Triggered wave generator/piezo questions

[Matthew Helt]

Piezo's are really fragile, trying to get them to withstand the abuse of
drummer is tricky, but there's an easy (and low-tech) way to do it.

Take a coffee can and cut out the bottom. glue the piezo to the bottom
of the metal disc (i've found hot glue works best). add a little glue
around the wire joints to ensure the connection wont come lose. you can
then mount this directly under a drum head (with a little foam it's the
perfect trigger) or stuff it in a practice pad. 

I've also tried things like adding multiple peizos to pads to trigger
differnt sources with the same pad, but this doesnt work very well as
they are hard to isolate. using more then one pizeo also helps to make
sure that the pad triggers even if you hit off center. This helped a lot
when i couldnt get a finicky alesis dm4 to trigger correctly.

For live performance situations (with a noisecore band i was in) i have
my drums triggered (multi outputs, each piezo sends output to a drum
machine, which barely works, some weird moog-like synth and a amplifier
that i can control using an effects box with my foot), then mic'd and
amplified, also affected. This all works to create a brutal and absurdly
loud drum sound that will assure audience hearing loss. On that note,
filling a drum with foam and a piezo wired disc also allows me to
practice late nights without irate neighbors... 

-matt

Q-Bot Eye wrote:
> 
> This reminds me of the drum trigger I was trying to make the other day.
> And leads me to a question I was pondering.
> 
> I was using some piezo speakers that were encased in a little metal
> jacket (disk inside jacket). I had put the speaker under the head of
> the practice pad ($1 at goodwill!). I had it right in the middle, right
> under the head, and was hitting the pad, and it was firing the seq on
> my sh-101 with the wires from the disk running directly into the ext.
> clock in-jack (no other componants inbetween). After a little abuse
> (the only time I would get a good trigger was when I would hit the head
> right where the disk was), one of the wires ripped out from the disk,
> so I ripped the metal jacket off of the disk with my teeth :), and
> soldered the wire back onto the disk. I left the jacket off, because I
> sort of had to destroy it to get it off, but now it will not work as a
> trigger. Anyone know why? It may just be something very simple, but to
> be honest, I have no idea how a piezo works, or if the metal jacket
> serves a purpose. I hooked the wires up to a jack and pluged it into an
> amplifier, and it still acted as a mic, so what is up? Could it be that
> If I had hooked up the wires from the jack backwards this time (which I
> may have, now that I think of it), would that make a difference? Would
> that send -volts?
> 
> Also, with what you guys have been saying, is it a bad idea to run the
> trigger directly into the sh-101? Could I damage it?
> 
> Thanks for putting up with my noviceness <---word?
> 
> -Andy!
> 
> --- Harry Bissell <harrybissell at prodigy.net> wrote:
> > Piezos will only go to 20V with very light loading... put a 10K on
> > them and
> > you're lucky to get 5V.
> >
> > This reminds me of my first "drum trigger" circuit... I put a piezo
> > double
> > sticky taped to the inside of a practice pad drum head... I tested it
> > and
> > it worked... so I got my (then) drummer, Steve... to test it.
> >
> > I said "go ahead - break it!"   He did with exactly one hit.  Never
> > underestimate the force of a Drummer !!!
> >
> > I spent the next several years trying designs that would survive such
> > abuse. The best was with a piece of piezoelectric film that was
> > intended as
> > a demo... it had a piezo bender about 2" long, hooked up to the leads
> > of a
> > neon bulb. The piezo generated ENOUGH VOLTAGE (in this mode) to light
> > the
> > neon at each extreme as you wiggle it back and forth...  My Bass
> > player
> > broke that... now it lives (for years) in a Kick Drum pedal.
> >
> > :^) Harry
> >
> > KA4HJH wrote:
> >
> > > >Usually piezo elements give up to 20V transients if you hit them
> > hard.
> > > >Ie. you may even need some protection network/clamp.
> > > >Depends on mechanical application.
> > >
> > > I'd say clamp it. It's not worth taking the risk of zapping your
> > > circuit. If you smack a bare transducer directly with a drum stick
> > > you could get hundreds of volts--briefly. Sort-of a loose cannon in
> > > the circuit there.
> > >
> > > Anybody done any tests? Let's have a voltage peak contest...
> > > (breaking the transducer means instant disqualification)
> > >
> > > Terry Bowman, KA4HJH
> > > "The Mac Doctor"
> > >
> > > ICQ: 45652354
> >
> >
> 
> __________________________________________________
> Do You Yahoo!?
> Bid and sell for free at http://auctions.yahoo.com

-- 
Matthew Helt (mhelt at truelink.com)
Development
http://www.truelink.com