (complementary/Kalman filters) are applied. The accelerometer and gyroscope values are provided directly as read from the sensor registers.

DHT11 Sensor Driver

The DHT11 uses a single-wire protocol with precise timing:

Phase	Duration	Description
Start Signal	18ms LOW + 20µs HIGH	MCU wakes sensor
Sensor Response	80µs LOW + 80µs HIGH	Sensor acknowledges
Bit "0"	50µs LOW + 26-28µs HIGH	Logic 0
Bit "1"	50µs LOW + 70µs HIGH	Logic 1
Data Frame	40 bits	5 bytes (humidity ×2 + temp ×2 + checksum)

Instead of measuring pulse width, I used a simpler approach looking at datasheet:

For each bit:

1. Wait for line to go HIGH
2. Delay exactly 40µs
3. If line still HIGH → logic 1
   If line is LOW → logic 0

To ensure the timing is not interrupted, interrupts are disabled while communicating with the sensor. The checksum provided by the sensor is used to verify data integrity.

🔗 View DHT11 Driver Source Code

Lightweight String Formatting

Instead of using sprintf() (which is computationally heavy and increases code size), I created custom lightweight functions:

General Utility Functions

Function	Purpose
itoa_16()	Converts 16-bit integers to strings
itoa_8()	Converts 8-bit integers to strings
format_value()	Formats temperature/humidity with 1 decimal place

UART Output Formatting Functions

Function	Purpose	Output Example
format_reading()	Builds complete temperature/humidity line	Temp: 24.5C, Hum: 45.0%
format_accel()	Formats accelerometer data for UART	AX:123 AY:456 AZ:789
format_gyro()	Formats gyroscope data for UART	GX:12 GY:34 GZ:56

LCD Display Functions

Function	Purpose	Display Example
LCD_DisplayReading()	Shows temperature & humidity on LCD	Line1: TEMP: 24.5 C Line2: HUMD: 45.0 %
LCD_DisplayAccel()	Shows accelerometer data on LCD	Line1: AX:123 AY:456 Line2: AZ:789
LCD_DisplayGyro()	Shows gyroscope data on LCD	Line1: GX:123 GY:456 Line2: GZ:789

🔗 View Custom String Format Utility Source Code
🔗 View LCD Driver Source Code

Note: Future versions of this project will implement standardized data output protocols such as NMEA.

Getting Started

Prerequisites

Component	Details
MCU	STM32F103C8T6 "Blue Pill" board
Sensors	DHT11 (temperature/humidity) + MPU6050 (accelerometer/gyroscope)
Display	16x2 LCD with I2C backpack (PCF8574)
Communication	USB-to-Serial converter (CP2102/CH340/FTDI)
Programmer	ST-Link V2
IDE	STM32CubeIDE v1.13.0+

Installation

1. Clone the repository

git clone https://github.com/rubin-khadka/STM32_DHT11_MPU6050_LCD.git

2. Open in STM32CubeIDE

   • File → Import...
   • General → Existing Projects into Workspace → Next
   • Select the project directory
   • Click Finish

3. Verify Project Settings

   • Project → Properties → C/C++ Build → Settings
   • MCU GCC Compiler → Preprocessor
   • Ensure STM32F103xB is defined
   • MCU GCC Compiler → Include paths Add the following paths
     • "~\STM32Cube_FW_F1_V1.8.0\Drivers\CMSIS\Core\Include"
     • "~\STM32Cube_FW_F1_V1.8.0\Drivers\CMSIS\Device\ST\STM32F1xx\Include"

4. Build & Flash

   • Build: Ctrl+B
   • Debug: F11
   • Run: F8 (Resume)

Related Projects

• STM32_DHT11_UART_BareMetal
• STM32_DHT11_LCD16x2

Resources

• STM32F103 Datasheet
• STM32F103 Reference Manual
• DHT11 Sensor Datasheet
• MPU6050 Sensor Datasheet
• PCF8574 I2C Backpack Datasheet

Project Status

• Status: Complete
• Version: v1.0
• Last Updated: February 2026

Contact

Rubin Khadka Chhetri
📧 rubinkhadka84@gmail.com
🐙 GitHub: https://github.com/rubin-khadka