Balance Bot ATmega328P

Rust implementation of a self-balancing robot using ATmega328P (Arduino Nano) from AliExpress.

Demo Video

Hardware

Components

• ATmega328P microcontroller (Arduino Nano)
• MPU6050 gyroscope/accelerometer
• TB6612 motor driver
• 2x DC motors with encoders
• HC-SR04 ultrasonic distance sensor
• RGB LED for status indication

Pin Configuration

Pin	Function
D2	Left encoder (INT0)
D3	HC-SR04 trigger
D4	Right encoder (PCINT20)
D5	HC-SR04 echo (PCINT21)
D6, D7	Right motor direction
D8	TB6612 enable
D9	Right motor PWM
D10	Left motor PWM
D12, D13	Left motor direction
A0	Red LED
A1	Green LED
A2	Blue LED
A4, A5	I2C (MPU6050)

Features

Implemented

• Balancing: PD control for angle, PI control for speed
• Sensor fusion: Kalman filter combining gyroscope and accelerometer
• Distance sensing: HC-SR04 with interrupt-driven measurement and EMA smoothing
• Obstacle avoidance:
  • Distance < 20cm: drive backwards (Blue LED)
  • Distance 20-60cm: drive forwards (Green LED)
  • Distance > 60cm: stay stationary (Red LED)
• Fall recovery: Automatic CPU reset when robot is placed upright after falling
• Real-time plotting: Serial output compatible with matplotlib plotting script

Not Yet Implemented

• Bluetooth remote control
• PID auto-tuning

Build Instructions

Prerequisites

Option 1: Dev Container (Recommended)

If you have Docker and VS Code with the Dev Containers extension:

1. Open the project folder in VS Code
2. Click "Reopen in Container" when prompted
3. All dependencies are pre-installed

Option 2: Manual Installation

Install the following:

• Rust nightly-2024-03-22 with rust-src component
• AVR toolchain: gcc-avr, binutils-avr, avr-libc, avrdude
• ravedude: cargo install ravedude

# Install Rust toolchain
rustup toolchain install nightly-2024-03-22 --component rust-src

# On Ubuntu/Debian
sudo apt install gcc-avr binutils-avr avr-libc avrdude

# Install ravedude for flashing
cargo install ravedude

Building

Important: Only release builds work due to AVR code size constraints.

# Build the firmware
cargo build --release

# Build and flash to connected Arduino Nano
./rave flash

# Or manually with ravedude
ravedude nano -cb 57600 target/avr-atmega328p/release/balance_bot_328p.elf

Serial Console

After flashing, ravedude opens a serial console at 57600 baud. Debug output shows:

• Encoder ticks and motor PWM values
• Accelerometer and gyroscope readings
• Computed angles (raw, accelerometer-only, Kalman-filtered)
• Control outputs (angle PD, speed PI, integral)
• Distance sensor readings (raw and smoothed)
• Timing information

Real-time Plotting

To visualize sensor data in real-time:

./rave | ./scripts/plot_all.py

Requires Python 3 with matplotlib and numpy.

Tuning

Key parameters in src/control.rs:

// Angle PD control
const KP_BALANCE: f32 = 23.0;
const KD_BALANCE: f32 = 0.48;
const ANGLE_ZERO: f32 = -0.17;  // Angle offset for balance point

// Speed PI control
const KP_SPEED: f32 = 7.52;
const KI_SPEED: f32 = 12.398;

// Distance thresholds (in ControlState)
distance_close_threshold: 20,   // cm
distance_medium_threshold: 60,  // cm
speed_backward: -5.0,
speed_forward: 5.0,

Architecture

┌─────────────────────────────────────────────────────────────┐
│                      Main Loop                               │
│  - Poll distance sensor (non-blocking)                      │
│  - Update target speed based on distance                    │
│  - Debug output every 300ms                                 │
└─────────────────────────────────────────────────────────────┘
                              │
┌─────────────────────────────────────────────────────────────┐
│                   TIMER2 Interrupt (100Hz)                   │
│  - Read MPU6050 (I2C)                                       │
│  - Read encoder speeds                                      │
│  - Kalman filter update                                     │
│  - PD angle control                                         │
│  - PI speed control                                         │
│  - PWM output to motors                                     │
└─────────────────────────────────────────────────────────────┘
                              │
┌─────────────────────────────────────────────────────────────┐
│                   PCINT2 Interrupt                           │
│  - Right encoder tick counting (PD4)                        │
│  - HC-SR04 echo timing (PD5)                                │
└─────────────────────────────────────────────────────────────┘

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.