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'[EE]: Again a laser discussion'
2001\02\01@072558 by Jinx

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> I read the circuit cellulars paper. Is there another web side
> regarding laser billboards?

There are quite a few to be found if you search for "laser
billboards" Most of them seem to be commercial sites, possibly
amateurs have them on the web by other names. Just keep
trying combinations of words

> Can sombody give me numbers about the response of
> the human visual system how fast the mirrors must turn?

The lasers that commercial operators use are many watts, and
as you'll have read in the CC paper, there's a trade-off between
the complexity of the display and how long it takes to refresh
and the dilution of the laser as you try to draw complex shapes.
You could probably display a simple shape (circle, sine) with
something like a safe low-power (mW) laser pointer at a relatively
slow speed without the display fading to badly. This is what is
going to determine the mirror operation - how complex the display
is and how long it takes to refresh it. As for eye response, the size
of the display (and the above) will most likely be the important factors.
I think you'll have to judge this by experimentation. Take a look at
this page

http://laseranimation.com/news/ne_frnews_e.html

for specs on a commercial set-up. It's a whole different ball
game, but you need that sort of horsepower for what their
customers (you and me at concerts etc) want

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2001\02\01@130410 by mike

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On Fri, 2 Feb 2001 01:27:05 +1300, you wrote:

{Quote hidden}

If you can find an old Philips top-loading laservision player, these
had a nice he-ne laser, and a neat 2-axis voice-coil mirror actuator
assembly. Ideal for displaying pretty patterns, especially
lissajous-type circular shapes, but won't move fast enough to do text
etc.
Last time I looked, the pros used very expensive galvanometer devices,
driven hard (& requiring extensive damage protection) for beam
scanning.    
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2001\02\02@035448 by Vasile Surducan

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Joe!

I'm interested if one of your laser printers ( from basement ) have a good
scanner. I need to know if in scanner is a visible laser diode or infrared
one. All my printers have deffective scanner ( error 52 or service 52
displayed...)
I've guess for a nice wall scope display a few mW are enough.
Comercial laser pointer have about 2...3mW and if are powered with 9V
instead of 3V have a nice spot ( and a short life of course )
Vasile




On Fri, 2 Feb 2001, Jinx wrote:

{Quote hidden}

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2001\02\02@051358 by Jinx

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>
> I'm interested if one of your laser printers ( from basement ) have
> a good scanner. I need to know if in scanner is a visible laser diode
> or infrared one. All my printers have deffective scanner ( error 52
> or service 52

Sadly, Vasile, mine are all either LED class or IR lasers. I thought
about that after our little chat off-list the other day. I couldn't make
a laser billboard or whatever with what I know to have here. Like
those motorised mirrors though, flippin' 'eck, don't they go !!!

Is there any common equipment that has red lasers in, apart from
laser tag games and pointers ? Are the blue (?) lasers in CD players
of any use for distance-type / measurement things ? Has anyone put
them to any other use ?

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2001\02\02@064132 by mike

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On Fri, 2 Feb 2001 23:16:11 +1300, you wrote:

>>
>> I'm interested if one of your laser printers ( from basement ) have
>> a good scanner. I need to know if in scanner is a visible laser diode
>> or infrared one. All my printers have deffective scanner ( error 52
>> or service 52
>
>Sadly, Vasile, mine are all either LED class or IR lasers. I thought
>about that after our little chat off-list the other day. I couldn't make
>a laser billboard or whatever with what I know to have here. Like
>those motorised mirrors though, flippin' 'eck, don't they go !!!
>
>Is there any common equipment that has red lasers in, apart from
>laser tag games and pointers ? Are the blue (?) lasers in CD players
>of any use for distance-type / measurement things ? Has anyone put
>them to any other use ?
Bar-code readers, although the handleld ones tend to use CCD sensors
and LED illumination nowadays.

