Laser Diodes and Target Switches

First, at the very least, you'll need to collimate the laser beam.

Second, what are you planning to use as a receiver?

Third, 5mW (@ 650nm) is pretty weak to be seen in daylight over 100 ft away. More than likely, the beam will be obscured by ambient light.

I kind of think that you need to rethink your design.

Not to mention that at 5mW or so it becomes a Class B (?) laser, and there are regulations and such for operating a laser at class B and above. I wouldn't doubt that someone in some govt. org wouldn't like this because of the possibility of 'burning' someone's eye out... I would suggest that some other type of system be used...

This would be used in bright daylight.

During testing we found that red laser diodes were practically invisible in bright sunlight even at short distances of around. If you want to be able to see the laser point on the target with the naked eye what you are going to need is a green laser diode. These work wonderfully in bright sunlight and are clearly visible on a paper target at around 80-90 ft.

As for electronically sensing, red or green lasers should be fine. Not sure what would be the best light sensor as it needs to have quite a narrow frequency band and natural light (which contains the red and green laser diode light frequencies) may overwelm the laser light giving constant false readings. This is one of the main reasons laser and light sensor target games are done in low light conditions.

You may need to pulse the laser to produce a coded light signal that the reciever can read (takes care of natural light causing false readings but not the problem of too much natural light overwelming the laser signal).

I look forward to a discussion and possible inexpensive solutions on this as I may also have an application where this may be useful.

I have an infrared targeting system I have designed that works out to 400 yards. Of course I'm driving a 25 watt laser to only about 5 watts and it is pulse coded so that many different codes are available. This is way over kill for what you need but in theory you could adapt it. If you want to read an article I wrote describing the basis for the technology you can check issue 179 June 2005 of Circuit Cellar Ink. It is just a matter of using the appropriate optics and electro-optics. The circuit described is very sensitive and operates indifferently to ambient lighting.

Maybe I am being too negative, but I cannot believe that this will ever work, the reasons are as follows:-

1) Each plane must have a sensor or sensors all over it to "receive" the laser "shot", they will be difficult to find and set up. They must not react to sunlight either, modulation of the "sending" diode will be needed and a filter of the same frequency for all the "receiving" sensors.....do not use anything that is similar to the frequency of the mains where you live.......or sub frequencies/harmonics.....it will make testing difficult in the workshop!!!! Believe me, been there and got the T Shirt.

2) I feel that 5mW will be too little power. But that is a "gut" feeling only. You will need to test over several hundred yards.....

3) Legal problems may arise due to the laser power.....

4) Somehow you need to broaden the laser beam to make the likelihood of a hit higher.....this will reduce the power effectively which is good.......for the eyes of the people watching!!

You have a hard task ahead of you....keep us informed!

Hi Andy,

You are mostly correct. Really the ambient lighting is not so much of a problem as long as you use a photodiode for the sensor. Only if you are looking directly into the sun and you reach saturation current on the device does it present an issue. A little collimation on the receiver aperture can reduce the angle of incidence to the point where you virtually have to be aiming the receiver directly into full sun for it to be a problem.

The targeting system I developed is a class II device but only out to 6 feet at which the beam power density due to beam spreading is such as to be no more of a threat than a laser pointer. And you are also correct that it is that spread that makes targeting possible and there are other means we have employed to control and degrade the "hit rate" for our purposes which I cannot describe in detail. You are also correct about the pulsing, we use a 72 kHz carrier with a 40ms pulse rate which is also important with regard to dwell time on the target since it requires a minimum of two pulese to transmit the code and achieve activation. That helps to counter the effect of beam spreading with regard to making targeting too easy.

But trust me this works and quite well. We are able to achieve target activation at several hundred yards and from a moving platform. Of course electro-optic systems has been an area I have spent many hours in developing.

Sounds very interesting, I hope to hear more in the future!!!

I wrote describing the basis for the technology you can check issue 179, June 2005 of Circuit Cellar Ink. It was for a system using IR LED's for communications signaling indoors but it scales up nicely.

Look on the web, about a year ago I found some videos doing just that!!

I just looked on YouTube and found this:-

http://www.youtube.com/watch?v=oj1vPDcuvzw

But I am sure there is a lot more on YouTube.....

Enjoy!!

Actually if you could use one of the other methods besides lasers... It would be better. Just trying to send a laser a few yards in 'broad daylight' can be difficult with 5mW of output power.

In my previous comment I mentioned 'class b' but it's actually Class IIIb

http://en.wikipedia.org/wiki/Laser_safety

And here's why there are safety regulations on lasers that use +5mW's of output power I've bolded, underlined and italicized it to point it out:

Class IIIb

Lasers in this class may cause damage if the beam enters the eye directly. This generally applies to lasers powered from 5–500 mW. Lasers in this category can cause permanent eye damage with exposures of 1/100th of a second or less depending on the strength of the laser. A diffuse reflection is generally not hazardous but specular reflections can be just as dangerous as direct exposures. Protective eyewear is recommended when direct beam viewing of Class IIIb lasers may occur. Lasers at the high power end of this class may also present a fire hazard and can lightly burn skin.

One way maybe to use a coded IR beam... Coded so that any 'outside' interference is negated... But with any of these systems - there would seem to be a problem with having to be 'exactly in a small cone' of firing to score a hit... "Side hits" - direct 'head to head' hits - and any variation would require more sensors and maybe even a microcontroller...