Positive feedback circuit ??

[robdog]

Hi everyone, I have an idea for a circuit but I don't know how it would work / if it can work...

I have a piezo-composite actuator, which is basically a paddle (a bit like a 6" ruler) which will bend if you apply a voltage across its two end terminals. As with other actuators, it can be used in reverse, i.e. you can move the paddle and get a voltage signal out. If you flick the paddle (like twanging a ruler on a desk) it will produce a sinusoidal wave.

Would it be possible, using some sort of positive-feedback mechanism, to build a circuit which, as soon as the actuator is flicked, positively re-enforces its own signal and exponentially resonates itself? In other words, is there a way to take the signal produced by the actuator, amplify it and feed it back into the same terminals so that it continues resonating forever?

I'm mainly confused by the fact there are only two terminals on the actuator, so how can you use them as an input and an output at the same time?

Hope that all makes sense. Any help appreciated!

-Rob

 

[mneary]

Yes, oscillators with piezo elements in resonance are very common. Maybe google 'ceramic resonator oscillator'.

 

[mbarazeen]

may be you can try connecting a capacitor across, a certain value may keep it oscilating until it loses its energy given manually (bending)

 

[robdog]

Yes, oscillators with piezo elements in resonance are very common. Maybe google 'ceramic resonator oscillator'.

Thanks. I tried this but it seems that ceramic oscillators are constructed differently to my piezo-based paddle, which only has two terminals rather than three (as on most ceramic resonator elements). Also the frequencies I want to work with are much lower - in the lower audio band, e.g. hundreds of Hz.

Anyone with any advice on how to do this? Or how ceramic resonator circuits might be adapted for this?

 

[robdog]

Anyone?

 

[MrAl]

Hi,

Oscillators are very common in electronics. You can build a circuit to actuate the paddle i bet with just an oscillator of some sort. Tune it to whatever frequency you like.

 

[Pommie]

You could pulse it, the same as a clock pendulum is kept swinging. You need to detect a certain point in the cycle, say as it begins it's stroke in one direction and give it a pulse to give it a little kick in the same direction. This will add sufficient energy to keep it oscillating.

Mike.

 

[robdog]

Thanks everyone but I don't want a simple oscillator..

What I want to do is specifically drive the paddle with its OWN waveform, generated by displacing it in the first place. The idea is that this will produce a wave shape that is not quite a sine wave, but a shape which is governed by the properties of the paddle... or so I think :s

The idea is to hook it up to a loudspeaker and get a sound that is not just a sine wave as would be generated by a simple oscillator.

Does that make sense?

 

[mbarazeen]

in this case you shold work in different idea, you want to paddle it using some voltage meantime you need an ouput to observe/ hear it, but you have only two terminals.
so you can use a switching device that will give a short paddling by switching a voltage, and then switch it back to an audio aplifier. when the level drops bellow a value, it will again automatically give a paddle by switching.
if the duration of paddling is very short, then you may not recognize the short break in the audio output.