>a) Try a dynamic microphone

Good idea, but far too expensive.

>b) try a small speaker as 'microphone'.

Even better idea, but I hav'nt been able to find one small enough (1/4"
6.35mm). Small earphone speakers don't have permanent magnets and are
mounted in such a way that they won't produce any output at all for pressure
pulses.

>c) try something piezo. Probably the cheapest option.

Yes, this is where I have been concentrating. The main problem is their
extreme sensitivity to vibration. Just slapping the bag lightly produces
significant output energy. Tapping the product case (mounted on the surface
of the punching bag) is interpreted as a massive punch.

>In fact, a few good punches with the microphone or speaker may just be able
to power your circuit, no?

Would'nt that be great! Unfortunately, No. There is an end-of-round buzzer
that is power hungry.

>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?

Thats an interesting question. Inside the bag the pressure wave would be on
all sides of the sensor and little output would be produced. UNLESS, the
sensor had its own little pocket of air with a restricted airflow port. The
sensor would have to be airtight except for this port, otherwise variation
from one sensor to the next would be too great.

The other answer is that the computer case is strapped to the surface of the
punching bag. It needs to be removed to change batteries, etc. The sensor
sits on the end of a small tube which fits into a hold in the surface of the
bag when installed.

>Do you need accurate calibration?

The customer expects accuracy, but my feeling is that there are far too many
errors in the setup. The force of the punch is affected by the size of the
glove, where the bag is hit, what the temperature is, the continion of the
bag over time, etc.

Right now I'm aiming for sensor consistancy.

>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.

I'll look into that idea. I hope the price (in quantity) would be closer to
the target though.

>Hope this helps,

Yes, it certanly does (Leutenant?) Wouter. Thanks.

If anyone knows where to start in sourcing airbag accellerometers, please
speak up!  :-)

Regards, Dana Frank Raymond
dfr@icom.ca