A dog whistle is a type of whistle that emits sound in the ultrasonic range, which people cannot hear but some other animals can, including dogs and domestic cats, and is used in their training. We, humans can hear up to 20 kHz, but dogs can hear ultrasound (sound ranging between 20 and 30 kHz) also.
Francis Galton came up with the dog whistle in 1876 while performing experiments on the range of frequencies that can be heard by animals, which he chronicled in the book, Inquiries into Human Faculty and its Development. To human ears, a dog whistle makes only a quiet hissing sound. The advantage of the dog whistle is that it doesn’t produce a loud irritating noise for humans that a normal whistle would produce, so it can be used to train or command animals without disturbing nearby people.
Dog whistle circuit
Here’s a circuit that generates 21 to 22 kHz (frequencies just above the audible range), so it can be used to call your pets by generating ultrasonic sound.
IC 555 is used as an oscillator. By adjusting the preset, ultrasonic sound of 21-22kHz frequency can be generated. Whistle effectiveness depends on the speaker used. Use of a low-wattage tweeter is recommended. (Don’t use an ultrasonic transducer, because it is designed for 40 kHz only.)
The circuit works off 9V. For portability, use a 9V PP3 battery and house the unit inside a pocket radio cabinet.
The article was first published in July 2005 and has recently been updated.