The Peasant is building a solid state percussion synthesizer, and these trigger pads will be used for the inputs. The idea behind these was to build them as inexpensively as possible, using common items for construction. These were built without spending any money at all, just using salvage parts and common household items!
The trigger pads
These are built using margarine containers. Different sizes were used just for visual effect.
The margarine containers were mounted to a wooden plate, with foam in between to minimise crosstalk. Foam was also placed inside the bottom of the containers. A BNC jack was mounted on the side of the container and wired to a piezo disk inside. Fairly thick wires and a good solid connector were used here because of vibration. Please note that only the two wire piezos work well here, the ones with a third element pick up cross talk from the other tom toms much more easily. The lid of the container has a metal plate glued on top to give more realistic "action" , and then a 1/4 inch thick hard rubber pad is glued on top of that. Although they do not completely duplicate the action of a real drum head, they are still quite playable, although they probably wouldn't stand up to heavy professional use. And all the parts for these are available for free with a little scrounging around. For example, piezo discs are commonly used in portable stereos as tweeters, just find an old broken stereo and salvage the piezos!