Greetings,

On Tue, 2 Mar 2004, Denny Esterline wrote:

> Hey guys and gals,
> I need some sensors to pick up vibration. Needs to be sensitive in two
> axis, and capable of detecting being bumped with less than 1/8 inch
> movement. It'll feed a PIC so I can work with most any output, but I only
> need a single pulse when it's bumped.
>
> Right now I need about a dozen, but eventually I might need several
> hundred. And yes I could do it with an accelerometer from analog, but I was
> hoping for something simpler/cheaper.
>
> Ideas?

   Back in my alarm system days, we had a sensor that was simply a small
weight attached to a thin strip of flexible metal.  The metal strip rested
on a contact, completing a Normally Closed ciruit.

   When there was vibration (i.e. pounding fist on a glass window or door,
busting through a cinderblock wall with a drill, hammer, chisle, sledge)
the contact would vibrate open.  The circuit was monitored for any brief
"opens" and would then latch the alarm.

   I believe that Radio Shack carries these devices in their stores.
Would guess that they are only a couple dollars.  BTW - The sensitivity
was adjustable with a screw that would change the tension of the metal
strip.  You can mount them in various orientations to get greater
sensitivity in each axis, though with intense vibration they may all go
off simultaniously.

   Enjoy!
      --- Jay

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