Implement a Pi Keyboard Jiggler using pizero-usb-hid-keyboard

rc.local

#!/usr/bin/env bash

/home/pi/pizero-usb-hid-keyboard/rpi-hid.sh
chmod 777 /dev/hidg0

/home/pi/tickle.py &

exit 0

tickle.py

#!/usr/bin/python3

import os
import select
import time

"""Suppress screen savers by periodically toggling Caps Lock

See https://davesteele.github.io/raspberrypi/2021/04/18/keyboard-jiggler/

Intended to be run on a Gadget Tools-generated device, which configurres a USB
port to run as a USB client.

This periodically sends two Caps Lock key presses, in quick succession, to the
remote host.

This requires an installed pizero-usb-hid-keyboard environment [1], which
creates a virtual keyboard USB client.

[1]: https://github.com/raspberrypisig/pizero-usb-hid-keyboard
"""

# keycodes - 
# https://github.com/raspberrypisig/pizero-usb-hid-keyboard/blob/master/hid-gadget-test.c#L32
KEYCODE = 0x39
GDEV = "/dev/hidg0"
DELAYSECS = 55


def capstoggle():
    """Send two Caps Lock key presses in quick succession."""

    press = bytearray([0, 0, KEYCODE, 0, 0, 0, 0, 0])
    release = bytearray([0, 0, 0, 0, 0, 0, 0, 0])

    fd = None

    try:
        fd = os.open(GDEV, os.O_RDWR)
        for _ in range(2):
            for msg in (press, release):
                os.write(fd, msg)
    except Exception:
        print("Error writing device")
    finally:
        if fd is not None:
            os.close(fd)


def main():
    while True:
        capstoggle()
        time.sleep(DELAYSECS)


if __name__ == "__main__":
    main()

Hi @davesteele thanks for this and the helpful blog here . All the instructions were very clear and easy to follow.

I have a M1 Mac. The h key was definitely sent to the host computer, but I couldn't get your double caps lock press to be recognised. When connecting the Pi Zero to the Mac for the first time, the Mac offered me the keyboard set up interface, asking for a key press to confirm that the accessory is a keyboard. Just wondered if you or anyone have found a way around that?

Maybe you could modify the code to send a space at startup.