On 01/30/2011 10:26 AM, Don Foreman wrote:
On Sat, 29 Jan 2011 23:32:21 -0800, "Steve B"
wrote:

I subscribed to some electronics newsgroups, but as of yet haven't passed
through their process to get messages.

I want to build an ultrasonic dog repeller. I do real estate inspection,
and there are times that I encounter either obnoxious dogs or aggressive
dogs. I carry pepper spray, and have almost had to use it, pitbulls both
times.

I have this little blue box that works pretty good on my two dogs when they
raise Cain from a visitor or a knock on the door. But its range is not that
good. It runs on a 9v. battery, and is a Big Lots item.

I would like to build one that is very strong, both for gaining some range,
and gaining the dog's attention.

Researching this, I find the 20,000 - 60,000 hz. range to be within their
hearing. Is there anywhere I can buy a simple tone generator, or kit that
will let me build one of these. Is tone generator what I need to be
searching for, or is there another term?

I see several on the market, but they are lax to state just how strong they
are, or their range, mostly seeming to be aimed at home training at short
distances.

TIA

Steve

It's best to keep the freq just above human audibiilty, so somewhere
between 22 KHz and 30 KHz.

The self-resonant piezo transducers generally cannot deliver much
power, except for those used in humidifiers and cleaners, but they
couple to water rather than air.

The good old 555 timer makes a fine tone generator for considerably
less than a buck.
http://www.national.com/ds/LM/LMC555.pdf

You would then need an amplifier to get this up to about 24 volts
peak to zero. A couple of transistors can do this. You'll also need
two 9-volt or 12-volt batteries.

This tweeter can deliver a sound pressure level of 94 dB at 25 KHz for
$1.80:
http://www.parts-express.com/pe/show...number=270-011


An alternative: make a Hartmann whistle that runs off a can of freon.
That might take some experimenting, and the sound pressure levels they
can generate could be dangerous.

Most of us on the group can't hear 25kHz any more, but when my sisters
and I were kids (my sisters up to their late 20s) you'd have us
experiencing pain with a loud noise at that frequency.

If you want to get it above the range of the hearing of all humans, not
just geezers, make it 30kHz.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html