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2001\02\02@065612 by Roman Black

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Jinx wrote:

> Is there any common equipment that has red lasers in, apart from
> laser tag games and pointers ? Are the blue (?) lasers in CD players
> of any use for distance-type / measurement things ? Has anyone put
> them to any other use ?

Most of those laser pointers sold as legal 1mW units
are actually 5mW units that can be operated at 5mW
(quite bright!!) if you ensure that their metal
collimator/heatsink thingy is reasonably cool.

CD lasers use near-IR, very low visibility and
high risk of eye damage. I've never seen a blue
semiconductor laser, even blue leds are very new
and possibly unstable.
-Roman

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2001\02\02@075201 by Vasile Surducan

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On Fri, 2 Feb 2001, Roman Black wrote:

> Jinx wrote:
>
> > Is there any common equipment that has red lasers in, apart from
> > laser tag games and pointers ? Are the blue (?) lasers in CD players
> > of any use for distance-type / measurement things ? Has anyone put
> > them to any other use ?
>
> Most of those laser pointers sold as legal 1mW units
> are actually 5mW units that can be operated at 5mW
> (quite bright!!) if you ensure that their metal
> collimator/heatsink thingy is reasonably cool.
>
> CD lasers use near-IR, very low visibility and
> high risk of eye damage. I've never seen a blue
> semiconductor laser, even blue leds are very new
> and possibly unstable.



 Blue led's are OK but have a voltage across junction three times largest
then red one. I've guess there are more then one junction inside.
I've playing with those and I don't saw any unstabilities after
more than 24 hours of continuous working in pulse mode.

 About laser pointers, I don't measure at any one more than 3mW
(measure not reading technical specifications ) output power.
( but here I have only russian pointers but russian laser's are known like
very good devices...)
Vasile

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2001\02\02@080204 by Jinx

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> CD lasers use near-IR, very low visibility and
> high risk of eye damage. I've never seen a blue
> semiconductor laser, even blue leds are very new
> and possibly unstable.
> -Roman

I'm pretty sure blue lasers are used now for some disk
reading because of the shorter wavelength and therefore
finer pits they can get into. There's some discussion about
what can be used for the next generation of finer resolution
of data media, similar to the one wrt microscopes

Thanks for the CD laser heads up. I've got some IR-sensitive
cameras - would they be harmed by low-power beams ? If I
do any work with these lasers a camera+monitor would seem
to be the safest way to view them

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2001\02\02@081037 by Roman Black

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Vasile Surducan wrote:
{Quote hidden}

How do you measure them Vasile? Mine were bought
from an associate who bought a big batch of them
from Asia as 5mW bright red. They are supposed to
be Russian ones. VERY bright!
-Roman

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2001\02\02@081457 by Roman Black

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Jinx wrote:

> I'm pretty sure blue lasers are used now for some disk
> reading because of the shorter wavelength and therefore
> finer pits they can get into. There's some discussion about
> what can be used for the next generation of finer resolution
> of data media, similar to the one wrt microscopes

Cool. Sounds expensive.


>
> Thanks for the CD laser heads up. I've got some IR-sensitive
> cameras - would they be harmed by low-power beams ? If I
> do any work with these lasers a camera+monitor would seem
> to be the safest way to view them

I don't think you will get a "beam" from a CD
laser, the lens makes a cone to a point. After
that they diffuse everywhere. Unless you have
some collimators from Oatley? I think they have
some near-IR lasers still. :o)

Can't say about the camera? I know my digital
camera sees the remote control led working.

-Roman

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2001\02\02@100457 by mike

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On Sat, 3 Feb 2001 02:03:14 +1300, you wrote:

>Thanks for the CD laser heads up. I've got some IR-sensitive
>cameras - would they be harmed by low-power beams ? If they are CCD or CMOS, no. It's possible that old vidicon tube type
cameras may suffer from 'burn-in' with small intense IR beams.
>If I do any work with these lasers a camera+monitor would seem
>to be the safest way to view them
Yes - this works very well.

