Mega shield

Bare Metal STM-32 Nucleo Based SmartWatch# Bare Metal STM-32 Nucleo Based SmartWatch

Project Overview## Project Overview

This project is a bare-metal implementation of a smartwatch using an AVR microcontroller (ATmega2560). The smartwatch is designed to operate at a low level, utilizing direct register manipulation and avoiding high-level abstractions. The entire project is written in C with modular architecture.This project is a bare-metal implementation of a smartwatch using the STM-32 Nucleo development board. The smartwatch is designed to operate at a low level, utilizing direct register manipulation and avoiding high-level abstractions. The project is written entirely in C.

Features## Features

• Real-Time Clock (RTC): DS3231 module for precise timekeeping with I2C interface- Real-Time Clock (RTC): DS3231 module for precise timekeeping.

• LCD Display: GC9A01 compatible 16x2 LCD via I2C- Motion Sensing: MPU6050 sensor for accelerometer and gyroscope data.

• Menu Navigation: 3-mode menu system (Time, Temperature, Stopwatch)- Heart Rate and SpO2 Monitoring: MAX30102 sensor for health monitoring.

• Stopwatch Functionality: Start/Pause and Reset operations with centisecond precision- Environmental Sensing: BME280 sensor for temperature, humidity, and pressure measurements.

• Temperature Monitoring: Real-time temperature reading from DS3231 sensor- Battery Management: TP4056 module for battery charging and monitoring.

• Button Control: Three interrupt-driven buttons for navigation and control- Display: GC9A01 round LCD for user interface.

• Timer-Based Scheduling: TIMER1 for precise timing and interrupt handling

Development Approach

Hardware Components- Bare-Metal Programming: The project is implemented without an operating system, focusing on low-level programming.

1. ATmega2560 Microcontroller: Core processor- Direct Register Access: All peripherals are controlled through direct register manipulation, ensuring maximum control and efficiency.

2. DS3231 RTC Module: Real-time clock and temperature sensor (I2C @ 0x68)- Low-Level Drivers: Custom drivers are developed for each module to interface with the STM-32 microcontroller.

3. LCD 16x2 Module: Display with I2C backpack (I2C @ 0x27)

4. Push Buttons: ## Hardware Components

   • Button NEXT (PE4, INT4): Navigate menu forward1. STM-32 Nucleo Board: The core microcontroller platform.

   • Button PREV (PE5, INT5): Navigate menu backward 2. DS3231 RTC Module: Provides accurate timekeeping.

   • Button ACTION (PD2, INT2): Start/Pause/Reset stopwatch3. MPU6050 Sensor: Measures motion and orientation.

5. MAX30102 Sensor: Monitors heart rate and SpO2 levels.

Project Structure5. BME280 Sensor: Captures environmental data such as temperature, humidity, and pressure.

smartwatch/7. **GC9A01 LCD**: Displays smartwatch data and user interface.

├── Core/

│   ├── Inc/                    # Header files## Goals

│   │   ├── main.h              # Main application header- Develop a fully functional smartwatch with essential features.

│   │   ├── i2c.h               # I2C/TWI interface- Implement all functionalities using bare-metal programming techniques.

│   │   ├── buttons.h           # Button handling- Optimize performance and power consumption through efficient low-level coding.

│   │   ├── timer.h             # Timer interrupt handling

│   │   └── stopwatch.h         # Stopwatch interface## Future Enhancements

│   └── Src/                    # Source files- Add additional sensors or modules for extended functionality.

│       ├── main.c              # Main application logic- Implement power-saving modes to extend battery life.

│       ├── i2c.c               # I2C driver implementation- Enhance the user interface with advanced graphics.

│       ├── buttons.c           # Button ISR and handling

Development Approach

• Bare-Metal Programming: No OS, direct hardware register access
• Direct Register Manipulation: Full control over microcontroller peripherals
• Modular Architecture: Separated concerns for easy maintenance and extension
• ISR-Driven: Interrupt Service Routines for button inputs and timing
• I2C Communication: Two-wire interface for RTC and LCD modules

Functional Modes

Mode 1: TIME Display

• Shows current time from DS3231 RTC
• Format: HH:MM:SS
• Hold PREV button (>1s) to reset clock to 00:00:00

Mode 2: TEMPERATURE Display

• Shows current temperature from DS3231 sensor
• Format: XX.XX°C (with 0.25°C precision)

Mode 3: STOPWATCH

• Start/Pause: Short press of ACTION button
• Reset: Long press (>1s) of ACTION button
• Format: MM:SS:CS (minutes:seconds:centiseconds)

Building the Project

Prerequisites

• ARM GCC compiler for AVR (avr-gcc)
• avrdude for flashing
• Make (optional, for automated builds)

Compilation

avr-gcc -mmcu=atmega2560 -DF_CPU=16000000UL -O2 \
  Core/Src/*.c Drivers/Custom/Src/*.c \
  -o smartwatch.elf

avr-objcopy -O ihex smartwatch.elf smartwatch.hex

Flashing

avrdude -p m2560 -c stk500v2 -P COM3 -b 115200 -U flash:w:smartwatch.hex:i

Pin Configuration

I2C Configuration

• Speed: 100 kHz (TWBR = 72)
• Devices:
  • DS3231 RTC: Address 0x68
  • LCD Module: Address 0x27

Timer Configuration

• Timer1: 16-bit CTC mode
• Prescaler: 256 (CS12 = 1)
• Compare Register: 624 (generates 10ms interrupt at 16MHz)
• Frequency: 100 Hz system ticks

Interrupt Service Routines

1. INT4_vect: NEXT button handler
2. INT5_vect: PREV button handler
3. INT2_vect: ACTION button handler
4. TIMER1_COMPA_vect: Timer compare interrupt for timing

Key Features Implementation

Debouncing

• 50ms software debounce on button presses
• Prevents false triggers from mechanical contact bounce

Time Management

• System ticks every 10ms (from TIMER1)
• Stopwatch counts in 10ms increments
• Button press timing for long-press detection

I2C Communication

• Blocking I2C transfers (appropriate for low-speed communication)
• Standard START/STOP conditions
• ACK/NACK handling for multi-byte reads

Future Enhancements

• Add additional sensors (accelerometer MPU6050, heart rate MAX30102)
• Implement BME280 environmental sensor
• Add TP4056 battery charging management
• Power management and sleep modes
• More sophisticated menu system with settings
• Data logging capabilities

Troubleshooting

LCD Not Displaying

1. Check I2C address (0x27) with I2C scanner
2. Verify pull-up resistors on SDA/SCL lines
3. Check contrast adjustment on LCD module

RTC Time Not Updating

1. Verify DS3231 I2C address (0x68)
2. Check if coin cell battery is installed
3. Ensure I2C communication is working

Buttons Not Responding

1. Check pin configuration matches header defines
2. Verify pull-up resistors are present
3. Test with multimeter for continuity

License

This project is open-source and available under the MIT License.

Author

devcristi - Embedded Systems Development

References

• AVR ATmega2560 Datasheet
• DS3231 RTC Datasheet
• I2C/TWI Communication Protocol