Ok, first off, this does NOT kill or harm dogs. Just annoys them. The device was created by Steve Gibson, one of my idols, when he was 12 or 14. He is a computer security expert and programmer, host of the Security Now podcast from TWiT and developer of the hard drive repair program Spinrite as well as many other awesome stuff.
In short, the Portable Dog Killer, or PDK, was made to address a problem of a dog who would bark and scare people. His solution was to make a focused sound generator set to the tune of 16 KHz. Human hearing is 20 to 20,000 Hz, or 20 KHz. The tone is low enough he to hear it to make sure it worked, but high and loud enough that it irritates the dog. He succeeded to train the dog to stop charging the fence and scaring people. Of course, being a middle-schooler, you can bet he took it to school to show his friends.
This is where the PDK catches my attention. He and his friends at school would point the PDK at seagulls and fire! The seagulls reaction, according to Steve, “what [PDK] did was it nearly knocked the seagulls out of the sky.” Eventually the seagulls learned to stay away from the beach. He talks some about how he built the device, including the most important part, the 555 timer. Looking for the 555 timer has found me both how to wire the 555 timer in general to make a tone or flash lights, as well as full plans for the PDK. More about that plan, the PDK 1.5 in the next post.
From the guy with his eye on the sky, Travis...the camping lifeguard