mounting homebrew contact mic

[Barry L Klein]

Another approach to this could be to use coaxial cable with a kynar
insulation which has the piezo-electric properties to act as a contact
pickup of sorts.  This material is commonly used as car sensors for
traffic lights.  And I saw some of it being used as mics for violins and
basses at the NAMM show.  I just haven't tried making something up on my
own, other than a basic shock sensor hooked up to one of those in-shoe LED
circuits.

Barry

----------
From: 	CCartCat at aol.com[SMTP:CCartCat at aol.com]
Sent: 	Sunday, September 12, 1999 10:30 AM
To: 	synth-diy at mailhost.bpa.nl
Subject: 	Re:  Re: mounting homebrew contact mic

The $1.49 piezo has a deeper plastic case (I got both just in case or 
whatever).  So the wadcutter doesn't *just* protrude from the face of that

piezo (as it does when glued into the other piezo).  It's too short to 
protrude at all. 

I tried gluing one wadcutter on top of the other.  Kinda tall--protrudes
more 
(too much?).  Haven't glued the doubled wadcutter to the $1.49 piezo yet,
so 
this is all guesswork and no experience ;-) , but you might try the
doubled 
wadcutter.  Use the putty/blue goo/beeswax/adhesive to both hold the piezo
to 
the object mic'd and to shim the difference.  Or glue something solid and 
appropriately sized onto the wadcutter to extend it about an 1/8" beyond
the 
piezo case surface.  (After all, wadcutters come in a box of 250.  So you
can 
experiment with them--or take up shooting.)

And if you spring for the $1.79 piezo, you'll can build that and then
compare 
& contrast the $1.49 options to the original design.  Or do an exchange
for 
the $1.79 and remove all doubt. (I've opened the blister pack on mine, am 
curious, have approx. 240 wadcutter pellets on hand--thus, I'm committed.)

Hope this OT blather helps,
Kevin


In a message dated 9/10/99 11:58:36 PM, Harry B. wrote:

<<Hell... give it a try...

Essentially they are similar. The two wire unit is all you require... The 
three
wire unit has a little "feedback" strip that is used with a single
transistor 
to
make an oscillator (the main element (speaker) vibrates and the little
element
picks it up (mic) and the transistor amplifies it... and because the piezo
has
mass and stiffness (and is mounted at the nodes) it has a natural resonant
frequency and oscillates there...

I've used both kinds...

search for MuRata Erie (or someting like that) they manufacture all these
devices...

And it doesn't have to be a wadcurrer pellet, any small weight would do
something... experiment... BB, lead shot... solder ball... whatever.

"Hell its only money"   :^) Harry

P.S. I got the 273-064 (just went downstairs and looked....)

PPS. The pellets are Beeman H&N Match wadcutter pellets cat # 3011
(but for heavens' sake use whatever you can find....)

Christian Oncken wrote:

> Well, I went to radioshack today... I forgot to take the part# with me,
so
> after much headscratching and deliberation, I came home with a different
> model than the one described in your email.... its part# 273-073a,
'piezo
> transducer' $1.49.  it says 1500 to 3000hz...
>
> I think I did see the 273-064 part... it was $1.79 just like you said...
but
> it was labeled 'piezo buzzer' or something like that, I dont know if
there's
> a difference...
>
> Still havent got the wadcutter pellet yet...
>
> But anyway, since I got the wrong part, can you tell me if this one will
> work?  Or would you suggest taking it back for an exchange on the right
one?
>
> Any suggestions, ideas or advice you can give me would be greatly
> appreciated.  I'm new to this stuff... Any web resources for this kind
of
> thing?
>
> thanks for all your help.
>
> Christian Oncken.
>
> >Yes... airrifle pellet... very light (as pellets go) and has a flat
nose so
> it
> >is easy to glue reliably...
> >
> >The piezo as a driver will probably not have enough "balls" to drive a
> spring,
> >esp at low frequencies... I'd use a iron spring (or iron rod... pipe
etc)
> ir for
> >a small spring, a ferrite bead... and drive with an electromagnet
driven
> from a
> >stereo amp... Get enough turns so you don't fry it...
> >
> >Slinkies make good springs... if you put a magnetic pickup on a few
> stretched
> >slinkies, and then KICK it it makes a wonderful explosion...  "Yes"
(the
> band)
> >shared that idea during a soundcheck during the "Relayer" tour... used
in
> "The
> >Gates of Delirium"... Its like kicking a spring reverb but much BIGGER
!!!
> >
> >Christian Oncken wrote:
> >
>>