I'm a bit confused with respect to selecting a piezo buzzer for this project. While the circuit seems to dictate the output frequency, in this case 10KHz - 22KHz, when looking at piezo buzzers there are varying resonant osculating freq.
to select from. How do I know what to get for this circuit?

Thanks

View attachment Dog_Whistle.PDF

 

Looks like you really need a transducer instead of a piezo. A true piezo buzzer will have a fixed frequency that you can't change more than a small fraction of a percent. The test circuit is depending on switching in a large value cap so that the output is within the hearing range of humans.

 

Looks like you really need a transducer instead of a piezo. A true piezo buzzer will have a fixed frequency that you can't change more than a small fraction of a percent. The test circuit is depending on switching in a large value cap so that the output is within the hearing range of humans.

Something like this?
Ultrasonic_Transducer

 

Sorry there were no specs on the piezo device I posted above. The article also offers the ability to use a piezo horn tweeter, but for me I think they will be too expensive and too large for the application. ....so I'm still at square one with respect to understanding piezo sound devices and the specific one needed for this design.

 

The 40kHz ultrasonic transducer won't have any output at audible frequencies.

Here is the horrible frequency response of an "ordinary" piezo transducer. It has peaks and dips all over the place. It should be driven at a frequency where it peaks.

 

The 40kHz ultrasonic transducer won't have any output at audible frequencies.

Here is the horrible frequency response of an "ordinary" piezo transducer. It has peaks and dips all over the place. It should be driven at a frequency where it peaks.

OK, for the above mentioned circuit, what do you recommend?

 

If you use an "ordinary" piezo transducer then you must adjust the frequency for a peak in its frequency response.

 

If you use an "ordinary" piezo transducer then you must adjust the frequency for a peak in its frequency response.

I have yet to find a Piezo with a freq range between 10KHz and 22KHz.

 

I have yet to find a Piezo with a freq range between 10KHz and 22KHz.

Cheap "guitar" speakers have a piezo horn tweeter that has a frequency response from 4kHz to 27kHz. But since they have so many peaks and nulls (smoothed out in the graph) then they sound like a whistle.

 

Cheap "guitar" speakers have a piezo horn tweeter that has a frequency response from 4kHz to 27kHz. But since they have so many peaks and nulls (smoothed out in the graph) then they sound like a whistle.

Not sure I want to carry a 3" square tweeter around in my pocket.

Perhaps something like this:



Planet Audio P18TW 3/4-Inch Soft Silk Dome Tweeter

 

Amazon and Planet Audio do not have detailed spec's for the expensive silk dome tweeter. Speaker spec's are supposed to show their frequency response.
It is a coil and magnet speaker that is only 4 ohms so a 555 cannot drive it. It is made for intermittent audio, not for playing continuous sound. Its max frequency is 20kHz, not 27kHz but no spec shows how far down is its output at 20kHz.

 

Specs:
3/4-Inch Soft Silk Dome Tweeter Neodymium Magnets Surface, Flush And Angle Mounting Kits
Power Handling (Peak) 50W
Power Handling (Contin.) 25W
Frequency Response 4Khz-20Khz
Efficiency (1 Watt/1Meter) 91 Db Impedance 4 Ohm

Another Tweeter from Pyle has different specs:
Technical Details
1" Mylar Dome - Frequency Response: 2khz-24khz
High Density Neodymium Magnet - Spl: 100db @ 1w/1m
Tri-Mounting System: Pivot/Angle/Surface - Power Handling: 60 Watts RMS/120 Watts Max
Ferro Fluid Cooling - Includes Custom Mounts, Wires and Installation Hardware
Integrated Crossover System

I don't doubt that the 555 alone will not power the tweeter, but adding an amplifier section as in the design writeup ought to be able to handle that I assume...

Brand Name: Pyle
Model: PLWT3


http://www.amazon.com/PLWT3-1-Inch-...s=electronics&ie=UTF8&qid=1315711696&sr=1-125

 

A hi-fi tweeter is very fragile and is made to produce the intermittent low average power of high frequencies such as t, s or ch sounds in speech or in music from cymbals.
The "continuous" power rating is when music or pink noise with an average power is playing, not continuous tones.

A piezo transducer can be used for continuous tones.