>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 27 May 2005 12:24
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE]:Trembler/tilt switch was Maxim truck hijacked
>
>
><Jinx is considering trembler/tilt detection for his young 
>enterprise club
>project>
>
>Back in the dark ages crystal phonograph cartridges had 
>removable needles. By replacing the needle with a mass and 
>putting it on the bed next to a sleeping person one could 
>"see" breathing motion and even the recoil from the heart 
>pumping on a 'scope or strip chart recorder.
>
>While clearly not a "tilt" detector, a mass on a piezo element 
>might give you, and those gals in your club, a cheap jiggle detector...

Some of the cheaper car alarms use exactly this scheme.  You need to
limit the maximum possible excursion of the disks as the peizo material
is very brittle, i.e. dropping it or knocking it hard could be enough to
damage the disk.

The higher cost alarms (e.g. clifford) use an inductive sensor,
essentialy a coil of wire next to a magnet which is mounted in a rubber
suspension.  More robist and the rubber suspension makes the system
naturaly damped.  It may be possible to adapt this to the tilt sensor by
using a hall effect sensor instead of the coil.

Regards

Mike

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