5.2 KiB
Pico BLE HID
This project uses a Raspberry Pi Pico W as a Bluetooth Low Energy adapter for a wired USB HID input peripheral, allowing it to connect to a host device over BLE using HID over GATT Profile.
Setup
Hardware
You will need the following hardware to make the device:
- Raspberry Pi Pico W
- USB extension cable
You will need to cut the USB extension in half and connect the wires from the female end to the Raspberry Pi Pico W. The default configuration is to attach the USB's green wire to pin 1/GP0 and USB's white wire to pin 2/GP1. You will also need to connect the red to 5V VBUS/VSYS (since you'll be powering from the USB connection, VBUS should be fine) and the black to any ground pin. Pin 38 is the closest and most convenient, or the ground test point TP1 on the back will also work. While you can connect the Raspberry Pi Pico to the host device using the micro USB port and a micro USB cable, since you have already sacrificed half of the USB extension cable, you might as well use the male half to create a standard USB-A connection. If you wish to do so, then simply connect the red and black wires of the male connector end to VBUS (5V) and GND, respectively. For the data wires, you can solder them to the two test points TP2 and TP3 on the back of the Raspberry Pi Pico. The white cable goes to TP2 and the green cable to TP3.
The individual wires on the USB can be fragile, so hot glue or other strain relief is a good idea.
Software
Download the ble_hid.uf2 file from the latest release and flash onto the Raspberry Pi Pico W by holding down the BOOTSEL button while plugging into your computer so that it appears as a USB drive, then transfer the firmware file onto the Pico W. After unmounting, the firmware install is complete.
Usage
Connect the Raspberry Pi Pico W into any USB power source (a good, small power bank will work), then plug in the desired peripheral into the female USB socket. After about a second, the onboard LED will light up, indicating it is ready to be paired over Bluetooth LE.
From the host machine, go to your Bluetooth settings and pair with the "Pico BLE HID" device. The LED should turn off when pairing begins, and it will turn back on when pairing is complete and the Raspberry Pi Pico W is ready to receive inputs. This will take a few seconds, so be patient. Once the light is back on, your device should work over the Bluetooth connection. When connecting a power-hungry device such as a gaming keyboard with many LEDs, the sudden power draw when plugging in can cause issues, so it is recommended to turn off the LEDs before connecting to the Raspberry Pi Pico W.
In principle, the Pico BLE HID will work with peripherals plugged into a USB hub, but compatibility will vary with the specific hardware used, including the peripherals, USB hub, and operating system. This is because the HID report descriptors for all interfaces on all devices are combined into a single descriptor, which has a limitation of 512 bytes. Additionally, some OSes may get confused with combinations of report descriptors that seemingly conflict. This is particularly true with modern gaming peripherals which will present as multiple interfaces of different types (e.g. a keyboard may present as a combined keyboard, mouse, joystick, and consumer control, even if it does not use any of the features of the other peripheral types), which can conflict when another peripheral of one of those other types is plugged in. This also uses up precious bytes of the limited space available for HID descriptors over GATT. Powering multiple USB devices can also cause problems -- a powered USB hub may help, but it is largely untested.
Licensing
This software is distributed under the GNU Lesser General Public License Version 3, with the exception of the libraries in the following section.
Credits
The project uses code from the following sources:
- BTstack for code from hog_keyboard_demo.c and hog_keyboard_demo.gatt distributed under their non-commercial license and the supplemental license from Raspberry Pi
- Pico-PIO-USB for templates used from the host_hid_to_device_cdc example released under the MIT license
- Raspberry Pi Pico SDK Examples for a modified version of pico_w/bt/standalone/btstack_config_common.h distributed under the BSD-3-Clause license
- TinyUSB for templates used in tusb_config.h distributed under the MIT license