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Name: Steve
Status: educator
Grade: 9-12
Location: CA 
Country: N/A
Date: 1/25/2006


Question:
Is it possible to create a Piezo crystal / led substance that lights upon applied pressure? Could the Piezo crystals and leds be formed together in a very small fashion so as to be incorporated into plastics or paint for example?>


Replies:
Piezoelectric crystals produce a change in voltage in response to a change in strain (usually produced by putting some load on them). However, the crystals produce an electrical output only when they experience a *change* in load. So as soon as you stop changing the load (by pressing harder or more lightly), the electrical output would stop. So some other electronics would be required to collect the charge and sustain it for a useful amount of time (like a capacitor, for instance). The voltage produced by the piezo crystal also varies depending on how hard it is pressed, so something is necessary to regulate the power produced.

In addition, the current through an LED needs to be controlled to avoid damage and to control the brightness. Most LED's achieve their rated cycle lives with about 20 mA of current. More current reduces their lives (but increases brightness). So again, some additional circuitry would probably be required to control the current so the LED would act the way you want and last as long as you want.

So producing a single substance that would do what you describe in a consistent manner is unlikely. However, with the current state of miniaturization that is available, it is most likely possible to produce an electronic module with integrated piezo transducer, LED and current-conditioning circuitry all contained in one unit.

Hope this helps!

David Brandt, P.E.



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