Piedroit

Turn a Raspberry Pi into a footswitch that emulates a USB keyboard.

Instructions

Based on Composite USB Gadgets on the Raspberry Pi Zero from iSticktoit.net

Tested on a Rasperry Pi Zero W Rev 1.1.

Step 1: Kernel modules

To make this work, we need to enable something called a device tree overlay, and then add two modules to /etc/modules:

echo "dtoverlay=dwc2" | sudo tee -a /boot/config.txt
echo "dwc2" | sudo tee -a /etc/modules
sudo echo "libcomposite" | sudo tee -a /etc/modules

(Check out this Stack Exchange post if you want to understand what's really going on here. It's a bit gnarly.)

Step 2: Config Stuff

Create a file /usr/bin/piedroit_usb with the following content:

#!/bin/bash
cd /sys/kernel/config/usb_gadget/
mkdir -p piedroit
cd piedroit
echo 0x1d6b > idVendor # Linux Foundation
echo 0x0104 > idProduct # Multifunction Composite Gadget
echo 0x0100 > bcdDevice # v1.0.0
echo 0x0200 > bcdUSB # USB2
mkdir -p strings/0x409 # 0x409 is the Language ID for English - United States
echo "fedcba9876543210" > strings/0x409/serialnumber
echo "Dylan Beattie" > strings/0x409/manufacturer
echo "Piedroit USB Footswitch" > strings/0x409/product
mkdir -p configs/c.1/strings/0x409
echo "Config 1: ECM network" > configs/c.1/strings/0x409/configuration
echo 250 > configs/c.1/MaxPower


# Function definition for emulating a USB keyboard
mkdir -p functions/hid.usb0
echo 1 > functions/hid.usb0/protocol
echo 1 > functions/hid.usb0/subclass
echo 8 > functions/hid.usb0/report_length
echo -ne \\x05\\x01\\x09\\x06\\xa1\\x01\\x05\\x07\\x19\\xe0\\x29\\xe7\\x15\\x00\\x25\\x01\\x75\\x01\\x95\\x08\\x81\\x02\\x95\\x01\\x75\\x08\\x81\\x03\\x95\\x05\\x75\\x01\\x05\\x08\\x19\\x01\\x29\\x05\\x91\\x02\\x95\\x01\\x75\\x03\\x91\\x03\\x95\\x06\\x75\\x08\\x15\\x00\\x25\\x65\\x05\\x07\\x19\\x00\\x29\\x65\\x81\\x00\\xc0 > functions/hid.usb0/report_desc
ln -s functions/hid.usb0 configs/c.1/
# END function definition for emulating a USB keyboard

ls /sys/class/udc > UDC

Make that file executable:

$ chmod 700 /usr/bin/piedroit_usb

Add these lines to /etc/rc.local, near the end of the file but BEFORE the exit 0:

# Enable Piedroit USB keyboard footswitch emulator
/usr/bin/piedroit_usb

Step 3: Test it

Make sure you are running your Pi off an isolated USB power supply connected to the POWER micro-USB port. Do not connect the DATA micro USB port to anything yet
Reboot your Pi
Once it's up and running, connect the DATA micro-USB port to your host PC.
You should see Windows recognise and install a "Piedroit USB Footswitch" device.

Now run piedroit as sudo:

$ sudo python ./piedroit.py

Change focus on the host PC to a tool such as PassMark KeyboardTest.

Now connect GPIO pin 04 to GND - this should send the keystroke Ctrl-F1 to the host PC.

See the code in piedroit.py to see how it works and change which GPIO pins send which keystrokes.

Run it automatically

Add another line to /etc/rc.local, near the end of the file, AFTER the line that runs /usb/bin/piedroit_usb but BEFORE the exit 0:

# Start Piedroit USB keyboard footswitch emulator automatically
sudo python /home/pi/piedroit/piedroit.py &

Note the & at the end - this makes piedroit run in the background when the system boots.

btafoya / piedroit