accerelometers

An accelerometer might work, but Knowles has a microphone that uses similar technology:

I've just bought a couple to play with.

Leon

The most similar application that I know are the so called knock sensors. They are piezoelectric accelerometers (actually they are microphones with a mass applied to the moving part) and they are used to detect "knocks" (detonation waves that follow the spark ignition) in gasoline/diesel engines. Maybe if you use this as search string, you may find something useful...

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- asd -

Another product to search for is alarm system window break detectors.

How well does it work?

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Best Regards,
Mike

I made myself a nice little accelerometer using three 10p piezo microphone/ sounders (the birthday card sort) soldered together in the form of a tetrahedron, with a ball of blu-tack in the middle. A little maths to resolve the direction, and off you go.

Paul Burke

Pretty abysmally I suppose, but good enough for the cheap demo of vibration detector alarm that I was doing for a prospective customer, i.e. I could show him that I could detect the unit moving, tell if the move was vibration or the thing was being picked up or rotated, tell him that the (simulated) Diesel had stopped. The project went no further, but that's another story.

I'm sure that with a bit of development it could be quite OK for many similar applications.

Paul Burke

sounders (the birthday card sort) soldered together

He omitted all the corners, in his post. They likely auto-created themselves. He did mention what you, (being geometrically minded), might think of as the faces. I expect 3 physical faces would suffice to build something with the form of a tetrahedron. The 4th face would have to be virtual. Maybe that is why it has only the form, rather than actually being, a tetrahedron.

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You can also use Piezo

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs

Who be OP?

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    Boris Mohar

"Michael Peters" wrote in news:cp46vl$vh0$03$ snipped-for-privacy@news.t-online.com:

Check out Bruel & Kjaer. See

. They have an article about how they used an accellerometer to measure a cat's purr.

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Sooner dot boomer at gbronline dot com

'hedron' means 'face', not 'corner'. A tetrahedron has four triangular faces. If you fix three discs together in 3 dimensions, the fourth face is void.

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Three sides, the fourth being open. I couldn't see what a fourth sensor would contribute.

Paul Burke

I can't see why a tetrahedral shape would be a good idea. I would put the three at right angles, and extract the information for each axis without recourse to trig.

d

Pearce Consulting

I'd like to see a gemetrical diagram of a tetrahedron with only three corners. Sounds kinda self-contradictory. Did you omit the

4th corner?

Yes, but (a) it looked nice and (b) it held the ball in place.

Paul Burke

How come it didn't fall out the open side?

d Pearce Consulting

because contact microphones are quite different from accelerators, and give different results. Now I don't really know much but it seems to me that accelerometers are much more sensitive than contact microphones.

I became interested in accelerators after reading an online article (sadly, without sound examples) of scientists who used them to record the sounds of insects in very high quality by fastening accelerometers to the twigs that the insects were sitting on. I don't think contact microphones.could do that very well. Of course I haven't tried yet.

Anyway, this seems to be a pretty exotic subject and nobody could answer my original question so far (except for one who pointed me to

-Michael