jsimpson001
Member
has anyone ever made a laser beam alarm, and what type of detector should I use?
Laser beam alarm for doorway...
- Thread starter jsimpson001
- Start date
Rickharris
Senior Member
Even better normal light - you still can't see it in clean air.
detector an LDR (Light Dependent Resistor)
detector an LDR (Light Dependent Resistor)
jsimpson001
Member
hi xstamp, Yeah i suppose it would be safer as well, but IR doesnt have such a good range, especially when bounced around a doorway with mirrors, lasers have effecively infinite range because the light rays are in phase with each other. have you seen an IR emitter with a couple of meters range on it. I breadboarded an IR circuit but the max range was only a few centimetres (using a TSOP48-type receiver and emitter modulated at 38khz(pwmout)
Edited by - jsimpson001 on 04/02/2007 19:53:21
Edited by - jsimpson001 on 04/02/2007 19:53:21
jsimpson001
Member
Hi Rickharris, the problem ive got with normal light is the 'interference' when someone switches a light on (and these cn be easily jammed with a torch 
That is precisely why 'proper' break beams are modulated, with a bit of fancy stuff at the receiver. This has been around for donkey's years.
There is no reaon why a normal I/R LED shouldn't give a couple of metres at the very least. An LED plus good lens could give loads of metres - though aligment gets trickier.
Some years ago I designed an infra-red detector which bounced the I/R off people and detected the return signal.
This had a range of over 4 metres in >60000 lux daylight even if the person was wearing a white T-shirt. It used an OD880W I/R LED pulsed at up to 3 amps and 30mm lenses. The signal to noise was terrible but that TBA2800 was a fantastic ic. (And, my lens / baffle design was pretty good even if I say so myself.)
A similar setup using a modest SFH485 I/R LED + 30mm lenses gave me a break-beam detector capable of over 30 metres easily in bright daylight - though the slightest wobble messed it up.
That was a very long and boring story to tell you that laser is NOT the answer for everything. And that it is up to you to produce a cunning design.
And another thing for break-beam; bugs.
If you use lenses on Tx and Rx, you will have an effective beam diameter (I know... let's not nitpick) the same diameter as the lens. Laser will obv be very narrow. This makes bluebottles and slight wobbles less likely to trigger your detector - assuming its been thoughtfully designed . (yeah yeah multi-beams, optics, blah blah) but you get my drift?
Laser safety. Absolutley. Esp I/R lasers which you can't see. I have been waitng (for over a year) for a reply on laser safety from the UK HSE about modulated laser safety. I asked (three times) , would 1% duty on a 3mW I/R laser be deemed safe. No reply, so another project moved to back of drawer.
There is no reaon why a normal I/R LED shouldn't give a couple of metres at the very least. An LED plus good lens could give loads of metres - though aligment gets trickier.
Some years ago I designed an infra-red detector which bounced the I/R off people and detected the return signal.
This had a range of over 4 metres in >60000 lux daylight even if the person was wearing a white T-shirt. It used an OD880W I/R LED pulsed at up to 3 amps and 30mm lenses. The signal to noise was terrible but that TBA2800 was a fantastic ic. (And, my lens / baffle design was pretty good even if I say so myself.)
A similar setup using a modest SFH485 I/R LED + 30mm lenses gave me a break-beam detector capable of over 30 metres easily in bright daylight - though the slightest wobble messed it up.
That was a very long and boring story to tell you that laser is NOT the answer for everything. And that it is up to you to produce a cunning design.
And another thing for break-beam; bugs.
If you use lenses on Tx and Rx, you will have an effective beam diameter (I know... let's not nitpick) the same diameter as the lens. Laser will obv be very narrow. This makes bluebottles and slight wobbles less likely to trigger your detector - assuming its been thoughtfully designed . (yeah yeah multi-beams, optics, blah blah) but you get my drift?
Laser safety. Absolutley. Esp I/R lasers which you can't see. I have been waitng (for over a year) for a reply on laser safety from the UK HSE about modulated laser safety. I asked (three times) , would 1% duty on a 3mW I/R laser be deemed safe. No reply, so another project moved to back of drawer.
jsimpson001
Member
As an alternative to this idea, Dippy, I could fix the device (alarm) to a door and have the IR receiver and emitter pointing at the (gloss painted) doorframe, the only disadvantage is that the door would have to remain closed...
hippy
Ex-Staff (retired)
<i>have you seen an IR emitter with a couple of meters range on it </i>
Plenty; just tested my Sky Satellite receiver and that detected the handset up to 15m before I ran out of backing-up space. I also keep my H-Fi and AV kit tucked in an alcove and bounce the IR off the opposite wall to control them.
Plenty; just tested my Sky Satellite receiver and that detected the handset up to 15m before I ran out of backing-up space. I also keep my H-Fi and AV kit tucked in an alcove and bounce the IR off the opposite wall to control them.
jsimpson001
Member
Im going to give Dippy's lens idea a go, witha 4x20 air rifle sight.
toxicmouse
Senior Member
lasers are very effective if you want a long beam, i have cannibalised a small toy laser and used a phototransistor. i managed to get a 30m reliable beam, just using comparators. separately i used the same arangement in an outdoor application where a simple on/off was required, and that also worked. the biggest problem is the allignment.
the phototransistor was a SFH309, made by Siemens. available at Maplins (UK) code CY86T for under £1.
I am sure the concerns about lasers are justified, but I doubt the cheap toy lasers are much of a hazard.
the phototransistor was a SFH309, made by Siemens. available at Maplins (UK) code CY86T for under £1.
