Oscillator to pulse between 16 & 18kHz

You could do it with 1/3 of a 74HC14, two resistors, two capacitors, one diode and a power MOSFET.

... and a gaggle of lobbyists and lawyers and PR staff and sales force. This thing isnt going to sell itself, and you'll need the lobbyists and lawyers to get the local town councils to approve this kind of thing.

Don't expect me coming round your place any time soon - I'm past 40, but I can still hear 16kHz just fine (not 18, though).

But anyway:

Try making two square-wave oscillators (I don't care what kind - use a dedicated oscillator chip, or a couple of CMOS inverters), one at 16kHz, one at 18kHz. Exact frequency is obviously not critical. Switch between them with a couple of NAND gates, or a 4053 or some such, using the output of a third square-wave oscillator. Take the output, feed it through an opamp-based Sallen-key lowpass filter (12dB/octave, or better yet two stages so 24dB/octave) to knock out everything over 18kHz, so you don't fry your tweeter. Make sure you use opamps that have gain well above audio range, so that the filter math works. Run the output of that into any decent-ish hifi amp, and into a compression driver.

Total parts count, excluding the hifi amp and a $5 wallwart power supply, should be about three ICs and a handful of Rs and Cs.

Two hints:

1. Dispersion patterns at those frequencies are a bit tweaky. You may have trouble covering a decent area.
2. This will work until a clever teenager figures out how to disable the system. Teenagers are, in general, both clever and motivated when it comes to disabling systems. Some are also vengeful.

Or, you could try friendlier approaches.

In a weatherproof housing, that will work at all temperatures, even though teenagers are throwing rocks at it?

Interesting how "teenagers" are considered as if they are a separate, undesirable species. I wonder how compelling it would be if the copy said "drive away future customers"?

We had a problem around here where the movie theater owners decided they didn't like teenagers "loitering" around the outside of their premises.

They had the police come and arrest a bunch for "curfew violations".

One parent arriving found his teenager not waiting at the curb as expected, but instead under arrest.

All hell broke loose. A parents group decided that their children will NOT got to AMC theaters.

Things have suddenly gone very kissy-kissy, with special pricing, no enforcement of curfew in front of the theaters, etc ;-)

It seems to me better that kids are going to movies rather than to beer parties out in the middle of the desert, as my teenagers were known to do... I don't know how I survived being a parent... now I have teenage grandchildren :-(

...Jim Thompson

Another way is to play good classical music, Mozart, Beethoven etc. The kidz cant stand the quality

martin

"George Gosbee" schreef in bericht news:zSGKf.31016$ snipped-for-privacy@fe3.news.blueyonder.co.uk...

George,

The cost is not in the electronics. There have been times you'd start with six small signal transistors and one power transistor. A smart designer could even reduce the number of transistors required. These days one tiny micro and a power amplifier will do the same trick. But... You'll need a tweeter that can handle that 85dB for quite some time. Normal audio tweeters cannot do it. A lot of them cannot even handle a normal sine wave of one frequency for more then a couple of seconds. And you need an enclosure that can withstand pretty rough treatment. Besides, do you really think you can keep away young people using such a thing? I doubt it. Maybe in your part of the world but not in Rotterdam. The best that can happen, are the local authorities summon you to remove it. Don't want to think about the worst.

petrus bitbyter

What makes you think "noise" will "repel" "teenagers?" Making noise is one of their primary functions in life.

If you just wanna make noise, get a sonalert.

Good Luck! Rich

The cleverness, if any, in the product is that it uses high frequency sound that most adults cannot hear and many youngsters can. Sonalerts are usually in around the frequency of human scream, and most everyone (the deaf aside) can hear them clearly.

Best regards, Spehro Pefhany

Oh, hell, then. Just play some Rachmaninoff or Wagner cranked up to 11. ;-)

Cheers! Rich

Are similar things not sold to keep cats and dogs out of your garden? I suppose they will cost less than 500 pounds. Maybe they need a bit of retuning.

Wim

Best idea yet. Will give it a go.

George.

See,

George.

Not Beethoven! See "A Clockwork Orange" for details why.

ing

I think one has been installed by a council in this part of the UK, I remember seeing something about it on the local TV programme. Some years ago experiments were conducted in an underground station in London, playing classical music to drive loitering teenagers away.

Leon

Ah, One film I have never seen, I wus thinking about the late piano sonatas, dunno if they where in the film

martin

martin

OT.

Have you got anywhere with the AL3101? I saw some messages, by you, a long time ago on the wavefront forum

martin

eeding

i=2Ee.

hts?

I've been concentrating on other things.

Leon

eeding

i=2Ee.

hts?

I've been concentrating on other things.

Leon