[sdiy] paralleling piezos

[Harry Bissell]

There are several reasons to avoid piezos as impact sensors.

One is that it is very hard to reduce crosstalk between sensors. I made a controller
that had three rubber pads (Gladstone pads) with sensors triggering an Alesis D4, with
a fourth sensor on the body to try and reduce crosstalk (subtract body vibration). It worked
acceptably well (at least until the drummer got too drunk... :^)

Two is that the piezos have an AC response to a hit, they give a major pulse of one polarity
when hit, and one almost as big when they are released. This can cause a different kind of
false triggering. I try to diminish this by rectifying the output pulse with a shottkey
diode, The positive puse goes through a series diode, the negative is shunted by a parallel
diode. Sensitivity is reduced for soft hits (maybe a good thing as well)

FSRs are MUCH BETTER.  Interlink used to make a smaple kit that had some useful size sensors, or you
might buy a replacement KAT sensor from alternative mode.

I'm sad to hear that their sensors go bad, I didn't know that and my DrumKat hasn't been played in a LONG
time... shizzle !

H^) harry




----- Original Message -----
From: Ingo Debus <igg.debus at t-online.de>
To: sdiy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Wed, 09 Feb 2011 16:07:17 -0500 (EST)
Subject: Re: [sdiy] paralleling piezos


Am 08.02.2011 um 03:21 schrieb Alwyn Lloyd:

> The Akai MPC Series use Force Sensitive Resistors, as do the  
> DrumKAT drum pads..

I always wondered why? Piezos are much cheaper than FSRs (at least  
when bought in small quantities). Also, FSRs obviously don't last  
forever. According to alternatemode, the sensors regularly have to be  
replaced (<http://www.alternatemode.com/help/questions.php? 
questionid=7>).

I once had the chance to play a MalletKat, it's a very fine  
instrument indeed.

Ingo
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-- 
Harry Bissell & Nora Abdullah 4eva