measurement with infrared diodes

[raulrusso]

I would like to built a device to measure the displacement of a probe glued to the cone of a loudspeaker. The displacements to measure range from 30 to 1000 micrometers and resolution should be 5 micrometers or so. I think infrared diodes can be used for this application (one IR emmiter and a receiver). Can anyone tell me what are the circuits for the transmitter and the receptor? Thanks a lot.
RR

 

[IRstuff]

I don't think it's quite that straightforward. The extra weight and drag of the wires are liable to distort the behavior of the speaker, particularly if we're talking about the tweeter and midrange.

One option is to glue a small front surface mirror to the cone and bounce the emitter light off of the mirror onto a position sensitive detector (PSD). This would allow you to minimize the weight on the cone. Some tweeter cones are already metallic or metallized, so you could probably bounce the beam directly on the cone. There's a bit of calibration involved to determine the correspondence of the PSD output to cone displacement, but that can be done statically. TTFN

 

[IRstuff]

ANother option is to illuminate the probe and use a camera/macro lens to image the probe motion. You'd need to run only single frequencies, but the image smear will be essentially equal to the displacement of the probe. TTFN

 

[richs]

You might want to think about building a
Michelson Morley interferometer. You could find all the parts in one or two defunct cd rom drives/cd players, etc. Alternate sources of parts can be had from Edmund scientific. Cheap laser pointers can be used. In fact, if you are very careful, you can find a galvenometer in the cd rom drive, along with a laser, beam splitter and a mirror or two. Drive the galvenometer with the signal and a fairly high speed phototransistor to count the interference bands as they sweep through the detector. Something akin to a counter to keep track of how many bands which equate to the distance one of the mirrored surfaces are displaced. Please note that this can be dangerous as the laser has the appropriate warning on it. Further information can be had from this cal-tech document for a fun and informative construction project.

[URL unfurl="true"]http://www.ligo-wa.caltech.edu/teachers_corner/documents/interferometer_9t12.doc[/URL]

Note that you might have to cut and paste the url into
the browser in a couple of lines to get it all.

Hope this helps and let us know how it turns out!

Best wishes,

Rich S.

 

[canyoncruz]

Try Contacting Optiphase inc in Van Nuys, CA...we ran that experiment when we developed a non contact interferometric based vibrometer for measuring the flatness of hard drive discs