Velocity Sensitive Drum Trigger from Old Headphones

Step 4 Prep Ear-bud

Remove the plastic casing around the ear-bud, then cut a small hole in the larger section of mouse pad for the ear-bud to fit into. Make it smaller than the ear-bud so it can't slip through.
You can use a pair of broken headphones as you only need one speaker. Cut away the broken one.