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2001\02\02@100511 by mike

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On Sat, 3 Feb 2001 00:11:04 +1100, you wrote:

{Quote hidden}

If you can find a laser pointer with optics that can be dismantled
(usually older types), you may be able to transplant an IR laser diode
into it. Note however that the IR diode may well not work with the laser
pointer's power supply - the polarities of the laser and photodiode
are often different.
>Can't say about the camera? I know my digital
>camera sees the remote control led working.
Monochrome cameras work best. Colour ones have IR cut filters which
greatly attenuate IR, although you will probably still get enough
through to see it. Most colour cameras (often easier to find than mono) can be converted
for IR use -  you can often  dismantle the lens assembly and remove
the IR filter, which will be a light blue-green tinted.
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2001\02\02@152535 by Bob Blick

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> How do you measure them Vasile? Mine were bought
> from an associate who bought a big batch of them
> from Asia as 5mW bright red. They are supposed to
> be Russian ones. VERY bright!

Hi Roman,

5mW is a very standard maximum rating for the laser diodes typically used
in laser pointers. They work quite well at 5mW at reasonable temperatures
but don't last very long above that.

However, when the diode is putting out 5 mW, you will typically get only 2
or 3 mW out of the laser pointer, because the beam is usually clipped and
goes through uncoated optics. It's difficult not to clip the beam because
the output of laser diodes is an ugly fan-shape, quite unlike the
pencil-thin beam you associate with lasers. You have to put a collimating
lens in front of it, and building it all in a tiny pointer, you can't get
all the beam.

The reason these seemed so bright to you is the wavelength. A few years
ago laser pointers were 670-680 nM, a very dark red. Nowadays they are
more like 650 nM, and the eye is a lot more sensitive to it.

Cheerful regards,

Bob Blick

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2001\02\02@162229 by Jinx

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> Can't say about the camera? I know my digital
> camera sees the remote control led working.
>
> -Roman

Mine too, quick way of checking for working IR LEDs. Mike
Harrison's comments about IR lasers and cameras is
encouraging. Probably the laser wouldn't go straight into
the lens, I'd more likely be looking at a spot on the wall or
something. Just thought it wise to ask in case the lens ever
does catch the full beam, especially as IR lasers from say
printers etc seem to be a class more powerful than the red
pointer types (> 10mW ?)

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2001\02\02@173333 by Jinx

face picon face
> Monochrome cameras work best. Colour ones have IR cut
> filters which greatly attenuate IR, although you will probably
> still get enough through to see it.

The miniature (Oatley Roman !!) b/w cameras are very sensitive
to IR and output quite a different picture to the camcorder set to
b/w. For example they can "see" speakers behind grille cloth
and black fabrics that look identical in sunlight can show up as
anything from bright grey to black. The last practical use I had
for one was to find out which of the neighbourhood cats was
coming in the catflap at night and peeing on the stove elements.
Ever smelled roasting cat pee ? It was also rotting the metalwork.
Strange but true. Why any cat would want to claim our stove as
territory I have no idea.

But anyhoo, I set the VCR on LP and taped 8 hours of the top of
a stove night after night. The camera had a 1/2 dozen IR LEDs
for illumination, and I'm thinking you could probably use a scrap
IR laser + camera as a night scope, as a cheap alternative to a
photomultiplier

(found out which moggy it was btw, not our little darling, so we
changed to a smart catflap)

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2001\02\03@093301 by mike

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On Sat, 3 Feb 2001 11:35:04 +1300, you wrote:

