Just bought a M-audio Trigger finger; a Midi drum trigger device with 16 pressure & velocity sensitive pads… sorry ..at £139 i couldn’t resist ..and bypassed the diy urge. And yes, it works supprisigly well 
Will be shortly putting up some pictures of it up in various states of assembly & provide some information about it. Which may help some of you people out there looking to build drum triggers from scratch.
A quck note about it, the drum triggers are based around a membrane holding 16 pressure sensitive resistors. Which vary their value in accordance with the pressure applied. ..i have to admit - i was expecting piezo pickups of some sort
The resistive triggers are custom made by the company www.interlinkelectronics.com This is rather blatantly displayed on the membrane itself ! They make remote controls, interface devices & oem manifacture stuff for other companys ..check them out at the above link.
Nothing new here; just the same thing everyone will get to see…
Off with the covers.. and the main board plus membrane pad are visable.
Top section of the unit, rubber trigger pad in place.
The round domed rear side to the rubber pad give the impression that the best place to hit the trigger; is in the middle !
Top side of the rubber..
annnd.. The money shot…
Here’s the all important resistive trigger pad on closeup - with the branding clearly visable.