How to build a speaker using an SMD audio (ring) oscillator?

[Rhydo]

Hi!

I aim to use a piezoelectric wafer and get it to work as a loudspeaker by supplying it with a fluctuating voltage withing the audible region. I know this can be done using a simple DC to AC invertor/oscillator circuit, but the challenge is to build it as small as possible.

I looked up the working of SMD Ring-oscillators but their operating frequencies are way above the Megahertz range, so from what electronics I' am learning I don't think I can couple one of those with a piezo-wafer since the audible range of hearing for humans is 2 hertz-20 kilohertz.

Can anybody help me with this problem? Where am I going wrong? Can I actually use a megahertz range ring-oscillator running off 3.3Volts to get a piezoelectric buzzer to produce sound?

Are there SMD audio-oscillator chips available that can be directly coupled to a voltage source and be used to get a piezoelectric wafer to generate audible sound?

I have tried my best to find a solution, but I cannot see where I' am goin wrong since I cannot find any proper "SMD audio-oscillator chips" that give an output within 20kilohertz range!

ANY suggestions will be appreciated! I really need help!
Thanks in advance!

 

[Enthalpy]

First, is your piezoelectric wafer broadband? Because piezo materials give force but little displacement, matching them with air is difficult, but this eases a lot if they can be resonated and the matching acoustic components as well, so this is done in buzzers, which are narrow-band.

A ring oscillator won't go down to the audible range, but other oscillators can be very small and works directly at the proper frequency. You don't even need a divider.

Some buzzers include an oscillator, already tuned to the proper frequency.

 

[vk6kro]

You could try a circuit i have used a lot.

It is like this:
http://dl.dropbox.com/u/4222062/NPN%20PNP%20OSC.PNG

As you can see, it uses a PNP and a NPN transistor and produces narrow pulses into a speaker or an 8 ohm load.
The sound isn't very musical, but it can be very loud.

To drive a piezo transducer, which I assume is open circuit to DC, you would use an 8 ohm resistor as shown and connect the piezo device across it.

The above simulation gives an output period of about 7 mS, so the frequency is about 140 Hz. If it works as shown, the 100K resistor should be left alone and the capacitor changed to adjust the frequency.
Changing the resistor too much may cause the oscillation to stop.
You could make the resistor partly variable (by putting a pot and a resistor in series) and adjust the pot slightly to get suitable output. Be careful, though, because you can blow up transistors by reducing the base resistor too much.