>> Monochrome cameras work best. Colour ones have IR cut
>> filters which greatly attenuate IR, although you will probably
>> still get enough through to see it.
>
>The miniature (Oatley Roman !!) b/w cameras are very sensitive
>to IR and output quite a different picture to the camcorder set to
>b/w. For example they can "see" speakers behind grille cloth
>and black fabrics that look identical in sunlight can show up as
>anything from bright grey to black. The last practical use I had
>for one was to find out which of the neighbourhood cats was
>coming in the catflap at night and peeing on the stove elements.
>Ever smelled roasting cat pee ? It was also rotting the metalwork.
>Strange but true. Why any cat would want to claim our stove as
>territory I have no idea.
>
>But anyhoo, I set the VCR on LP and taped 8 hours of the top of
>a stove night after night. The camera had a 1/2 dozen IR LEDs
>for illumination, and I'm thinking you could probably use a scrap
>IR laser + camera as a night scope, as a cheap alternative to a
>photomultiplier
A torch with an IR filter, or a big bunch of IR LEDs would probably be
a lot more effective - lasers are less efficient than a few LEDs for
illuminating more than a spot.

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2001\02\04@022800 by Bill Westfield

face picon face
   5mW is a very standard maximum rating for the laser diodes typically used
   in laser pointers. They work quite well at 5mW at reasonable temperatures
   but don't last very long above that.

Um, how do you change the output power produced by one of those laser
diodes, anyway?  I thought they were all the sort where you essentially
detected output via the built-in photodiode, and didn't let the current
climb any higher than that?  Wouldn't that make the actual output wholely
dependent on the laser diode itself?

BillW

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2001\02\04@122155 by Bob Blick

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>Um, how do you change the output power produced by one of those laser
>diodes, anyway?  I thought they were all the sort where you essentially
>detected output via the built-in photodiode, and didn't let the current
>climb any higher than that?  Wouldn't that make the actual output wholely
>dependent on the laser diode itself?

Hi Bill,

You can have the monitor photodiode in the circuit as a feedback element,
and varying the load on it with a trimpot sets the output power. You also
have a current limit set to the maximum rated current, so when the
efficiency drops because of high temperature, you don't burn it out from
too much current in a vain attempt to maintain output power. If you adjust
the power real low, say under 1 mW, it looks a little noisy during the
first microsecond because the laser diode is so nonlinear there's no way
the frequency compensation in your circuit can match it. But as long as you
are running continuous wave you can pretty much adjust the output from
almost nothing to full.

You don't have to use the monitor photodiode, just drive the laser diode
with a constant current source, but the output varies with temperature, and
you need to drive it with enough current to reach the lasing threshold,
which can be very close to hurting the diode from too much optical power(if
you are at a lower temperature than you expected). In a pinch you can put a
low value(100 ohms) PTC thermistor in series with the diode and just ignore
the photodiode. But that would be wrong :-)

Cheerful regards,

Bob Blick

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2001\02\04@165722 by Tony Nixon

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Jinx wrote:

> (found out which moggy it was btw, not our little darling, so we
> changed to a smart catflap)

I would have changed the stove to gas with auto ignition.

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mICro's
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salesspamKILLspampicnpoke.com

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2001\02\04@201701 by Jinx

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> > (found out which moggy it was btw, not our little darling, so we
> > changed to a smart catflap)
>
> I would have changed the stove to gas with auto ignition.

We're waiting until the guilty party grows up and buys a stove
of its own. Then one night we sneak in...........

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2001\02\04@203548 by Jinx

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> > (found out which moggy it was btw, not our little darling, so we
> > changed to a smart catflap)
>
> I would have changed the stove to gas with auto ignition.
> Tony

That's how you get a cat to do dog impressions - WOOOOF !!!

(Which I'd never do to mine of course, much loved. He's not a
child-substitute you understand, or that's what his piano teacher
says)

To get a dog to do cat impressions you run it through a bandsaw -
miiiaaaaooooowwww !!!!

