piezo

[Electronman]

Hi guys,

I have a question,
I used a piezo transducer (the ones which are used in clocks and cheap stuffs as speaker) to lighten a small 2mm LED, so the piezo is used as a power supply connected directly to the LED.
Now the LED lights up when the piezo receives the stresses which are generated by my finger.
Unfortunately I can not light up the LED when I put the piezo just in front of my stereo speaker (the piezo is connected to the surface of the speaker cavity and the Speaker's volume is as high as possible).
Can somebody tell me what the reason is?

Thanks a bunch

P.s Can somebody direct me if there is any rule of thumb into piezo transducers used as batteries?

 

[Hero999]

The coupling of the speaker to piezo disc isn't as good as the coupling from your finger to the pizeo disc. The disc bends a heck of a lot more when you flick it with your finger than it does when placed near the speaker when it's set at full volume.

If you placed the transducer directly on the speaker cone then you'd probably get a high enough voltage to light the LED.

Piezo transducers don't give enough power to be used as batteries. The only way I know of using a piezo to generate electricity (other than as a sensor) is in ignitions for small lighters and cookers. When the button is pressed, a thick piece of piezo crystal is struck with a pin causing it to generate a low current 25kV pulse. This is enough to light gas and zap some insects but too low energy to zap you.

 

[HarveyH42]

Piezo transducers don't give enough power to be used as batteries. The only way I know of using a piezo to generate electricity (other than as a sensor) is in ignitions for small lighters and cookers. When the button is pressed, a thick piece of piezo crystal is struck with a pin causing it to generate a low current 25kV pulse. This is enough to light gas and zap some insects but too low energy to zap you.

You obviously have never take a part one of those lighters, and played with it. Can tell you from personal experience, they deliver a very unpleasant jolt. You should try it sometime, if you don't believe it.

Part of the problem might be that the entire disc is being moved equally by the speaker, the crystal doesn't get stressed, and produces nothing or very little. Have you hooked it up to a meter? Search the web, remember somebody using them to harvest energy in a sidewalk or something not long ago.

 

[Ghosty_Ghoul]

I agree piezo ignitions will shock you but it's not much more than a static shock.