Hwmayer documented his DIY MIDI hi-hat controller from unused bass drum pedal:
Recently one of my friends bought an electronic drum set made by polish manufacturer “DIG DRUM”. The drum set is very good and combined with the Alesis triggerIO works really well.
Unfortunately the pedal for controlling the hi-hat open/close signal was not included in the set. After a quick search, I’ve discovered that the circuit for the controller is trivial, so I decided to build my own.