Barking Dog Repellent

[LarryH]

Hi,
Have been working on a barking dog repellent using a common "dog whistle" circuit with a 555 and boosting the output with a transistor and inductor. However, it does not appear to have enough ooomph to get a 90+ db output at 25-30 KHz. It appears a normal 4 or 8 ohm piezoelectric speaker, drags the output down to an ineffective level.

Thought maybe a high impedance tweeter might do the job but cannot find anything around 200 ohms impedance. Best I could find was "equivalent to 0.3uF" which calculated to only about 21 ohms.

So, does anyone have a circuit that would drive a "regular" 8 ohm tweeter at an adequate output or does anyone know where to obtain a high - maybe 200 ohm, tweeter?

TIA

 

[WTP Pepper]

It's down to the power you can put into the tweeter. High impedance will require a high voltage. Likewise a low impedance speaker will require high current drive.
How are you measuring the output power in the 25-30KHz range?

Most simple amplifier circuits will run at 30KHz. Google power amp chips.

 

[audioguru]

A piezo tweeter is high impedance. It is like a capacitor. It is rated for the voltage that drives an 8 ohm tweeter.
A piezo tweeter rated at 0.3uF is 17.8 ohms at 30kHz but it might not have any output at such a high frequency. If a series inductor tunes it to your frequency then its impedance is too low for a transistor to drive it. Maybe a push-pull audio amplifier can drive the series piezo-inductor.
Many piezo tweeters do not produce frequencies above 20kHz.

When you play an ultrasonic sound to a dog then the dog will probably bark at it.

Please post your schematic so we can see how your transistor can drive the series LC.

 

[WTP Pepper]

Dunno why I bother when you get no feedback one way or another.