On Tue, 13 Mar 2007 18:40:06 +0000, Michael A. Terrell wrote:
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.


I don't know how your sense organs are arranged, but I know that if I
dangle something next to my ear, it's terribly hard to watch it
simultaneously. ;-)



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.

What does that have to do with dangling the blade from dental floss? Or,
for that matter, what does dangling a blade from dental floss even DO?

Thanks,
RIch

On Mar 10, 9:18 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!

If you want to compress the range of 0-30 kHz to something like 0-12
kHz you can do that with a switched capacitor delay chip like the
Panasonic MN3007.

It will work like the bat detector, except it won't need to clip and
threshold the audio. You will need to use a slow ramped VCO
(continually ramping the sampling frequency down) in order to do this.
There are some projects at:
http://www.geofex.com/
You may be able to adapt a flanger, for instance, to suit your
purpose.

The control voltage to the sampling VCO will be a sawtooth wave.
Unfortunately, you will hear the sawtooth period as an artifact in the
output. Maybe you can filter it out.

I guess an all-digital solution is better ;-)

Frank Raffaeli

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.


Hmm. i was going to say, if it worked, it would be cutting edge
technology!


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Jamie 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.


Hmm. i was going to say, if it worked, it would be cutting edge
technology!

A sharp observation indeed.

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

On a sunny day (Tue, 13 Mar 2007 22:42:58 GMT) it happened Rich Grise
wrote in :

On Tue, 13 Mar 2007 18:40:06 +0000, Michael A. Terrell wrote:
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.


I don't know how your sense organs are arranged, but I know that if I
dangle something next to my ear, it's terribly hard to watch it
simultaneously. ;-)

Mirror, webcam, helper,

On Mar 11, 1:19 am, PeterD wrote:
On 10 Mar 2007 05:18:34 -0800,
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!

Why worry about it... His yard, his pets, his life...

OK,

Take a microphone with a frequency response 30Khz, and an amplifer.
Monitor the amp's output with a scope. bg

Agree. Even a bog standard electret for $1 will do it - probably
wouldn't even need an amplifier......if you want to get sophisticated,
put it in the end of a piece of 30mm plastic pipe - voila, directional
microphone....

The alternative is you are just being paranoid......but I know you
know that anyway...

Andrew VK3BFA.

Jamie wrote:

Michael A. Terrell wrote:

They don't make the blue blades anymore.

Hmm. i was going to say, if it worked, it would be cutting edge
technology!


It was, a millennium ago.

--
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

Do you know of any freq response curves on the web for the garden
variety electrets? I've looked and haven't found any.
====================
I found an Archer packaged (for Tandy) cat no 270-092B Electret
Condenser Mike Element in its original Package, complete with response
curve.
From 30 - 3000 Hz the response is flat.
From 3000 Hz to 5000 Hz the response increases by approx 10 dB.
From 5000 - 9000 Hz the response drops such that it is back to its
original level at 9000 Hz .Above that freq the response drops.
Response curve is not extended beyond 12000 Hz



Frank GM0CSZ / KN6WH

Andrew VK3BFA wrote:


Take a microphone with a frequency response 30Khz, and an amplifer.
Monitor the amp's output with a scope. bg

Agree. Even a bog standard electret for $1 will do it - probably
wouldn't even need an amplifier......if you want to get sophisticated,
put it in the end of a piece of 30mm plastic pipe - voila, directional
microphone....

The alternative is you are just being paranoid......but I know you
know that anyway...

Andrew VK3BFA.


Hello Andrew,

Do you know of any freq response curves on the web for the garden
variety electrets? I've looked and haven't found any.

Thanks,

Chuck NT3G

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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=B4t 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=B4s 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=B4ve
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!

Google for 'bat detector'.

--
Reply to nico@nctdevpuntnl (punt=.)
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