tapping into an alesis sr16 drum machine to build electric kit

I'm trying to tap into the drum machine via the touch pads on the sr16
the problem is that i need to make a switch and nd controll velocity with a single piezo sensor .
i've tryd with a npn transistor .....it's sort of working but not triggering every time, dont think theres enough power from the piezo on lighter hits

i think i need to use a fet but i'm a bit lost with them, the circuit diagrams i've seen with them seem to be on untill a voltage is supplied to the gate but thats the opposit of what i need

dose anyone have or know any circuit diagrams that may help pleees

 

i have been working on the same project for a couple of weeks now. i am using cmos switch IC 4066 to do the same thing you are trying to achieve with transistors. The IC has four switches which close when control voltage is applied to each. Although i am still troubleshooting it as getting too much cross-talk and false triggering. Also, i am experiencing a bit of latency between hitting the homemade piezo pads and the sound coming out. Have you noticed the same problem?

 

Hi have a look at the great eDrums project;
http://www.edrum.info/pcb.html

it's mostly free open source etc how to build electronic drums, with schematics and source code. Also this page;
http://www.romanblack.com/miditemp.htm

has schematics and open source code on making simple drum controller to send MIDI messages using just one PIC chip, but is not velocity sensitive although it could be adapted to be.