Some of those cheap USB foot pedal switches have a disturbingly custom software architecture. When I bought one off Amazon, it turned out to not even be HID - it needed special drivers and everything. Even the ones that are HID-compliant usually demand some custom software for initial setup ("which key do you want me to pretend to be?") that invariably only speaks windows. Which is annoying, because this really should be just a full-hardware solution that speaks USB HID and uses a set of DIP switches on the back for the desired scancode.
That was my first thought - I selected some generic USB pedal, but it failed to arrive, so I used what I had at hand. Also, there could be a problem with pre-made USB pedals - they may only transmit events on pedal down, like it happened for Vim Clutch author (https://github.com/alevchuk/vim-clutch).
