At 08:20 24/09/97 +0100, you wrote:
>Firstly "Thanks to all who responded to this thread so far" Your Ideas have
>been an insperation. In fact I have now concluded that I probab;y don't
>actualy require an Accelerometer but a 3 DOF movment detector, I am trying
>to build a small device that I can attach to my snowboard that will sound a
>LOUD alarm if anybody tries to "Borrow" it without my permission.

I have several suggestions.

The traditional tilt switch is a mercury switch. It comprises a ball of
mercury and some contacts. If it's tilted the mercury moves breaking the
contact. The main disadvantage is that it only covers a small range of
angles so you would need to stow your board the same way each time.

Another neat trick is to use a spring and weight system, similar to those
used in pinball machines to detect tilting. These are particularly sensitive
to sudden movements. You need a piece of piano wire which is fixed at one
end, and passing through a ring at the other. In the middle you attatch a
sliding weight, and adjust it so the wire doesn't quite touch the ring. Any
sudden movement and the piano wire touches the ring.

I'll try and sketch it here...

      ____                   .
      |  |---------WWWW-----(-)-
      |  |                   |
------+--+-------------------+-----

This will detect motion along two axis, and two of them, along each side of
a box for example, should detect acceleration along any axis. Main weakness
is that they don't detect very small forces.

Hope this helps,

Keith.



------------------------------------------------------------
Keith Dowsett         "Variables won't; constants aren't."

E-mail: kdowsett@rpms.ac.uk  or kdowsett@geocities.com

WWW: http://kd.rpms.ac.uk/index.htm
     http://www.geocities.com/CapeCanaveral/Lab/8979