Step 2: Planning the trigger
Some similar projects trigger a sensor with the beater itself - either with an embedded magnet or piezoelectric sensor. But this requires you to built a pad for your beater to hit (or convert a bass practice pad). This has a couple disadvantages. For one, to use the pedal with a real kit, you have to disassemble this pad, and add it again to play the video game. Also, if you're building the pad, you need to make something sturdy enough to take a lot of abuse without losing its alignment.
I decided it was much simpler all around to mount the trigger under the pedal (similar to the Rock Band design).