Homemade Teensyduino pedal works well with Loopy
I built a six-button stomp pedal with the $16 Teensy USB Development Board
Via Teensyduino the board can act as either a USB keyboard or as a USB MIDI device. I wired six momentary push buttons similar to these
to the binary inputs and adapted the USB keyboard and USB MIDI example sketches (source could be made available if there is interest).
For the pedal I installed aluminum tread plate over plywood and used scrap wood for the ends, poorly-lit cell phone photos attached.
When connecting to iPad/iPhone as a USB keyboard, a dialog saying the USB device is not supported is shown, but it works fine regardless. Go to the Key Mapping configuration in Loopy and map button presses to Loopy actions.
Connecting to iPad/iPhone as a USB MIDI device also works well, go to the MIDI Key Mapping configuration in Loopy.