drums and piezo sensors

[John Speth]

Once I adapted the same flat disc type piezo buzzer as a drum trigger.  I found that the interface circuitry was easy.  If my memory serves me well, I just half wave rectified the output and limited it with a zener before driving a CD4069 inverter with a feedback cap so it would function as a one shot.  Th hardest part was soldering the wires to the disc and making a nice silicone envelope around it so the wires wouldn't pull out.  I taped the "button with a pigtail" to my buddy's tom-toms on his drum set they worked very well.

With a little extra circuitry, you can get amplitude info.

John Speth
Object Engineering, Inc.
mailto:johns at oei.com

-----Original Message-----
From:	Martin Czech [SMTP:martin.czech at intermetall.de]
Sent:	Thursday, June 25, 1998 8:38 AM
To:	synth-diy at mailhost.bpa.nl
Subject:	drums and piezo sensors

Someone wrote a nice mail about margarine containers as
diy-electro-drum trigger, and someone came up with the idea to use
rubber pads instead (mouse pads). Now, beeing in the little local
electronics shop, I saw a piezo sound transducer, a little black disk
with an opening on one side. I tryed it today with a sampling scope,
you can easily get voltages > 10V out of it. If you hit it with soft
material (rubber screw driver handle) the amplitude is low, but if you
hit it hard with a piece of metal... I think this is because the
resonant frequency of the piezo disk inside is about 2 kHz and it takes
a hard punch on the piezo plastic encapsulation to get sufficient
energy into this frequency band. This could help to separate different
sensors mounted on the same piece of wood etc. If they are damped with
rubber no "body" waves from the wood should have the necessary energy
in this frequency band, so crosstalk could be minimised. But the
plastic containment is still 4 mm thick, too much to simply mount it
between two mouse pads and the like. But beside this type of
soundtransducer I found the naked piezo element, looking like a very
thin (0.7mm) brass disk, about 4 cm diameter. One side is shiny brass,
on the other there is the silver electrodes, one can solder two wires
to them (not too hot, max 290C!). This piezo is even cheaper ($0.5) and
gives also a lot of amplitude. Maybe it is necessary to add some diode
clamping in order to protect the trigger inputs. However, these flat
piezos seem to be quite usefull as a trigger device.

m.c.

------------------------------------------------------------------------
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