Electronic question

"Steve B" fired this volley in news:togf18- snipped-for-privacy@news.infowest.com:

Steve, usually one doesn't use a separate tone generator, amplifier, and speaker for such purposes -- one uses a self-resonant ultrasonic transducer for the purpose.

It has the benefit of simplicity -- just feed power and it sings. It has the deficit of not being able to be tuned to other frequencies -- it's locked to the one resonant frequency the manufacturer assigned. (that's usually in the 40KHz range). You can also buy "bare" transducer elements, but you'll have to build up a power oscillator around them, which is more work than it's worth, considering the cost of the self- resonant varieties.

Such transducers may be had on the surplus market with outputs so small they'll barely be heard by a dog at arm's range, and powers so large they'll burn up unless mounted in a massive heat sink (or under water).

The bigger ones are used for ultrasonic cleaners and sonar applications.

LLoyd

Thank you for the simple explanation. I have seen many hand held devices, and they range from $10 to $40. They all seem to be rather wimpy in their performance. The one I have stops some dogs, yet does not faze others. I wanted to build a strong one, but don't want to have to carry it around on a two wheel moving dolly. Will investigate the transducer, and if I can find one cheap, may do an Iggy experiment on it. I have a 9.6 Makita battery that should do the power.

Steve

Steve B wrote in rec.crafts.metalworking on Sat, 29 Jan 2011 23:32:21 -0800:

In that case it's not a newsgroup. Perhaps you mean an online forum.

Why not just use the pepper spray? Bad dog owners/customers get pissed off?

The only reason they use ultrasonic sound is that people can't hear it. It doesn't affect the dog any different than any other noise. Could you use one of those canned air, air-horns?

Long ago, I saw plans for something like that in 'Popular Electronics' magazine.

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.

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:

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.

without the original context, this answer may not make sense, but for a "simple tone generator", nothing is simpler than a 555 chip. look it up on the web, see the national semi application handbook - it is one of the easiest to use chips I've come across and it is really really useful.

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.

Agree. When I was in my 20s, I could sense 26 KHz, as in ultrasonic burglar alarms used in stores. So could my then ~GF.

Joe Gwinn

Steve, an easy route to take would be to make an ultrasound whistle that is compressed air powered or even the kind that you blow air into. Most whistles are, of course, made to be heard by regular people, and those can be VERY loud and unpleasant to hear. All you need to do it build/make one that makes ultrasound. That is determined by certain chamber dimensions. Based on nothing but gut feel, I would expect that a whistle with two times smaller chamber should make two times higher sound frequency.

i

Don, I recall reading somewhere that high levels of ultrasound may not be heard, but they can still damage hearing further.

i

"dan" wrote

At times, the dogs are tied out front, or are in the back yard, and just bark, bark, bark, bark, bark ................. I cannot pepper spray them unless they are very close to biting me, or then I have a pissed off owner on my hands. I just want something to make them STFU for five minutes until I'm gone.

Again, that might scare the heartbeat out of some old fart in the area. And draw immediate attention to me.

Steve

I've had to scrap two working SVGA monitors because their H sweep was giving me headaces.

I researched this some years ago. What you say is true if the ultrasound levels are well over 130 dB, intense enough to kill mice in a bell jar. No risk with a piezo tweeter, might want to be a bit careful with a Hartmann whistle.

Earplugs.

Newb

Look up Sylvania 555.

Its an oscilating IC. You can do all kinds of things with a couple of them. Add a small amplifier and a speaker that can reproduce the sound you are looking for. You used to be able to buy a cheap amplifier kit at Radio Shack, but they may no longer be available.

Sylvania? National Semiconductor and Signetiics were the two big manufacturers. Sylvania had the ECG line, but sold it to Philips long before Philips sold it to NTE.

It's a timer than can be used in a monostable mode or an astable free running mode.

One thing that people forget is Foret an his equations...

Harmonics and sums and subtractions...

A super sonic can be heard if it 'beats' with another supersonic frequency. The difference frequency might be heard and hammers you.

I don't care for the old concept cell / telephone system we have - chops the low and high - sends middle frequency - So some of us that have loss in some frequencies have no access to the harmonics.

Mart> >

I'll bet you mean Fourier.

(...)

What about this, Steve?

--Winston