Pocket link

Pocket Link

A small USB-C adapter that lets a Pocket bot hear and speak on an Android phone's own calls, and (firmware 0.2) tap and type on the phone for it. The phone sees a USB headset, so Android routes the call's audio to it; a second channel on the same plug carries that audio to the Pocket app, which streams it to the voice engine over the phone's own internet. No Bluetooth, no Wi-Fi, no battery, nothing stored on the device.

This is open hardware. The board, the firmware, the USB protocol and the test tools are here so that anyone can see exactly what the thing plugged into their phone does, build one, or make it work on a phone we have not tried.

caller ⇄ phone (cellular / WhatsApp call)
           │  Android routes call audio to the "USB headset"
           ▼
   USB-C ⇄ Pocket Link (RP2040)
           │  interface 1–2: USB Audio (UAC 1.0) headset, mic in / headphones out
           │  interface 3:   vendor bulk data channel
           │  interface 4:   HID touch screen + keyboard (firmware 0.2): the app's taps and keystrokes
           ▼
   Pocket app (USB host API) ⇄ WebSocket ⇄ voice engine

Build one (DIY)

You do not need our board. Any RP2040 board works for a first test:

1. Hold BOOT and plug a Raspberry Pi Pico or Waveshare RP2040-Zero into a PC; copy firmware/pocket-link-fw/pocket-link-fw.uf2 onto the RPI-RP2 drive.
2. Run python3 firmware/tools/link_pc_test.py status (needs pyusb numpy and the udev rule in firmware/README.md). loopback must pass both ways.
3. Connect the board to the phone with a USB-C OTG cable, install the Pocket app, open Account → Voice → Pocket Link, and set it up. The app recognises the device by its USB identity.

A Pico on an OTG cable is a working Pocket Link. It is also a lever on your phone's port; the pod in revB/ exists because of that.

Licences

• Hardware (revA/, revB/): CERN-OHL-P-2.0 (LICENSE-HARDWARE.txt). Permissive: build it, sell it, change it, keep the notice.
• Firmware, tools and the test app (firmware/): Apache-2.0 (LICENSE). third_party/usbd-audio is MIT OR Apache-2.0 by its author, with our patches listed in its PATCHES.md.
• "Pocket" and "Pocket Link" are names of Pocket; a clone of the design is welcome, a clone of the name is not.

USB identity

Rev A ships with the pid.codes test ID 1209:0001. Before a public batch we apply for a real PID at pid.codes, which allocates them to open-source hardware; PID-REQUEST.md is the application. Until then, anything you build with this firmware carries the test ID, which must not be sold.

Contributing

Phone reports (COMPATIBILITY.md), firmware fixes and alternative boards are all welcome; see CONTRIBUTING.md. Bring-up lessons so far: the headphones stream must be stereo (a mono USB output makes Android 16's mixer abort audioserver), and the app should claim the device through a USB_DEVICE_ATTACHED intent filter so Android offers "always" on the permission prompt.