OceanPad

OceanPad is a hardware modification project for the Logitech F710 gamepad. The original controller uses a "sandwich" PCB architecture featuring an nRF24LE1 MCU/transceiver. This project replaces that board entirely, transforming the classic F710 into a modern, low-latency Bluetooth Low Energy (BLE) gamepad with integrated motion controls.

Modes of operaton

The original F710 features a physical D ⇔ X toggle switch, originally used to swap between DirectInput and XInput. In this project, the switch is repurposed to toggle between two distinct BLE HID modes:

• X Position: The controller impersonates an Xbox Series Controller.
• D Position: The controller mimics an 8BitDo Ultimate 2 Wireless. This controller is specifically chosen because it is the only BLE controller with native motion controls support recognized by Steam Input.

Hardware

The board integrates the following key components:

• Raytac MDBT42Q-512KV2 module. A high-performance module powered by the Nordic nRF52832 (ARM Cortex-M4F).
• TDK InvenSence ICM-42688-PC. A high-precision 6-axis MEMS IMU enabling gyro aiming and motion gestures.
• PI4IOE5V6416ZDEX. A 16-port I2C GPIO expander. The expander was necessary due to the limited GPIO count on the nRF52832. Should've used nRF52840.

Software

The firmware is written in C++ targeting the Zephyr RTOS. I am currently working on extracting the HID logic into a standalone library to simplify the creation of custom HID devices for the community.

Known limitations

• BLE Privacy/IRK: If the host computer uses BLE Privacy with Identity Resolving Keys (IRK), the controller cannot maintain active pairings for both modes (X and D) simultaneously. If paired in one mode the bond in another mode will be erased. This is a documented limitation within the current Zephyr stack. I am investigating a workaround to handle dual-identity pairing more gracefully.

Using the controller

Power and Connectivity

The controller generally acts like Xbox Series Controller.

• Power On: Press the HOME button (central Logitech button). The controller will power up and attempt to auto-reconnect to the last paired host.
• Power Off: Hold the HOME button for 3 seconds.
• Pairing Mode: Hold the MODE button until the LED blinks rapidly.
  • If no pairing information exists, the controller enters pairing mode automatically upon power-up.
  • In X mode, it appears as Xbox Wireless Controller.
  • In D mode, it appears as OceanPad (mimicking 8BitDo Ultimate 2 Wireless).

LED Status Indicators

• Rapid Blinking: Pairing mode active.
• Double Flash: Waiting for a previously paired host to reconnect.
• Solid Light: Connected and active.
• Triple Flash: Axes calibration in process.
• Single Flash (Ramping Up): Gyro recalibration in process.

Special Functions & Maintenance

• Hold MODE + B: Axes calibration. Enters calibration mode (see below).
• Hold MODE + Y: Clear paired host. Erases the bonded host for the current mode (X or D).
• Hold HOME + X: Recalibrate gyro. (D-Mode only) Gyro is calibrated automatically on startup. If it's off it's possible to recalibrate it when powered. Place the controller on a flat, stable surface. The LED will flash during the process and return to solid when finished.

Stick & Trigger Calibration Procedure

If you notice drifting or truncated input ranges, perform a manual calibration:

1. Hold MODE + B for 3 seconds until the LED flashes in series of three.
2. The current position of the sticks and triggers is now set as the Deadzone/Zero point.
3. Slowly rotate both analog sticks to their full extent and depress both triggers fully.
4. To Save: Press HOME.
5. To Cancel: Press BACK to exit without saving changes.

VIBRATION button

The original VIBRATION button is repurposed:

• X Mode: Mapped to the Share/Capture button.
• D Mode: Mapped to PR (the Right Back Paddle of original 8BitDo Ultimate 2 Wireless).

Hardware building

Board acquisition

I designed the board using EasyEDA. That's the last project I used this service for since I'm switching to KiCad. In the doc directory, you'll find the Gerber, BOM, and placement files to order production from any PCB fabrication site.

• Note: I have 4 spare boards left without the module soldered. If you're ever in Belgrade and want one, feel free to DM me.

Modifying the controller

1. Disassembly: Remove batteries, unscrew, and remove the bottom case of a working Logitech F710.
2. Desoldering: Unsolder the motor (black/white) and bumper (white) wires. Unscrew the two white screws and remove the motherboard. Unscrew the left trigger assembly and unsolder it from the original board.
3. Sandwich Removal: Use a hot air gun and flux to carefully heat the original sandwich PCB edges and remove it.
4. Soldering the Mod: Solder the OceanPad board in place.
   • Correction: I initially thought the pin pitch was 1.27mm, but it is actually 1.25mm. They are slightly misaligned but functional.
5. Debug Wiring: Solder GND, Vref, SWDIO, SWCLK, and Reset to the board (add TX/RX if you need serial logs while playing with the firmware).
6. Reassembly: After flashing, unsolder the debug wires and reassemble in reverse order.

Building and flashing

Preparing environpent

Create and enter an empty directory and clone the repository. Enter oceanpad, then create and enter a fresh Python virtual environment. Install pip dependencies, then initialize and update west.

mkdir zephyr-tree
cd zephyr-tree
git clone https://github.com/vodka-bears/oceanpad
cd oceanpad
python3 -m venv .venv
source .venv/bin/activate
pip install -r pip_freeze.txt
west init -l .
west update

Actual build

To compile the firmware for the OceanPad board:

west build -b oceanpad -- -DBOARD_ROOT=$PWD

Flashing

You'll need a CMSIS-DAP adapter with a Vref pin since the F710 uses 2V for logic. If you use 3.3V logic level you might fry the module. I used a cheap pink Chinese CherryDAP from AliExpress. Solder GND, Vref, SWDIO, SWCLK, and Reset to the board, power it, and run:

west flash