FPV Head Tracking Module

A wireless head tracker that converts head movements into RC radio commands for FPV flying. Pitch, roll, and yaw from your head are sent as a PPM signal to your radio's trainer port — no PC required.

📺 YouTube build video:

📺 YouTube flight test: 🖨️ 3D printable case: Thingiverse #7389266

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How It Works

Head movement → BNO085 IMU → ESP32-C3 → PPM signal → 3.5mm cable → Radio trainer port → Sim / Aircraft

The head tracker plugs into the trainer port of any EdgeTX/OpenTX radio. A switch on the radio toggles between normal stick control and head-tracker input, so you can always take over manually.

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Status

• ✅ Software emulator with 3D web interface
• ✅ PPM output via RMT hardware (jitter free)
• ✅ BNO085 real IMU firmware tested working
• ✅ Calibration button for zeroing axes
• ✅ Passive buzzer feedback (startup melody, calibration, errors, battery warnings)
• ✅ Battery voltage monitoring with low/critical beep warnings
• ✅ 3D printed case with headset mount and handheld variants — Thingiverse
• ✅ Final assembly complete
• ⏳ Field testing (see YouTube channel for updates)

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Repository Structure

headtracking-module/
├── 01-head_tracker_emulator/       # PPM emulator with WiFi + 3D web UI (test without IMU)
├── 02-bno085_wiring_test/          # Verify BNO085 wiring and axis directions
├── 03-buzzer_test/                 # Test buzzer patterns and find resonant frequency
├── 04-battery_wifi_test/           # Battery voltage monitor with web UI for calibration
├── 05-head_tracker_bno085/         # Main firmware — IMU + PPM + buzzer + battery
├── images/
│   └── wiring_diagram.svg          # Wiring schematic
├── ppm_demo.html                   # Interactive visualisation of PPM signal
├── README.md
├── WIRING.md                       # Detailed wiring guide
└── LICENSE

The sketches are numbered in the recommended build order — flash and test each one to verify each subsystem before moving to the main firmware.

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Hardware

Part	Details
ESP32-C3 SuperMini	Main controller
TENSTAR BNO085	9-axis IMU, VR/AR optimised
1S Li-ion / LiPo battery	Power (any 3.7V battery works)
TP4056 module	Battery charging via USB-C
Slider switch	Power on/off
6x6mm momentary button	IMU calibration
Passive buzzer	Audio feedback (~2kHz resonant)
2x 10kΩ resistors	Battery voltage divider
PJ-341 3.5mm TRS jack	Panel mount in case
Vention 3.5mm TRS cable 1.5m	PPM signal to radio
Perfboard 4x6cm	Switch/button mounting
Velcro straps	Goggle mounting

See WIRING.md for the complete wiring diagram and pin assignments. 3D printable case files on Thingiverse.

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Software Setup

Arduino IDE

1. Add ESP32 board URL in File → Preferences → Additional Board Manager URLs:

https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json

2. Install esp32 by Espressif Systems via Board Manager

3. Select board: ESP32C3 Dev Module

4. Set USB CDC On Boot → Enabled

5. Install libraries via Library Manager:

   • WebSockets by Markus Sattler (needed for 01-head_tracker_emulator and 04-battery_wifi_test)
   • Adafruit BNO08x (needed for BNO085 firmware)
   • Adafruit Unified Sensor (dependency)
   • Adafruit BusIO (dependency)

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Build Order (Recommended)

The numbered folders correspond to the recommended build sequence. Flash and verify each one before moving to the next:

Step	Sketch	What to verify
1	01-head_tracker_emulator	PPM output reaches radio, channels respond in EdgeTX channel monitor
2	02-bno085_wiring_test	I2C communication works, all 3 axes respond to tilt
3	03-buzzer_test	Buzzer sounds, find loudest frequency for your specific buzzer
4	04-battery_wifi_test	Calibrate voltage divider against multimeter reading
5	05-head_tracker_bno085	Main firmware with your calibrated values

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Main Firmware Usage

1. Wire all components per WIRING.md
2. Adjust calibration values in 05-head_tracker_bno085.ino:
   • DIVIDER_RATIO — from your resistor measurements
   • ADC_CORRECTION and BATT_CALIB — from battery test sketch
   • INVERT_PITCH/ROLL/YAW — from BNO085 axis test
3. Flash to ESP32-C3
4. Power on — listen for the startup melody (4 ascending notes)
5. Connect 3.5mm cable to radio trainer port
6. In EdgeTX: Model → Trainer → Master/PPM, assign enable switch
7. Put on headset, look forward, press calibration button (1 beep confirms)
8. Fly!

