Indeed, the hammer made a very satisfying smack :)
In terms of detecting the jumps, I really lucked out with the trampolines. I found four exercise trampolines that included a trigger mechanism. For exercising, they were used to count your jumps and tell you a bit about your calories burned and workout times. From the pictures on the outside of the trampoline box, I wasn’t sure how hard it would be to use the included trigger. It turns out it was a simple hardware switch. The mechanics were brilliant. It used an arm touching the bottom of the tramp. When the arm moved down, it caused a momentary connection between the two contacts. Simple and reliable. The switch contacts were already terminated to an 3.5 mm audio plug. This made it even easier to connect into my system. Besides a slight change in the debounce, the button functions in the code required no change.