[sdiy] Percussion MIDI controller

[Ingo Debus]

Hi all,

Someone asked me about a pecussion MIDI controller like this: a 1...1.5 
metres (4 or 5 feet) long rod to be played with sticks/mallets. It 
should sense both the impact and the position where the stick hit it.

My first idea was attaching two piezos to the rod, one at each end, and 
sensing the time difference. So I did this and watched the outputs of 
the piezos on a dual trace scope. With wooden rod and sticks, the slope 
is way longer than the time difference itself (the speed of sound in 
solid materials is much higher than in air), and couldn't be seen on 
the scpoe at all. It's probably difficult to measure the time 
difference precisely.
Then I tried a steel rod and hit it with another piece of steel. Now 
the time difference became visible, because of the much steeper slopes. 
But hitting steel with steel makes a lot of noise in itself, so this is 
probably not very well suited for something controlling a synth.

Another idea is attaching a resistive wire to the rod and hitting it 
with an electrically conductive stick, thus sensing the position. This 
would of course require a cable at the stick. Impact would still be 
sensed with a piezo.

Anybody already done things like this?
Any other ideas?

Ingo