ideas for detecting a laser spot

[Ahmed Samir]

Hi everyone,
i am looking for a way to detect a laser pointer spot on incident on an area
of 0.25 square feet, the laser comes for ordinary laser pointers, from a
disstance like 50 feet or something.
any ideas??
thanks
ahmed samir

 

[Gary Lecomte]

"Ahmed Samir" <ahmdsamir.remove.SPAM@link.net> wrote in message news:<c16cqi$1e758v$1@ID-36824.news.uni-berlin.de>...

Hi everyone,
i am looking for a way to detect a laser pointer spot on incident on an area
of 0.25 square feet, the laser comes for ordinary laser pointers, from a
disstance like 50 feet or something.
any ideas??
thanks
ahmed samir

Go to my website at: http://www3.telus.net/chemelec/Projects/Projects.htm

There is a Laser Alarm circuit there that has a detector.

Take care.........Gary

 

[William J. Beaty]

"Ahmed Samir" <ahmdsamir.remove.SPAM@link.net> wrote in message news:<c16cqi$1e758v$1@ID-36824.news.uni-berlin.de>...

Hi everyone,
i am looking for a way to detect a laser pointer spot on incident on an area
of 0.25 square feet, the laser comes for ordinary laser pointers, from a
disstance like 50 feet or something.
any ideas??

Detecting YOUR laser pointer? Or ANY laser pointer?

Things become much easier if you chop the laser's power supply
at a couple of kilohertz or so, so the light is modulated.
Also, use very brief pulses with high power, maybe 50 uSec
or so, so the average power remains low even though the pulses
are very bright. These are well known tricks in the industrial
photosensors industry.

Second, if you know the laser wavelength, then you can put a
narrow-band filter on your photosensor. This lets you reject
all sorts of other light sources but without interfering
with the desired laser signal. If the photosensor sees darkness
with red laser spots, then you can crank the gain way up
without it being overloaded by room light, etc.

Of course if you're trying to detect laser pointers in general,
then all of the above is useless, since normal laser pointers
are DC, and normal laser pointers don't all have the same
wavelength. (Perhaps a red bandpass filter on the sensor would
help though. Just don't use an extremely narrow filter chosen
to pass only a particular laser wavelength.)


(((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://amasci.com
EE/programmer/sci-exhibits amateur science, hobby projects, sci fair
Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci

 

[CFoley1064]

Subject: ideas for detecting a laser spot
From: "Ahmed Samir" ahmdsamir.remove.SPAM@link.net
Date: 2/19/2004 6:51 PM Central Standard Time
Message-id: <c16cqi$1e758v$1@ID-36824.news.uni-berlin.de

Hi everyone,
i am looking for a way to detect a laser pointer spot on incident on an area
of 0.25 square feet, the laser comes for ordinary laser pointers, from a
disstance like 50 feet or something.
any ideas??
thanks
ahmed samir

If it's a low power visible red laser like most pointers, you might want to try
setting a photoresistor at the focal point of a fairly big lens, and measure
the change in resistance. Photoresistors have a response curve similar to that
of the eye, so if you can see it, you can probably get a response.

Good luck
Chris