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Old 19th November 2004, 12:56 PM   #1
polsol is offline polsol  South Africa
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Default Lasers for security system

Sorry, this is pretty much off topic in terms of audio but has anyone any knowledge on where to purchase lasers and detectors for security systems?
The only lasers I seem to find on searching are the high power types costing big money or 'assembled' laser security systems.
Can't even seem to locate lasers for CD/DVD (I mean by accident whilst searching).
Any idea who manufactures/supplies lasers of this ilk?
As a side issue, most (all?) lasers are damaging to the eyes so how does one get past this problem?
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Old 21st November 2004, 09:54 PM   #2
imix500 is offline imix500  United States
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If you must have visible light just about any laser diode will do. You can find them at tons of surplus outlets online as well as ebay. Then all you need is a collimator to shrink the beam down and a photodiode. Most commercial units now use IR leds and detectors. They're a whole lot easier to deal with. Not all lasers will damage your eyes. Under the right conditions the laser diodes in cd players etc can cause some discomfort, but you literally have to stare into it for hours for it to have any effect. That's why CDRH has class ratings for lasers. Anything below class IIa isn't much of a problem. CD players etc mostly use class I to class II.
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Old 21st November 2004, 09:58 PM   #3
Magura is offline Magura  Denmark
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Hmm, would a simple laser ripped from a laserpointer do the trick?

Those are cheap and common.

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Old 22nd November 2004, 03:56 AM   #4
imix500 is offline imix500  United States
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Sure, but they are usually infared lasers. The laser diode will require a small power supply, which are redily available and easy to build. You will still need a collimator as the focal length will be much longer than that of inside the laser printer. On the plus side you can use a non sensitive IR photo diode or transistor with a strong source of light like that one and avoid false triggering from other light sources.
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Old 22nd November 2004, 10:40 AM   #5
polsol is offline polsol  South Africa
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Thanks for the help imix500.
What I forgot to mention (stupid of me!) is that I want to use the unit outdoors so there must be some means of filtering out the effects of sunlight. internal sensors are not just good enough as one of the problems is that many cases of theft are just smash and grab.
In January I was robbed twice within 24 hours whilst I and the family were away on a very rare holiday - even though I have an internal security system and 'rapid response' armed guards (via both remote telephone and radio alerts). It's what we have to live with in SA these days!
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Old 23rd November 2004, 02:28 AM   #6
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I wouldn't bother with lasers unless you're trying to get a beam to go 100m or so. Use a narrow angle IR led. Pulse it really hard (most can take 500mA pulses - check the data sheets). Pulsing gives you modulation, demodulating the receiver gives you back your signal - and immunity to sunlight, as long as your sunlight doesn't saturate the receiver.

You will still need focussing optics to go 5m or more - a couple of simple lenses should be sufficient.
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