Hi,

here are my thoughts:

Your original post implied that you had two sensors (mic's), to get a
pressure difference inside and outside the bag.  You will need to do
this if there is a lot of ambient noise (e.g. in a gym there will be
music playing and people shouting (probably because the music is too
loud)).  If you use a mic you will always have this problem.  If you use
a mechanical sensor you won't.  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,
and if it resets every time (which it doesn't have to do in a car
crash!).  Otherwise you need a weight on a spring with a sensor to
detect the movement, or a crushable sensor with a piezo element.

Sorry if these thoughts are a bit disjointed, but I'm not really
concentrating.

Bye

Andy (the other one)

>----------
>From:  &Ltwouter Suverkropp[SMTP:Wouter.Suverkropp@JET.UK]
>Sent:  20 August 1996 12:44
>To:    Multiple recipients of list PICLIST
>Subject:       Re: Any thoughts on this one?
>
>Hi,
>
>just some thoughts:
>
>a) Try a dynamic microphone
>b) try a small speaker as 'microphone'.
>c) try something piezo. Probably the cheapest option.
>
>All these draw zero power, and all should be well below 0.50usd in
>quantity.
>In fact, a few good punches with the microphone or speaker may just be
>able
>to power your circuit, no?
>
>Why are you measuring outside the bag as well? Does the impact inside
>the bag
>not provide you with enough information to determine wether the next
>punch is
>harder or less hard? Do you need accurate calibration? I could imagine
>a
>piezo strip, glued to a board on one end, provides you with a good
>vibration
>sensor. At the cost you mention for a pressure sensor you should be
>able to
>buy an automotive accellerometer (sp?) as used for airbag deployment.
>
>Hope this helps,
>
>Wouter.
>