Wireless Head Tracking System

A real-time wireless head tracking system using ESP32 Microcontrollers that captures head orientation and replicates it mechanically using servos. This system uses dual IMU sensors for accurate 2-DOF rotational tracking (yaw and pitch) and ESP-NOW protocol for low-latency wireless communication.

Table of Contents

• Overview
• Features
• Hardware Requirements
• System Architecture
• How It Works
• Circuit Diagrams
• Installation & Setup
• Calibration
• Usage
• Troubleshooting
• Applications
• License

Overview

This project implements a wireless head tracking system consisting of two main units:

• Transmitter Unit: A wearable device with dual IMU sensors that measures head orientation
• Receiver Unit: A servo-controlled mechanism that replicates the tracked head movements

The system provides real-time tracking with approximately 100ms latency at 10Hz update rate using the ESP-NOW protocol for reliable wireless communication.

Features

• Dual IMU Sensor Fusion: Combines MPU6500 and MPU6050 sensors for accurate tracking
• Yaw Tracking: 360° continuous rotation tracking via gyroscope integration (servo output limited to 180°)
• Pitch Tracking: ±90° tilt detection using accelerometer data
• Wireless Communication: ESP-NOW protocol for low-latency data transmission
• Gyroscope Calibration: Automatic offset calibration at startup to minimize drift
• Signal Filtering: 5-sample moving average filter for smooth motion
• Data Validation: Built-in checks for unrealistic sensor readings
• Manual Reset: Serial command interface to reset yaw orientation
• Servo Control: Precise mechanical replication of head movements

Hardware Requirements

Transmitter Unit

• ESP32 Development Board
• MPU6500 (or MPU9250) - Gyroscope for yaw tracking
• MPU6050 - Accelerometer for pitch tracking
• Power source (battery recommended for wearable use)

Receiver Unit

• ESP32 Development Board
• 2× Servo Motors (180° range)
  • Yaw servo (horizontal rotation)
  • Pitch servo (vertical tilt)
• Power supply suitable for servos (5V, adequate current)

Additional

• I2C pull-up resistors (if not integrated on sensor modules)
• Connecting wires
• Mounting hardware/headset frame

System Architecture

Block Diagram

graph TD
    subgraph TX["TRANSMITTER"]
        SENSORS("MPU6500 Gyro<br/>MPU6050 Accel<br/>I2C: 0x69 & 0x68")
        PROCESS("ESP32 Processing<br/>Calibration & Filtering<br/>Yaw: Gyro 0-360°<br/>Pitch: Accel ±90°")
        SENSORS --> PROCESS
    end

    subgraph COMM["WIRELESS LINK"]
        PACKET("ESP-NOW Protocol<br/>OrientationData<br/>yaw, pitch, timestamp<br/>10Hz @ 100m range")
    end

    subgraph RX["RECEIVER"]
        RECEIVE("ESP32 Receiver<br/>Timeout Detection<br/>Exponential Smoothing")
        MAPPING("Servo Mapping<br/>Yaw: 0-180° → 180-0°<br/>Pitch: ±90° → 180-0°")
        SERVOS("Servo Control<br/>GPIO18 Yaw<br/>GPIO19 Pitch<br/>PWM: 1-2ms")
        RECEIVE --> MAPPING
        MAPPING --> SERVOS
    end

    TX --> COMM
    COMM --> RX

    style TX fill:#1a1a2e,stroke:#e94560,stroke-width:3px,color:#fff,rx:10,ry:10
    style RX fill:#1a1a2e,stroke:#0f3460,stroke-width:3px,color:#fff,rx:10,ry:10
    style COMM fill:#16213e,stroke:#53a8b6,stroke-width:3px,color:#fff,rx:10,ry:10
    style SENSORS fill:#e94560,stroke:#fff,stroke-width:2px,color:#fff
    style PROCESS fill:#e94560,stroke:#fff,stroke-width:2px,color:#fff
    style PACKET fill:#53a8b6,stroke:#fff,stroke-width:2px,color:#000
    style RECEIVE fill:#0f3460,stroke:#fff,stroke-width:2px,color:#fff
    style MAPPING fill:#0f3460,stroke:#fff,stroke-width:2px,color:#fff
    style SERVOS fill:#0f3460,stroke:#fff,stroke-width:2px,color:#fff

Loading

The system uses a master-slave architecture where the transmitter continuously broadcasts orientation data, and the receiver listens and actuates the servos accordingly.