OK, I'm done ;-)

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2001\02\05@014532 by Vasile Surducan

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On Sat, 3 Feb 2001, Roman Black wrote:

{Quote hidden}

 I have here an energimeter for CW laser built by one of my collegue.
Some time ago we build such tools including ratiometer measurements.
The principle is to convert thermal result of radiation into an electrical
signal using a pyroelectric TGS crystal sprayed with graphyte.
It use a sample and hold tehnique for achieving results.
The major problem is: after a while the TGS who is a hygroscopic material,
becomes unusable and a new one must be recalibrated before use.
Vasile

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2001\02\05@052456 by Vasile Surducan

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On Sat, 3 Feb 2001, Jinx wrote:

> > Can't say about the camera? I know my digital
> > camera sees the remote control led working.
> >
> > -Roman
>
> Mine too, quick way of checking for working IR LEDs. Mike
> Harrison's comments about IR lasers and cameras is
> encouraging. Probably the laser wouldn't go straight into
> the lens, I'd more likely be looking at a spot on the wall or
> something. Just thought it wise to ask in case the lens ever
> does catch the full beam, especially as IR lasers from say
> printers etc seem to be a class more powerful than the red
> pointer types (> 10mW ?)
>
 A standard IR LED at 920 nm wavelenght at 25mA has between 6 and 9 mW
Is more powerfull but unfortunately is invisible and the spot it hasn't
a "point shape". I've built an infrared barrier in my garden, up to 15
meters distance between emiter and receiver using black plastic lenses,
infrared transparent. At 15 m dissipation of the spot is about 50cm !
The barrier detect the intruders and the snowflake too...
Vasile

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2001\02\05@053332 by Michael Rigby-Jones

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> -----Original Message-----
> From: William Chops Westfield [SMTP:RemoveMEbillwTakeThisOuTspamCISCO.COM]
> Sent: Sunday, February 04, 2001 7:28 AM
> To:   spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
> Subject:      Re: [EE]: Again a laser discussion
>
>     5mW is a very standard maximum rating for the laser diodes typically
> used
>     in laser pointers. They work quite well at 5mW at reasonable
> temperatures
>     but don't last very long above that.
>
> Um, how do you change the output power produced by one of those laser
> diodes, anyway?  I thought they were all the sort where you essentially
> detected output via the built-in photodiode, and didn't let the current
> climb any higher than that?  Wouldn't that make the actual output wholely
> dependent on the laser diode itself?
>
> BillW
>
Any control circuit has to have a reference!  The BFM (back facet monitor)
diode is essentialy the sense element in a control loop.  The current
through  this diode is compared to a reference and the resulting control
current to fed to the laser driver.

Mike

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2001\02\05@060136 by Jinx

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> A standard IR LED at 920 nm wavelenght at 25mA has
> between 6 and 9 mW Is more powerfull but unfortunately is
> invisible and the spot it hasn't a "point shape". I've built an
> infrared barrier in my garden, up to 15 meters distance
> between emiter and receiver using black  plastic lenses,
> infrared transparent. At 15 m dissipation of the spot is about
> 50cm ! The barrier detect the intruders and the snowflake too..
> Vasile

I see. And snowflakes are particularly dangerous in Romania ?
Winter must be hell for you with alarms going off every 0.1 seconds

Your lenses sound out of focus. My IR laser module has a spot
around 5cm wide at 12m. I was thinking of using it as a perimeter
detector like you've done but never got around to putting up the
mirrors for it to bounce around the fence line. I could use a red
laser if the beam arrived at and left the mirrors through tubes to
hide any illumination. Have you thought of using a line generator
to make a planar beam and flood the area ? I've got pics of
simple ones made from acrylic rod you could probably make

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2001\02\05@063111 by Vasile Surducan

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On Tue, 6 Feb 2001, Jinx wrote:

> > A standard IR LED at 920 nm wavelenght at 25mA has
> > between 6 and 9 mW Is more powerfull but unfortunately is
> > invisible and the spot it hasn't a "point shape". I've built an
> > infrared barrier in my garden, up to 15 meters distance
> > between emiter and receiver using black  plastic lenses,
> > infrared transparent. At 15 m dissipation of the spot is about
> > 50cm ! The barrier detect the intruders and the snowflake too..
> > Vasile
>
> I see. And snowflakes are particularly dangerous in Romania ?
> Winter must be hell for you with alarms going off every 0.1 seconds
>
 He, he ... Alarm is not active from 5 years, but the barrier is active
and switch on a LED... This winter it snows just two times.