Beep patterns

Sound	Meaning
4 ascending notes (C-E-G-C)	Startup — board ready
1 beep	Calibration confirmed
2 spaced beeps	Battery LOW (<3.5V) — every 30s
5 fast beeps	Battery CRITICAL (<3.3V) — every 5s
1 long beep (looping)	BNO085 not found

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Emulator Usage

For testing without hardware (just ESP32 + 3.5mm cable — no IMU needed):

1. Flash 01-head_tracker_emulator.ino to ESP32
2. Connect to WiFi: HeadTracker / password: flyfpv123
3. Open browser: http://192.168.4.1
4. Drag 3D head to control axes

Web UI controls:

Input	Axis
Left drag horizontal	Yaw
Left drag vertical	Pitch
Right drag horizontal	Roll
Q / E keys	Roll left / right
Arrow keys	Pitch + Yaw
RESET CENTER button	Zero all axes

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PPM Channel Mapping

Channel	Axis	Range
CH1	Roll (lean left/right)	±45°
CH2	Pitch (nod up/down)	±45°
CH3	— center —
CH4	Yaw (turn left/right)	±90°
CH5–8	— center —

• PPM pulse width: 300µs (matches Radiomaster default)
• PPM frame: 22,500µs

See ppm_demo.html for an interactive visualisation of the PPM signal.

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Radio Setup (RadioMaster TX16S)

1. Connect 3.5mm TRS cable to trainer port on top of the radio
2. Model Settings → Trainer → Master/PPM
3. Map channels: CH1=Roll, CH2=Pitch, CH4=Yaw
4. Assign trainer enable switch (SD or SH recommended for momentary override)
5. Flip switch to activate head tracking, flip back for full stick control

Works with any EdgeTX/OpenTX radio that has a 3.5mm PPM trainer port.

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Technical Details

PPM Implementation

Uses the ESP32 RMT (Remote Control Transceiver) hardware peripheral via a dedicated FreeRTOS task — pulse timing is handled in hardware, immune to WiFi stack interruptions.

Key details:

• rmtSetEOT(PPM_PIN, 1) keeps pin HIGH between frames (prevents CH1 jitter)
• Channel values updated atomically (locals computed first, then assigned)
• Exponential smoothing on all axes

Battery Monitoring

The ESP32-C3 ADC needs some care:

• Use GPIO 0 for the battery ADC input — GPIO 2 has a hardware pullup that pollutes readings
• Firmware includes ADC_CORRECTION to compensate for ADC nonlinearity at 11dB attenuation
• The 04-battery_wifi_test sketch helps calibrate all three values (divider ratio, ADC correction, offset) via a live web interface

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Tuning

Axis inversion

In 05-head_tracker_bno085.ino, flip flags if an axis is backwards for your mount:

#define INVERT_PITCH  false
#define INVERT_ROLL   false
#define INVERT_YAW    true

Sensitivity

Adjust deflection range:

#define PITCH_RANGE   45.0f   // ±45° = full stick deflection
#define ROLL_RANGE    45.0f
#define YAW_RANGE     90.0f

Smoothing

#define SMOOTH 0.5f  // 0.1 = very smooth, 1.0 = no smoothing

Battery calibration

Determined empirically using 04-battery_wifi_test:

#define DIVIDER_RATIO  2.077f   // (R1 + R2) / R2
#define ADC_CORRECTION 0.886f   // ESP32-C3 ADC nonlinearity fix
#define BATT_CALIB     -0.13f   // fine-tune offset

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Compatible Radios

Any radio with a 3.5mm PPM trainer port and EdgeTX/OpenTX:

• RadioMaster TX16S ✅ (tested)
• RadioMaster Pocket ELRS
• RadioMaster Zorro
• RadioMaster Boxer
• Any EdgeTX/OpenTX radio with trainer port

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Credits & Links

• 📺 YouTube build video: https://youtu.be/ZS9i_QNzIO0
• 📺 YouTube flight test: coming soon
• 🎥 Channel: @flyuafpv
• 🖨️ 3D printable case: Thingiverse #7389266
• 💾 Source code: this repo

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License

MIT — see LICENSE