Dana
>
> >In any case you need to know the rate of
> >change of the signal (= acceleration) so you can get the force that has
> >been applied to the bag (F=ma) where m is the mass of the bag.  An
> >airbag sensor is probably best but only if it has an analogue output,
>
> This is a very interesting idea. Mounting an accelerometer within the
> product case (on the surface of the punching bag) would provide much better
> information on the forces and energy expended by the boxer. The bag pressure
> method used has many sources of error. Only two problems though (sigh)...


You might want to look into carbon mic's. The carbon mic's work by changing
resistantance due to compression of internal carbon particles. The same
particles will compress with acceleration. They don't cost much.

Walter Banks
http://www.bytecraft.com