> Your lenses sound out of focus. My IR laser module has a spot
> around 5cm wide at 12m. I was thinking of using it as a perimeter
> detector like you've done but never got around to putting up the
> mirrors for it to bounce around the fence line. I could use a red
> laser if the beam arrived at and left the mirrors through tubes to
> hide any illumination. Have you thought of using a line generator
> to make a planar beam and flood the area ? I've got pics of
> simple ones made from acrylic rod you could probably make


Lenses are very close to Fresnel style because are done on the lathe.
I think polishing surface may improve quality.
About the planar beam send me the pictures and go to sleep Joe ( or
finalise your "sheep site")
By, Vasile

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2001\02\05@064349 by Jinx

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> > I see. And snowflakes are particularly dangerous in Romania ?
> > Winter must be hell for you with alarms going off every 0.1
> > seconds
>
>   He, he ... Alarm is not active from 5 years, but the barrier is
> active and switch on a LED... This winter it snows just two times.

Ah OK, no need then to move to a country like Tonga which has a
low snowflake infestation index

>  Lenses are very close to Fresnel style because are done on the
> lathe. I think polishing surface may improve quality.

> About the planar beam send me the pictures and go to sleep Joe
> ( or finalise your "sheep site")
> By, Vasile

I will, I will, I will (in no particular order). As you've got access to a
lathe I don't think these will be a big job

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2001\02\05@070044 by Roman Black

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Vasile Surducan wrote:

> > How do you measure them Vasile? Mine were bought
> > from an associate who bought a big batch of them
> > from Asia as 5mW bright red. They are supposed to
> > be Russian ones. VERY bright!
> > -Roman
> >
>   I have here an energimeter for CW laser built by one of my collegue.
> Some time ago we build such tools including ratiometer measurements.
> The principle is to convert thermal result of radiation into an electrical
> signal using a pyroelectric TGS crystal sprayed with graphyte.
> It use a sample and hold tehnique for achieving results.
> The major problem is: after a while the TGS who is a hygroscopic material,
> becomes unusable and a new one must be recalibrated before use.
> Vasile


Thank you Vasile. Sounds like nice equipment! :o)
Shame I can't use that to measure mine... Oh well...
-Roman

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2001\02\05@075107 by Vasile Surducan

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On Fri, 2 Feb 2001, Bob Blick wrote:

{Quote hidden}

 My wavelenght measurement is  very close with your information Bob !
Unfortunately my monochromator has a 10nm bandwith so acurracy is +/-10nM
For these laser pointers I've got a dispersion beetwen 630 to 660 nm.
Congratulations for your amazing propeller clock !
Vasile

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2001\02\05@102457 by goflo

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Jinx wrote:
> > > (found out which moggy it was btw, not our little darling, so we
> > > changed to a smart catflap)

> > I would have changed the stove to gas with auto ignition.

> We're waiting until the guilty party grows up and buys a stove
> of its own. Then one night we sneak in...........

It is written: "Don't piss on B+."
Suggests an alternative approach...

Jack

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2001\02\05@173957 by Mike Mansheim

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>> changed to a smart catflap)

What is a *smart* catflap?? (pic powered?)

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2001\02\05@175620 by Chris Carr

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> >> changed to a smart catflap)
>
> What is a *smart* catflap?? (pic powered?)
>
Yes, You use the Microchip RFID products

(Not Laser)    8-)

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2001\02\05@222613 by Jinx

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> What is a *smart* catflap?? (pic powered?)

Magnetic

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2001\02\06@013345 by artstar

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Superglued 3#-)


Adios,
LarZ

---------------  TAMA - The Strongest Name in Drums  ---------------

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