Feb282011 Submission - Megaphone "Portable Dog Killer"

Disclaimer:  First, before everyone goes writing me about how vile of a person I am because I made a device that kills helpless animals, please read the entire post.  This device does not actually kill or harm dogs or any other living creature in any way shape or form.


Recently I had a problem in the neighborhood whereby a couple of "aberrant K9's" were getting lose because the irresponsible owner would not repair the hole in his fence that was allowing them to escape.  The problem got so bad one day when returning from the grocery store, I found myself trapped in my car under seige by these animals.  Every time I tried to exit my car they would approach me aggressively. Not one to test fate the police were called, but by the time they responded, the animals were no where to be found.  It was not uncommon for these animals to get loose several times a week.

One day I was listing to the Security Now! podcast and Steve Gibson was describing a story from when he was a kid when he constructed what he called a "Portable Dog Killer" (here is a link to the mp3 of that podcast). While he didn't give specifics of the circuit, he did mention that it contained a 555 timer and a piezoelectric speaker.  Using my imagination I could piece together what he did.  His results with his homemade gadget were spectacular.  I began to think...   What if I took that concept and fed it in to a megaphone.  Megaphones are perfect... They are designed acoustically to be loud.  I quickly ordered up the biggest, loudest megaphone I could find (without breaking the bank).

Now I should say I am an amateur with electronics.  I am not an engineer or an expert by any means.  I can copy a formula for frequency and plug in my own values (such as the formula for freq), but beyond that I am lost.  So my first pass at bread-boarding failed because the output of the 555 could not drive the cone directly.  I had read that mosfets can be useful for driving high current devices so I wired one in... Success.  This is still a work in progress.  The name "Portable Dog Killer" is a a tribute to Steve Gibson.  On a quick side note, please check out his site at I highly recommend listening to the podcast linked above,  it is supremely entertaining and inspiring for any aspiring maker.



Video of me testing out the breadboarded  circuit

(ATTENTION JUDGES This video is of an early prototype version posted here to show my progress with this.  Please see the 2nd video below for the final version of the contest submission)


Circuit Boards arrived from BatchPCB, They are great... I order 2 they send me 3!!  They do this all the time, they sometimes need to fill up a panel, so they send you the extras free of charge.

What a value!


Here I am exploring the limits of warranties hours after ownership on this new Megaphone....

Assembled board in the Megaphone.

Close up of a knob I installed to vary the output frequency (from 8HZ to 22KHZ)

Here is a picture of the finished unit (looks basically like a generic megaphone)

Here is a video of me bench demoing the unit (sorry, no video of me testing this on actual animals)

***ATTENTION JUDGES*** The video below is the current version and represents the contest entry.

Screen-shots of The Spectrum Analyzer.  The First is Frequency turned down to about 8k, the 2nd, turned up to 19k.


Fortunately Animal Control dealt with the Dogs problem before I had to use this, so my development on this has been put on hold for now.  But should the hounds of hell come knocking on my door, Ill be ready.

What does the future hold?

Well for one I would like to make it louder.  I will probably reinstall the original megaphones circuit via a switch. In addition to that, I had worked out an arduino based frequency counter (picture below).  I had thought of doing a digital read out of the frequency.  I suppose if I do, I could have the arduino generate the tone as well,  but what is the fun in that?  The 555 is so perfect at what it does, it has an infinite number of uses and I am glad I had the opportunity to share this one.  I look forward to learning a lot more of what it can do via the submissions to this contest.  Thank you for your time.

Picture of Arduino based Freq counter test using an earlier version of the board (pre-mosfet)

If you want to reach me you can feel free to email me at tminnick at gmail or you can find me on twitter here @TomMinnick


Damage Designs is born & a little about me.

Hello interwebs, my name is Damage aka Tom and I originally started up this site to enter my “Megaphone” portable dog killer in to the contest.  However I have done other “hacks” which I might document here at a later point.

A little about me:  I am an amateur electronics/computer hobbyist and unapologetic geek.  I currently work full time and at nights I am going to school to get a degree in computer science.  In my spare time I like to tinker with electronics.  I like most people, am a consumer of electronics and technology products, however I have gained a strong interest in giving back.  I eventually would like to create devices that others can use bringing the process full circle.  This blog site will serve as a place for me to document my journey from beginner to intermediate and beyond.  Over the years I have made (or modded)  everything from my own Guitar Amp Switchboards to modding a 3.5″ all-in-1 card reader to include an integrated Xbox 360 wireless controller radio.  My interests jump around a lot so you may find that I go cold on a particular project for a while.  I almost always come back to them, sometimes the time away from a particular project I may be stuck on helps rejuvinate my creativity and I am often able to approach it with new ideas.  Here are just a few projects that I am currently in various phases of development.

Arduino Powered Midi Foot Controller: My goal here to to emulate the complete functionality of the Rock-tron All Access at a fraction of the cost my own way.  Using an arduino and the midi library this project should not be too hard.  I have ideas to expand upon what they have done by adding more features, (LCD display panel, Encoder based programming option, as well as customized to work with my equipment set).  I hope to not just make a clone of what they already have, but do design something new and better from the ground up.

Arduino Danger Board: I was fascinated with the Sparkfun Dangershield as a tool for learning Arduino.  I wanted to expand this concept to an entire panel.  Complete with a keypad, LCD Display, more buttons, more pots, encoders (rotary and positional) and anything else I could cram in to the 18×12 inch enclosure I had planned for this.  My vision of it was to recreate an arduino version of those RadioShack 200-in-1 electronics kits I had as a kid.


Custom Xkeys Keyboard: Being a high fan of computer games and MMO (Specifically World of Warcraft)  I want to create a custom gaming keyboard.  The Xkeys Matrix Board seems perfect for this, it can support up to 128 keys and is ready to go out of the box.  All I need to do is layout all the buttons I want to use and wire them up.

My biggest setbacks currently are on the mechanical fabrication side of things.  I can imagine a lot of ideas, but I currently lack the skill-set & tools to realize them to completion.  With 3D printing becoming more available and cheaper as well as laser cutting, this problem will hopefully go away with further advances in technology.  Hopefully it will get to a point where I won’t need to know how to operate a mill, but rather I can draw it on CAD, point/click/upload my drawings to a machine house and for a modest price, the finished part shows up at my door.

Thank you for taking the time to visit my page.

If you want to reach me please use the contact page.  Please follow me on twitter here @TomMinnick

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