I am sure the concerns about lasers are justified, but I doubt the cheap toy lasers are much of a hazard.
Oh, toxicmouse. You shouldna said that.
You'll start 3 pages of tales of doom...
The Target Reflective (or Retro reflective) method is not easy. Our method measured the received integrated pulse charge levels from 10uS pulse trains and used a processor for comparisons. Sorry, I'm not trying to sound flash - just pointing out that it wasn't easy.
Just get a good acrylic lens. Pop one out of a GOOD quality 'jewellers loupe' type eyepiece. CTP-COIL made superb lenses. The baffling to prevent extraneous light (esp if used outdoors) is crucial - check out the insides of a telescope. Good luck.
On the subject of reflective break-beam alarms; gloss paint.
Do be aware that people will reflect I/R. Therefore someone may pass through without apparently breaking the beam. However, 1998 black jeans from Marks & Spencers are fantastic near I/R absorbers.
Edited by - Dippy on 04/02/2007 22:50:25
You'll start 3 pages of tales of doom...
The Target Reflective (or Retro reflective) method is not easy. Our method measured the received integrated pulse charge levels from 10uS pulse trains and used a processor for comparisons. Sorry, I'm not trying to sound flash - just pointing out that it wasn't easy.
Just get a good acrylic lens. Pop one out of a GOOD quality 'jewellers loupe' type eyepiece. CTP-COIL made superb lenses. The baffling to prevent extraneous light (esp if used outdoors) is crucial - check out the insides of a telescope. Good luck.
On the subject of reflective break-beam alarms; gloss paint.
Do be aware that people will reflect I/R. Therefore someone may pass through without apparently breaking the beam. However, 1998 black jeans from Marks & Spencers are fantastic near I/R absorbers.
Edited by - Dippy on 04/02/2007 22:50:25
hippy
Ex-Staff (retired)
No need for pages of doom, when there's plenty of evidence already available. One of the problems is that people keep treating these things as "toys" when they are no such thing - <A href='http://vision.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=vision&cdn=health&tm=54&f=00&su=p284.5.420.ip_&tt=2&bt=1&bts=1&zu=http%3A//www.uni-duesseldorf.de/WWW/MedFak/LaserMedizin/hering/laserpointer/laserpointer_engl.html' Target=_Blank>External Web Link</a>
<i>Given the current situation, where lasers have become small and easy to use and are being sold at favourable prices to private individuals, it is probably high time that the regulations governing such lasers were revised. One thing is certain - there should be a ban on selling such lasers to children and youngsters, because they are the very ones who have no idea at all of how dangerous such devices are </i>
I wholeheartedly agree.
<i>Given the current situation, where lasers have become small and easy to use and are being sold at favourable prices to private individuals, it is probably high time that the regulations governing such lasers were revised. One thing is certain - there should be a ban on selling such lasers to children and youngsters, because they are the very ones who have no idea at all of how dangerous such devices are </i>
I wholeheartedly agree.
Also agreed- aside from cricket & soccer match nightmares,bored kids can play with lasers while travelling. I've just finished a LONG hot summery NZ late night drive, & at one stage was behind a car whose rear passengers zapped me with a laser pointer. Doubt if their driver ever knew what caused the resulting fist shaking. Yes- I got their rego., but ...
Well , I'm certainly not poo-pooing safety aspects. Eye damage can be irreversible. And it doesn't help that the flood of cheap Chinese imports is (basically) unregulated with labelling being questionable.
Children should not have them, nor should thick adults.
But, for intelligent users, let's not panic; we can all find links that 'prove' a theory (one way or the other):-
<A href='http://bjo.bmj.com/cgi/content/full/83/10/1164' Target=_Blank>External Web Link</a>
And as I am the world's greatest cynic and I hear of a school bus driver, who is suing because of serious eye damage caused by a brief glimpse of a laser in his rear-view-mirror, I cry 'compensation culture'!! As difficult to disprove as back-ache.
Have a look at this:-
<A href='http://vision.about.com/od/eyesafety/a/laserpointereye.htm' Target=_Blank>External Web Link</a>
60 of seconds of green laser.
Say, do you go blind when you glimpse the red laser at shop checkouts? Let's not confuse 'dazzle' with 'damage'.
Let's NOT be blase (pronounced blarzay) but lets not panic.
But, on the other hand, let's be careful and sensible.
And as for little ****s waving lenses into drivers eyes, they should be punished. Dazzling, distracting and downright dangerous.
Report them Stan.
Edited by - Dippy on 06/02/2007 12:13:23
Children should not have them, nor should thick adults.
But, for intelligent users, let's not panic; we can all find links that 'prove' a theory (one way or the other):-
<A href='http://bjo.bmj.com/cgi/content/full/83/10/1164' Target=_Blank>External Web Link</a>
And as I am the world's greatest cynic and I hear of a school bus driver, who is suing because of serious eye damage caused by a brief glimpse of a laser in his rear-view-mirror, I cry 'compensation culture'!! As difficult to disprove as back-ache.
Have a look at this:-
<A href='http://vision.about.com/od/eyesafety/a/laserpointereye.htm' Target=_Blank>External Web Link</a>
60 of seconds of green laser.
Say, do you go blind when you glimpse the red laser at shop checkouts? Let's not confuse 'dazzle' with 'damage'.
Let's NOT be blase (pronounced blarzay) but lets not panic.
But, on the other hand, let's be careful and sensible.
And as for little ****s waving lenses into drivers eyes, they should be punished. Dazzling, distracting and downright dangerous.
Report them Stan.
Edited by - Dippy on 06/02/2007 12:13:23