Re: [NYCR:Microcontrollers] Is an eye safe laser trip wire possible?

[Eric Skiff]

In my experience, IR range finders have a pretty narrow field of view, although I'm sure they vary a bit. If you were to put one in a doorframe aimed at the other side, you'd certainly know when someone went through the door, and that would be my pick for this project unless you need the "tripwire" to go a long distance (say across an entire room). 

As far as lasers, low-power lasers should be detectable but safe to use. Under 5mw lasers (5mw is the limit for handhelp pointers, etc, in the US) theoretically shouldn't do any damage to the retina before someone's blink reflex protects them, but i'd say the lower power the better. 

-Eric

On Thu, May 24, 2012 at 9:55 AM, luke browngold <victo...@gmail.com> wrote:

I need to create a laser trip wire. Usually I would just do something like this http://www.instructables.com/id/Arduino-Laser-Tripwire/. The only problem is that this laser needs to be at eye level and I would prefer not to blind anyone. Is there anyway I can set something like this up that uses an invisible form of light? It seems that there are some toys that do it http://www.youtube.com/watch?v=7AyeyE6_v5U? Does  anyone know what this type of laser is called?

I also consider ultrasonic and ir range finders but the "trigger" area needs to be very responsive, small and focused.

I also thought about using a PIR Motion Sensor and putting it in a cardboard tube to limit the trigger area. Has anyone ever tried this?

Thanks,

~luke

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[Guan Yang]

Will the blink reflex also react to infrared lasers?

On Thursday, May 24, 2012 at 10:26 , Eric Skiff wrote:

> In my experience, IR range finders have a pretty narrow field of view, although I'm sure they vary a bit. If you were to put one in a doorframe aimed at the other side, you'd certainly know when someone went through the door, and that would be my pick for this project unless you need the "tripwire" to go a long distance (say across an entire room).
>
> As far as lasers, low-power lasers should be detectable but safe to use. Under 5mw lasers (5mw is the limit for handhelp pointers, etc, in the US) theoretically shouldn't do any damage to the retina before someone's blink reflex protects them, but i'd say the lower power the better.
>
> -Eric
>

> On Thu, May 24, 2012 at 9:55 AM, luke browngold <victo...@gmail.com (mailto:victo...@gmail.com)> wrote:
> > I need to create a laser trip wire. Usually I would just do something like this http://www.instructables.com/id/Arduino-Laser-Tripwire/. The only problem is that this laser needs to be at eye level and I would prefer not to blind anyone. Is there anyway I can set something like this up that uses an invisible form of light? It seems that there are some toys that do it http://www.youtube.com/watch?v=7AyeyE6_v5U? Does anyone know what this type of laser is called?
> >
> > I also consider ultrasonic and ir range finders but the "trigger" area needs to be very responsive, small and focused.
> >
> > I also thought about using a PIR Motion Sensor and putting it in a cardboard tube to limit the trigger area. Has anyone ever tried this?
> >
> > Thanks,
> > ~luke
> >
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[luke browngold]

[Alpay Kasal]

an IR laser under 5mw is legal and safe to operate without a special license or protection.

You should also be aware of this, <5mw has a good chance of getting blown out by ambient IR in a well lit room during daylight. If you are in an environment with any daylight, I'd DEFINITELY go for a ping sensor (or other ultrasonic) connected to a microcontroller. This will not be affected by lighting conditions, and acts just like a trip wire. it is a straight beam of inaudable sound, it reports range of distance. I have used this in exactly the same way before, the beam coming out of a ping is like an invisible strand of string through the environment. it seems to be very accurate too. I needed resolution in inches but i think it will show differences in mm.

>but the "trigger" area needs to be very responsive, small and focused.

The ping sensor will give you this.

Alpay Kasal
Engineer
http://Supertou.ch
twitter: @alpaykasal
blog: http://blog.LitStudios.com

On Thu, 24 May 2012 10:26:29 -0400, Eric Skiff <m...@ericskiff.com> wrote:

In my experience, IR range finders have a pretty narrow field of view, although I'm sure they vary a bit. If you were to put one in a doorframe aimed at the other side, you'd certainly know when someone went through the door, and that would be my pick for this project unless you need the "tripwire" to go a long distance (say across an entire room). 

As far as lasers, low-power lasers should be detectable but safe to use. Under 5mw lasers (5mw is the limit for handhelp pointers, etc, in the US) theoretically shouldn't do any damage to the retina before someone's blink reflex protects them, but i'd say the lower power the better. 

-Eric

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[luke browngold]

Thanks Alpay, I always assumed these ultra sonice senors had a projected out "cone" trigger area. I will do more research. Do you have any particular sensor you are partial too?

~luke

[Dan Lavin]

These are easy to use:

http://www.maxbotix.com/products.htm#LV-EZ

However, I never was able to get the serial mode working.

[Alpay Kasal]

http://www.parallax.com/tabid/768/ProductID/92/Default.aspx

This is the one I have used the most, it is very line-of-sight. I believe it is also sold at Radio Shack.

Alpay Kasal
Engineer
http://Supertou.ch
twitter: @alpaykasal
blog: http://blog.LitStudios.com