It is said that many animals in the sense of hearing developed, to hear the humans can not hear high frequency sounds. Many commercial pest control is based on this principle driven manufacturing, usually in their frequency range between 30 to 50kHz.
The same is true of the design principles, but different. This is a Powerful audio / ultrasonic generator, can be used to drive away dogs. Use it, you can let your dog quiet at midnight, no vicious dog barking or the surrender of others (probably thieves would like this thing.)
As far as I know, dogs and other mammals and insects, like the size of the performance is very different. Between the dog’s voice response between 15 and 25kHz, the old dogs some of the frequency of the sound will be higher. This means that ordinary ultrasonic sounds emitted by insects, driving, dogs can not hear.
Therefore, I decided to design a circuit (of course, is based on the 555 most commonly used), use the variable resistor to change the frequency and use a relatively large enough to send the sound of – 82dB piezo buzzer.
Circuit is very small, you can assemble it in half an hour. Most of the components of the parameter values ??does not require very accurate, but you know these values may cause the frequency generated by change. The adjustment of variable resistor: the larger the frequency of resistance so low. Since different dogs will react to different frequencies, you may need to experiment on the continuous adjustment of the circuit.
Circuit is very simple to you may be trivial. 10nF (0.01uF) capacitor is critical, which determines the frequency of working up the majority of ceramic capacitors is very unstable, mostly in the 20% error, very easy to use, so the best hope with stable performance polypropylene capacitors. Large capacitance means lower frequency.
Adjustment process, an oscilloscope is necessary. Since I did not scope, so I used the Winscope. Despite its limited measurement range 22kHz, but just to see how the circuit works. Test circuit at different frequencies are able to work. 4k7 variable resistor and 10nF of capacitance of the frequency of 11K to 22kHz, this just fine.
This circuit does not require etching circuit boards, test boards on the line. If necessary, you can install the circuit into a small plastic box, you can also add a light-emitting tube made of light. Circuit power consumption is very low, a 9v battery to work for a long time.
Further experiments: I use this with a magnified version of the circuit to issue a greater voice. Further attempt has not been successful, mainly due to the high frequency characteristics of 555 variation. I must use the multiplier circuit is probably – I do not know what I think is a bit wrong. Another use of the circuit is "a simple device to prevent dogs barking," added a voice to trigger the circuit switch, set to: as long as your dog barking in the night, the hum of ultrasound on the issue. So after a period of training, your dog barking at night was not.