How It Works

Transmitter Operation

1. Sensor Initialization

   • MPU6500 initialized at I2C address 0x69 (AD0 pin high)
   • MPU6050 initialized at I2C address 0x68 (AD0 pin low)
   • Both sensors share the I2C bus (SDA: GPIO21, SCL: GPIO22)

2. Gyroscope Calibration

   • Collects 500 samples while sensor is stationary
   • Calculates average offset for gyroscope Z-axis
   • Warns if offset exceeds ±10°/s (indicates unstable environment)

3. Yaw Calculation (MPU6500)

   • Reads gyroscope Z-axis angular velocity
   • Subtracts calibrated offset
   • Applies 5-sample moving average filter
   • Integrates over time: yaw += gyroZ_filtered × deltaTime
   • Normalizes to 0-360° range
   • Validates data (rejects readings > 1000°/s)

4. Pitch Calculation (MPU6050)

   • Reads 3-axis accelerometer data
   • Converts to g-forces (±2g range, 16384 LSB/g)
   • Calculates magnitude to validate data (0.5g - 1.5g expected)
   • Computes pitch: pitch = atan2(ay, sqrt(ax² + az²)) × 180/π

5. Wireless Transmission

   • Packages yaw and pitch into struct
   • Transmits via ESP-NOW to receiver MAC address
   • Updates at 10Hz (100ms interval)

Receiver Operation

1. ESP-NOW Reception

   • Listens for incoming orientation data packets
   • Validates packet size matches OrientationData struct

2. Servo Mapping

   • Yaw: Maps 0-180° input to 180-0° servo (inverted for mechanical correction)
   • Pitch: Maps -90 to +90° input to 180-0° servo
   • Constrains values to prevent servo damage

3. Servo Actuation

   • Writes mapped values to servos (GPIO18 and GPIO19)
   • Servos configured with 1000-2000μs pulse width range

Circuit Diagrams

Transmitter Circuit

Pin Connections:

• MPU6500: SDA → GPIO21, SCL → GPIO22, AD0 → VCC (address 0x69)
• MPU6050: SDA → GPIO21, SCL → GPIO22, AD0 → GND (address 0x68)

Receiver Circuit

Pin Connections:

• Yaw Servo Signal → GPIO18
• Pitch Servo Signal → GPIO19
• Servo Power: Connect to adequate 5V supply (not USB power)

Installation & Setup

1. Arduino IDE Setup

# Install Arduino IDE and add ESP32 board support
# In Arduino IDE: File → Preferences → Additional Board Manager URLs
# Add: https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json

2. Install Required Libraries

• ESP32Servo
• MPU6050 (by Electronic Cats)
• MPU9250_asukiaaa

# In Arduino IDE: Tools → Manage Libraries
# Search and install each library

3. Configure Receiver MAC Address

Before uploading transmitter code:

1. Upload the receiver code first
2. Open Serial Monitor (115200 baud)
3. Note the displayed MAC address
4. Update the MAC address in Transmitter/Transmitter.ino line 30:

uint8_t receiverAddress[] = { 0xXX, 0xXX, 0xXX, 0xXX, 0xXX, 0xXX };

4. Upload Code

1. Upload Receiver.ino to receiver ESP32
2. Upload Transmitter.ino to transmitter ESP32

Calibration

Gyroscope Calibration

The transmitter automatically calibrates on startup:

1. Place the transmitter on a stable surface
2. Keep it completely stationary
3. Power on and wait for "Calibrating gyroscope..." message
4. Calibration completes after ~2 seconds
5. Check that offset is within ±10°/s

Servo Centering

Servos automatically center at 90° during receiver initialization. Adjust mechanical mounting if needed to ensure proper range of motion.

Usage

1. Power On

   • Power the receiver unit first
   • Power the transmitter unit (triggers auto-calibration)

2. Verification

   • Open Serial Monitor on receiver (115200 baud)
   • Verify data reception: "Received -> Yaw: X | Pitch: Y"
   • Check servo movement matches head orientation

3. Reset Yaw

   • Connect to transmitter via Serial Monitor
   • Send command: reset
   • Yaw resets to 0°

4. Normal Operation

   • Wear or mount transmitter on head
   • Servos will replicate yaw and pitch movements
   • Yaw: Transmitter tracks 0-360° continuously, servo replicates 0-180° mechanically
   • Pitch range: ±90°

Troubleshooting

Sensors Not Detected

• Check I2C wiring (SDA, SCL, VCC, GND)
• Verify I2C addresses (use I2C scanner sketch)
• Ensure AD0 pins are correctly connected (high for 0x69, low for 0x68)

Gyroscope Drift

• Recalibrate in a more stable environment
• Check for vibrations or movement during calibration
• Verify gyro offset is within ±10°/s

No Data Reception

• Verify receiver MAC address in transmitter code
• Check ESP-NOW initialization messages
• Ensure both devices are powered and within range (~100m line-of-sight)

Erratic Servo Movement

• Check power supply (servos need adequate current)
• Verify servo connections to correct GPIO pins
• Ensure data validation isn't rejecting readings (check serial output)

Invalid Data Warnings

• "Gyroscope data invalid": Excessive angular velocity detected, reduce movement speed
• "Accelerometer data invalid": Magnitude check failed, sensor may be loose or malfunctioning

Applications

• Camera Gimbals: FPV systems, cinema rigs
• Robotic Heads: Interactive robots, animations
• VR/AR Tracking: Head-mounted display orientation
• Remote Camera Control: Surveillance, telepresence
• Motion Capture: Animation reference, biomechanics
• Accessibility Devices: Head-controlled interfaces
• Gaming: Immersive head-tracking peripherals

License

This project is licensed under the terms included in the LICENSE file.