Zero configuration auto-calibrating DIY head tracker

Head Tracker runs on Seeeduino XIAO BLE Sense and Arduino Nano 33 BLE boards and connects to OpenTX and ETHOS radios via either wired (PPM) or wireless (Bluetooth) trainer link.

Quick Setup

• Buy Seeeduino XIAO BLE Sense board
• Flash firmware
  • Plug-in the board to your computer
  • Double tap on RST button on the board (little one, near USB-C plug), XIAO-SENSE USB drive pops up
  • Download ht_xiao-ble_x.x.x.uf2 from latest release
  • Copy the file to XIAO-SENSE USB drive
  • USB drive disconnects itself and reboots (congrats! now you have your head tracker!)
• Connect to your radio
  • Pick up your radio with wireless trainer link (PARA, Bluetooth)
    all recent FrSky radios have wireless trainer that works; other radios may require PARA Wireless module installed
  • Connect XIAO BLE Sense board as a wireless trainer
    learn board's ID via serial console or by attaching little screen (see below) or by walking with your laptop, radio and board away from other bluetooth sources
  • Define mixers in your radio from Trainer 1,2 and 3 channels to your desired model outputs
    you may want to scale outputs to match rotation angels of the head tracker and your camera gimbal
• Attach Head Tracker to your FPV goggles
  see STL files in "case" folder, screen and button are optional
• Calibrate and Setup
  nothing to do here, skip to the next item
• HAVE FUN!
  and consider installing our own fpv camera gimbal on your favourite model!

Video Tutorials

• Connect the head tracker wirelessly to your radio
  watch full video to learn how to power the head tracker with a 1-cell lipo battery

Fully assembed

Don't feel DIY? Order the fully assembled head tracker with display and button from our shop at Etsy.

• DJI FPV V1/V2 Goggles
• Walksnail Avatar Goggles X

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Camera Gimbal

Check our DIY 3D printed Micro Camera Gimbal
Join our dedicated Facebook group

Also available now to order ready to use on Etsy

Tested radios

• FrSky X-Lite Pro (OpenTX)
• FrSky X20S Tandem (EthOS)
• Radiomaster TX16S can be modified to have wireless trainer link and work with the head tracker

Wiring reference

• D2: Orientation reset pin, use a button that connects this pin to GND
• D8: PPM mode activation pin, solder it permanently to GND or use a positional switch
• D10: PPM signal pin, connect it to an audio jack tip and GND to the jack body
• SDA&SCL: I2C communication pins, connect them to 128x32 SSD1306 screen

Supported boards

Listed boards are perfect for a head tracker project, since they have both IMU for orientation and Bluetooth for connectivity.

XIAO BLE Sense is a tiny board with UF2 bootloader and SoftDevice (bluetooth driver) pre-flashed that makes it very easy to use. The board is relatively new and may be harder to find. Please pay attention and order "Sense" variant, it has IMU.
Recommended for users w/o experience in embedded programming.

Nano 33 BLE is a larger board from Arduino that shall be easier to source. There are two variants of this board: "Nano 33 BLE" and "Nano 33 BLE Sense" -- both will work for this project. This board has no UF2 bootloader pre-flashed and a debug probe is required to flash UF2 bootloader to it.
Recommended for advanced users who have a debug probe (JLink or CMSIS-DAP compatible) and can use it.

For a long time, Nano 33 BLE was the only board supported. It has an additional sensor, magnetometer, that head trackers usually use to eliminate pan drift. In practice, however, magnetometer adds more problems than solves. Magnetometer is very sensitive to environment and tricky to calibrate properly. In this project we do not use magnetometer and have a good zero-configuration automatic continuous gyro calibration instead to solve the drift problem. Already after first 5 seconds the calibration is good enough to stop the drift.

As of now, Nano 33 BLE board does not provide any benefit over XIAO BLE Sense. Instead, the later board is actually easier to use, thanks to pre-flashed UF2 bootloader and smaller size. In the future, just for fun, magnetometer support can be added but only if we can make calibration automatic and transparent for the user.

You have another nRF52840-based board with IMU and want to use it? File a feature request. Better yet, make a PR directly!

Flash binary

XIAO BLE Sense (Simple)

Connect the board to your computer, double-tap on RST button and copy ht_xiao-ble_xxx.uf2 file to XIAO-SENSE usb drive.

Nano 33 BLE (Advanced)

First, you shall flash UF2 bootloader to the board. You only need to do this once for each new board. Then connect the board to your computer, double-tap on button and copy ht_nano-33-ble_xxx.uf2 file to NANO33BOOT usb drive.

Use head tracker

Attach the head tracker to your FPV goggles.
Power the head tracker via USB, 1 cell lipo battery or 5v source.

Hint: I personally use analog adapter bay on my DJI V1 goggles to source 5v.

Bare

The head tracker is usable "bare", no extra accessories needed, not even a button.
To reset the orientation without a button, simply double-tap the head tracker.

Hint: When the head tracker is mounted on your goggles directly, you can just double-tap your googles in any place to reset the orientation.

LEDs

On start, board shall blink continuously blue, red and green/orange leds.

• Blue led indicates Bluetooth state and blinks while not connected, it switches to solid blue upon successful connection to your radio (see below);
• Red led indicates initial gyroscope calibration, you shall wait until the red led is off before use, normally no more than several seconds;
• Green/orange led indicates health of the head tracker and shall slowly blink during normal operation.

Buttons

The head tracker records initial orientation on power up, place your goggles accordingly or reset orientation later by double-tapping the head tracker or by using a reset orientation button that can be wired to D2 and GND pins.
Keep reset orientation button pressed on power up to discard calibration parameters stored in flash memory.

Display

If you have a LED 128x32 display added you your board (via I2C), the board's bluetooth address is displayed on it. Blinking ":" symbols indicate bluetooth connection status, like blue led. Upon start, while gyroscope is calibrating, you shall see head tracker version briefly on the screen. The version is then replaced by 3 horisonal bars, one for each axis: pan, tilt and roll.

Connect to radio

HeadTracker can work either in wireless (Bluetooth) or wired (PPM) mode.
Bluetooth mode is active by default.

Bluetooth

• Flash your board with a release file
• Connect to the board with a Serial console and make note of the board address (like: 7b:f5:1e:35:de:94)
• SSD1306 LED display can be connected (via I2C) to the board; in such case board address displyed there too
• In your radio, select Trainer mode "Master/BT", wait a bit and click "[Discover]"
• Search for your board by address you noted earlier and Connect to it
• Blue led on the board shall turn on indicating successful connection
• Do not forget to configure Trainer function in your radio either on "Special Functions" screen of your model or on "Global Functions" of your radio setup.

Wire

• Activate PPM trainer output by connecting D8 and GND pins.
• Collect PPM signal from D10 pin. (Audio jack tip shall be connected to D10 and rest to GND)

Related links

• DIY-Head-Tracker
  Original DIY head tracker for Arduino Nano with separate IMU board and PPM over cable
• RC HeadTracker by Cliff
  Another version of head tracker, based on Arduino Nano 33 BLE board.
• Bluetooth Smart/BLE Crash Course
• Bluetooth low energy Characteristics, a beginner's tutorial