wrote:

Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. I`d
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

To get the air to be non-linear enough to mix the two frequencies, you would
need very high sound pressure levels that could potentially be hazardous
(or at least much more of a nuisance that whatever your neighbour is
doing). I would suggest getting a wideband microphone (a very small
electret might do, and would be less high-Q than a typical ultrasonic
transducer), and then attach a preamplifier and an electronic mixer with an
adjustable local oscillator (e.g. make a bridge from switches using a 4066
or FST3125 that alternately inverts or doesn't invert the signal). The
output of the mixer can be fed to an audio amplifier and headphones. You
can then test this receiver if you buy or borrow one of those cheap "pest
annoyer" things. Once you know that your receiver works, you could make a
parabolic reflector (e.g. spin cast a dish on an old record player from
plaster of paris in a bin lid), so that you can search for sources of
ultrasound.

Chris

John Smith I wrote:
Scott wrote:
clifto wrote:
Stace MacGuyver wrote:
Suspend a thin shaving razor blade between two pieces of dental floss
and put
your ear close to the blade. Watch the razor vibrate.

That's pretty cool, MacGuyver. Does the razor blade do anything?

It cuts off your ear if you get too close

Be better if you could use it as an electric razor ...

Replace the dental floss with Litz wire and attach ends to 110 VAC.

Wait. Maybe not. Considering how many stations you can pick up with a
razor-blade radio, that would probably interfere with vital communications
all throughout the spectrum. What's the resonant frequency of a whisker?

--
Martians drive SUVs! http://oregonmag.com/MarsWarm307.html

On Mar 10, 5:18 am, wrote:
Hi chaps,

I suspect a neighbour of a friend of mine is using an ultrasonic bird-
scarer to frighten off his pets. The man concerned won´t admit to it,
but there are times when his dog and two cats just seem to get
suddenly very distressed and hypermanic for no apparent reason. I`d
like to at least eliminate this possibility before considering any
others. So the question is, what´s the simplest way to detect
ultrasound? My web research leads me to believe the area of interest
is between 20 and 30khz. Most common bird scarers warble between these
two limits which are of course above the range of human hearing. I´ve
acquired an ultrasonic transducer that transmits on 41khz. If I couple
this up to a wien-bridge oscillator trimmed to the same frequency, I
figure I ought to be able to hear a warble if indeed this guy is using
a birdscarer, because the difference between 41khz and 20khz-30khz
will be audible to me. Is this feasible to "air mix" the two
frequencies in this simple way and hear a result, or is something more
complicated required?
Thanks!

You need your detector to be low Q since you don't know the offending
frequency. Some of these fancy sound cards do 196kHz sampling. A
piezo microphone with amp into the sound card might do the trick.

Also, as other have suggest, the bat detector.

wrote:

...

Do you really want to hear it, or have a "field strength indicator"/locater?

Why not just a mike capable of "hearing" the ultrasonic freqs in
question--feeding an opamp and meter?

Pointing the mike around should lead you into the correct direction and
following the meter reading should lead you to the source(s).

Possibly can substitute a light or even a led in series with a pot and
use a visual indication of strength ...

JS

John Smith I wrote:
wrote:

...

Do you really want to hear it, or have a "field strength
indicator"/locater?

Why not just a mike capable of "hearing" the ultrasonic freqs in
question--feeding an opamp and meter?

Pointing the mike around should lead you into the correct direction and
following the meter reading should lead you to the source(s).

Possibly can substitute a light or even a led in series with a pot and
use a visual indication of strength ...

JS



Come to think of it, wouldn't take much more to square up the sine wave
out of the opam and drop a cmos decade-divider onto that output of the
opamp and feed an ear phone with the dividers output--30,000 becomes
3,000 hz--easily "hear-able!"

JS

On 2007-03-10, John Smith I wrote:
John Smith I wrote:
wrote:

...

Do you really want to hear it, or have a "field strength
indicator"/locater?

Why not just a mike capable of "hearing" the ultrasonic freqs in
question--feeding an opamp and meter?

Pointing the mike around should lead you into the correct direction and
following the meter reading should lead you to the source(s).

Possibly can substitute a light or even a led in series with a pot and
use a visual indication of strength ...

JS



Come to think of it, wouldn't take much more to square up the sine wave
out of the opam and drop a cmos decade-divider onto that output of the
opamp and feed an ear phone with the dividers output--30,000 becomes
3,000 hz--easily "hear-able!"

only if theres no other sound present in the mic signal.

and it will give no indication of signal amplitude.

On Sat, 10 Mar 2007 09:19:25 -0500, PeterD wrote:
Why worry about it... His yard, his pets, his life...

I *think* what the OP is worried about is that his friends' pets are being
scared off by his freinds' neighbor.

While I hate to discourage anyone from building something electronic, I do
have to ask: what will one do if they learn that a bird-scarer *is* in
use? Best of my knowledge, they aren't illegal.

If a bird-scarer works on dogs, then I find the details quite interesting.
May have to work up a mobile version. Loose dogs allowed to roam a
neighborhood are a serious safety issue for cyclists. (and I wonder if
that's why the neighbor in question is trying to scare them off?)

clifto wrote:

John Smith I wrote:
Scott wrote:
clifto wrote:
Stace MacGuyver wrote:
Suspend a thin shaving razor blade between two pieces of dental floss
and put
your ear close to the blade. Watch the razor vibrate.

That's pretty cool, MacGuyver. Does the razor blade do anything?

It cuts off your ear if you get too close

Be better if you could use it as an electric razor ...

Replace the dental floss with Litz wire and attach ends to 110 VAC.

Wait. Maybe not. Considering how many stations you can pick up with a
razor-blade radio, that would probably interfere with vital communications
all throughout the spectrum. What's the resonant frequency of a whisker?


They don't make the blue blades anymore.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote:
clifto wrote:
John Smith I wrote:
Scott wrote:
clifto wrote:
Stace MacGuyver wrote:
Suspend a thin shaving razor blade between two pieces of dental floss
and put
your ear close to the blade. Watch the razor vibrate.

That's pretty cool, MacGuyver. Does the razor blade do anything?

It cuts off your ear if you get too close

Be better if you could use it as an electric razor ...

Replace the dental floss with Litz wire and attach ends to 110 VAC.

Wait. Maybe not. Considering how many stations you can pick up with a
razor-blade radio, that would probably interfere with vital communications
all throughout the spectrum. What's the resonant frequency of a whisker?


They don't make the blue blades anymore.

Do they make any other kind of thin shaving razor blades?

--
Martians drive SUVs! http://oregonmag.com/MarsWarm307.html

clifto wrote:

Michael A. Terrell wrote:
clifto wrote:
John Smith I wrote:
Scott wrote:
clifto wrote:
Stace MacGuyver wrote:
Suspend a thin shaving razor blade between two pieces of dental floss
and put
your ear close to the blade. Watch the razor vibrate.

That's pretty cool, MacGuyver. Does the razor blade do anything?

It cuts off your ear if you get too close

Be better if you could use it as an electric razor ...

Replace the dental floss with Litz wire and attach ends to 110 VAC.

Wait. Maybe not. Considering how many stations you can pick up with a
razor-blade radio, that would probably interfere with vital communications
all throughout the spectrum. What's the resonant frequency of a whisker?


They don't make the blue blades anymore.

Do they make any other kind of thin shaving razor blades?


Yes, but the blueing was what made a detector.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida