power a led with piezoelectricty

ninja.lion

I hae aqiured a piezo disk and LEDS but it will not power them. i do not know if it is the disk or an led. I tried the LED with AA AAA and D batteries but only turned on with 9V they are sea green

mfb

Without that description, it is hard to find out, but I would expect one of those reasons:
- voltage too low
- current too low
- time the piezo disks supply that voltage and current too short

The LED should need something like ~2-3V.

ninja.lion

so how do all the videos on youtube of someone poking a disk and the led soldered to it lighting up work?

Nugatory

They've chosen a combination of disk and LED that will work - the disk produces enough voltage and current to activate that LED.

ninja.lion

how would you find a combo like that

NascentOxygen

Can you provide a link to a good one?

ninja.lion

http://www.youtube.com/watch?v=Xuw9frP1GNo

NascentOxygen

I'm surprised to see that small piezo produce sufficient current to flash a LED. He doesn't seem to be tapping it with much force, either.

ninja.lion

My disks are 3.7 cm in diameter what type of led should i use.

by the way thanks for the help

NascentOxygen

Try it at night in the dark, to see whether you can discern any flash.

I'm not sure whether polarity must be observed, but try reversing the leads.

This somewhat dated reference says that Green LEDS based on InGaN technology work the best for low currents. http://donklipstein.com/ledlocu.html

The LED in that youtube video was green. Does the author there indicate what he used?

ninja.lion

thank you very much I will try with green LED I will also try using more than one disk at a time. just wondering i sodor the WIRES to to metal disk and the smaller part of the crystal disk that is seprsted from the rest

NascentOxygen

If you are unsure which are the terminals, try connecting a multimeter (voltmeter) between the likely places, and tap the piezo. I expect you'll see a voltage jump when you have the right spots.

ninja.lion

i tried that no voltage

NascentOxygen

You tapped it while you had the voltmeter connected? Maybe that piezo is dead, do you have another one to try?

Do you have an unwanted radio earpiece (or phone earpiece)? Try connecting two wires from the piezo to two of the earpiece plug connections. Hold the earpiece near your ear, not in it, then tap the piezo. I don't know whether this will work, but with luck you'll hear a click. You'll have to experiment to find the right connector pair on the plug. As you'll see, you need 4 or 5 hands to perform this.

If this doesn't work, then I think I'm out of ideas. You don't have access to an oscilloscope, do you? If the piezo is working, the voltage would show up well on it.