Monday
Feb282011

555contest.com 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.

Background

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 www.grc.com I highly recommend listening to the podcast linked above,  it is supremely entertaining and inspiring for any aspiring maker.

Planning

Schematic...

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!

Construction

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.

Conclusion

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

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