Ultrasonic dog chaser made by NE555

It is said that many animals have a particularly developed sense of hearing and can hear higher frequency sounds that humans cannot hear. Many commercial pest repellers are made based on this principle, and their frequency range is usually between 30 and 50kHz.

The principle of this design is the same, but it is different. This is a powerful audio/ultrasonic generator that can be used to drive away dogs. With it, you can make your beloved dog quiet down at midnight and stop barking or subdue other people's vicious dogs (probably thieves will like this thing very much).

As far as I know, dogs and some other similar sized mammals behave very differently with insects. Dogs respond to each other at frequencies between 15 and 25kHz, with older dogs producing sounds at higher frequencies. This means that dogs cannot hear the sound of a normal ultrasonic insect repeller.

Therefore, I decided to redesign a circuit (of course, based on the most commonly used 555), using a variable resistor to change the frequency and a piezoelectric buzzer that can make a relatively loud enough sound - 82dB.

The circuit is very small and can be assembled in less than half an hour. The values ​​of most components are not very precise, but you should be aware that these values ​​may change the frequency produced. Adjustment of the variable resistor: larger resistance makes the frequency lower. Since different dogs will respond to different frequencies, you may need to experiment and adjust the circuit.

The circuit is very simple and may be a piece of cake for you. The 10nF (0.01uF) capacitor is very critical, it determines the frequency. Most ceramic capacitors are very unstable and the error is about 20%, which is not very easy to use. Therefore, it is best to use a polypropylene capacitor with stable performance. A larger capacitance value means a lower frequency.

During the adjustment process, an oscilloscope is necessary. Since I don't have an oscilloscope, I used Winscope. Although its measurement range is limited to 22kHz, it is just enough to see how the circuit works. Test whether the circuit works at different frequencies. The 4k7 variable resistor and 10nF capacitor produce a frequency of 11K to 22kHz, which is just right.

This circuit does not require an etched circuit board, a breadboard will do. If desired, you can mount the circuit in a small plastic box, and you can add a LED as an indicator. The circuit consumes very little power, and a 9v battery will work for a long time.

Further experiments: I used an amplified version of this circuit to make a louder sound. Further attempts have not been successful, mainly because the high-frequency characteristics of the 555 have deteriorated. Perhaps I must use a frequency doubling circuit - I don't know if my idea is a little wrong. Another use of the circuit is "a simple device to prevent dogs from barking". Add a sound trigger switch to this circuit and set it to: as long as your dog barks in the dark, it will emit an ultrasonic buzzing sound. After a period of training, your dog will not bark at night.