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Need an infrared Laser pointer to be used to trigger an alarm

B

Bob Robertson

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This is my first post, and I am happy to have found a forum dedicated to this topic!

I will list the criteria I need to be able to meet below and hopefully someone here will have some advice for me and be able to tell me where to go. (in a good way)

This isn't actually going to be used as an alarm, but the concept is the same. It is really for a Halloween walktrough haunted trail I worked on this year. We need to have beams that can be broken when group walks by which would then trigger a particular special effect. I am good with the circuits that will accept the trigger and block it from being re-triggered for a per-determined amount of time, but I am having trouble finding a laser that I can use to make the beam that does what I need and doesn't break the bank.

Here's what I need:


I need an invisible light infrared (as close to 940nm as possible) laser pointer that can be used as a trigger switch for an alarm.

It has to be invisible to the eye.

It has to be able to be on continuously for many hours at a time (6 to 8 hours of continuous operation)

I do not need or want a beam that will burn things, just something to trigger a switch.

I hope to use the following phototransistor as a sensor that can tell if the beam has been broken: Infrared Phototransistors

I see that the phototransistor that I am looking at has a peak wavelength of 940nm. I am guessing that it will still see 980nm which is much more common. If not, I will look for a receiver set to 980.

So basically, I need a tripwire alarm using invisible light and want to know if anyone here knows where I can find something I can use for that purpose. The laser pointer would be approximately 10 feet away from the receiver.

Thank you for your help!
Bob
 





No, it needs to be a laser. There are too many other things that would be moving around and those motion sensors are too fickle. It has to be breaking a beam at a very specific point. I am also not really tied to the 940nm wavelength. As it turns out, I can use any photocell with an IR laser. So I would actually prefer a higher wavelength as I can see a pointer at 940nm. It really should be above that into the truly invisible spectrum, not just near IR. The main thing is that it HAS to have a continuous duty cycle. Most of what I see is 45 seconds on / 15 seconds off. There MUST be an IR laser pointer that can run continuously out there somewhere.
 
That duty cycle is only really for those high powered ones. The 1mw ones don't really produce much heat and are your best shot at extremely long duty cycles
 
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That's good. I don't need a high powered one. Nothing over 5mW. Trouble is, I can't find anything that is in the true IR range - Nearing 1000nm. 980 would probably due, although I can still see a slight glow while looking at the LEDs in that wavelength, but it wouldn't be obvious. Where can I find such a thing? So I'm looking for a 980nm wavelength laser pointer with an output power of 5mW or less that can be on continuously. I question the duty cycle becuase even 5mW units (Like this one: 980P 100 BL 980nm 5mW IR Infra Red Laser Pointer Pen | eBay) still have a short duty cycle in their specs.
 
At 5mW or less, I would think it would be very difficult to see 980nm for someone with good eyes and looking for it. An average person, with their attention focused on the creepy stuff around them, i highly doubt they would notice it.
 
Then I'm fine with that, but I still can't find any for sale anywhere, except for the one I listed which has a stupid duty cycle. Does anyone know where I can actually buy one?

I had no idea this would be so hard to find.

Thanks,
Bob
 
Thank you! That looks good. AixiZ has a good variety at great prices. I don't see any problem with their 5mW version. It does not list a limited duty cycle like the laser pointer I referenced. I will buy the 5mW version and try it out. Thanks again. That was the information I was looking for.
 
The problem with the 5mW version is that
980nm is almost completely invisible. If
someone happens to stare into it for long
enough, 5mW will still cause eye damage.
Even 1mW can cause eye damage. Buy the
lowest power that you can reasonably get
away with.
 
This will be mounted about 6 inches off the ground. Someone would have to try really hard to get it in the eye. The beam is meant to be broken by people's feet. I don't think that will be a problem.

Thanks for pointing out that potential problem, however.
 
you could buy a small DPSS low power 1064 nm module. I've seen them around. many are rated for about 25mW, but with a good heatsink, and a driver at a lower operating currenty you could under drive it a bit and it would be safe, focus adjustable (easier to aim at your sensor) and low power, and totally invisible, and still leave a small footprint. I think DealXtreme has some for like 5 bucks...
 
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