Laser detection system

Alfonse

New Member
Hey all, very very new here but i really would appreciate any help you could give me on my very early staged design idea that i would like to use for my A level project. Its going to be tricky but i want to stand out and have fun with a more complex project! :)


Basically, i would like to create an identification system for the military, just a prototype, using lasers. The idea for my product is that you have a device that once you have shine a laser onto an object that has some kind of Photo transistor device on it so that once the laser has been shun onto it, i will know what type of military device it is e.g a tank, or an SUV. I was just wandering if anyone had any experience with detecting lasers from a range of about 50m? I would detect the signal with a completly seperate PIC chip which would communicate with a wireless module that will transmit a serial code back to the master PIC system that will identify what the vehicle is dependent on the unique serial code sent back.

does anyone have any recommendations of simple components that would detect a laser beam shone on it?

Any concepts or little bits and pieces that could possibly make this very brief concept into a reality would be very appreciated. Thanks! :)
 

Jeremy Harris

Senior Member
This is a common system used in the military for training, and also for threat detection*. You need to modulate the laser with pulses (for training or your proposed IFF** application you can encode this modulation) and then use a wide angle array of photodetectors (large area photodiodes with some amplification should do the job OK) to detect the laser pulses. The Picaxe can then decode the outputs and provide an IFF display.

*Weapon guidance lasers (as used in laser guided bombs and missiles, and laser rangefinders on tanks etc) use pulsed lasers. Threat detectors on vehicles and aircraft etc detect these pulses, identify the type of threat from the type of signal and provide a warning as to what it is and which approximate direction it's coming from.

**IFF Information Friend or Foe - used since WWII as a way of identifying friendly forces usually by means of a radar transponder. This worked by the transponder on the friendly aircraft/vehicle receiving an interrogation signal from a secondary radar and then re-transmitting a code to that radar. The system is still used universally to identify civil aircraft, but is now referred to as SSR (Secondary Surveillance Radar). It's the system that displays flight numbers by each radar trace on a typical PPI display you may have seen on TV.
 

MartinM57

Moderator
Welcome to the forum!

I have no idea how to do what you want (I think it would be exceedingly complicated), but strongly advise you change your "location" to just Surrey, or "Surrey, UK". You don't want visits in the night from ne'er-do-wells who might want to relieve you of your lasers :)
 

Alfonse

New Member
just trying to keep it as simple as possible so that this can be slightly acheivable. Nothing really complicated like the military have. I was thinking of using a radio module that will send data back to the PIc chip that fired the laser using serial code.

...and yeah, should probably make my address a little bit more vauge. :p
 

srnet

Senior Member
Basically, i would like to create an identification system for the military, just a prototype, using lasers. The idea for my product is that you have a device that once you have shine a laser onto an object that has some kind of Photo transistor device on it so that once the laser has been shun onto it, i will know what type of military device it is e.g a tank, or an SUV.
Giant barcode ?
 

hippy

Technical Support
Staff member
I would suggest starting with your vehicles having a large billboard that pops-up with the vehicle info when a light sensor is hit, which in sensible terms could be a PICAXE with an LCD or OLED display and a light sensor attached.

You can start with the display showing vehicle ID whenever a torch is shone on it, then you can go on to modify that so only when the torch is flashed in rapid succession.

Start simple and improve it as you change things towards what you want.
 

Jeremy Harris

Senior Member
If you're going to use light, like a laser or LED, then you have to deal with the enormous range of variation in ambient light level somehow. This is why I suggested using a pulsed light source, as this makes detection much simpler. You can easily detect a pulsed light source over a wide range of room light levels, without needing anything too complicated.
 

boriz

Senior Member
Hard to pitch and answer at the right level without more info about your capabilities. Can you design and build basic analog circuits? Do you know how to modulate LASER light? Can you program?
 

Dippy

Moderator
Absolutely start simple. And a little baclground as boriz suggests.
We can provide a lot of help and guidance but can't provide a cut'n'paste solution as it's a school project.
(I see a lot of this with students I assist at work.... :) ).

Have you seen the PICAXE BASIC Manual? The Infra__ commands?
 

Alfonse

New Member
I presume by modulating laser light you mean pulsing it by turning it HIGH and LOW repeatedley.

I do know all of the basic circuits and have an understanding of programming (finished my AS level computing).

I understand that you cant give me a cut n paste solution but all i need is just a fundamental idea of what components/sensors that can pick up laser beams from a distance. It doesnt need to be coded in any special way, just sensing the laser is enough. I think photo diodes are the way to go but i dont want to waste money until im sure of what i will need.

In my previous project i used INFRA commands so i am fairly experianced with that as well. I just need some guaidance on what components to use that could detect a laser from a distance, possibly during daylight?

Thanks again guys! :)
 

hippy

Technical Support
Staff member
would i have to use an array of photo diodes so that it has a 360 degree sensory area?
That's really your choice and it depends on what your requirements are. Do you want it to be able to detect signals all the way round ? You might need a full array, you might be able to get away with fewer, you can certainly start with just one sensor.
 

Alfonse

New Member
Thats perfect thank you so much! Also, because it has the range of the entire visible spectrum im not restricted to just one type of laser, any color should work. Cheers ! :)
 

boriz

Senior Member
There are many published examples of modulating LASER light. Do a Snoople search. One fairly simple method is using a current transformer in series with the LASER power. This has been used to transmit audio quite effectively. Does anyone know how well a standard IR RX module responds to red LASER light? Would simplify things a lot.
 

eclectic

Moderator
snip
Does anyone know how well a standard IR RX module responds to red LASER light?
Would simplify things a lot.
Indoors, at a range of ~50cm, it works fine.
(The tape-trick helps with alignment).

AXE 091 board.

18M2 tx >75 Ohm resistor > cheap pen laser.

08M2 rx connected to the TSOP IR receiver on the board.

e

Added
V+ to LASER measured at ~35mA (Too high)
75 Ohm current ~17mA
 

Attachments

boriz

Senior Member
So I guess that takes care of it. Drive the LASER direct from Picaxe (20mA max) and use the native IR commands. Simplifies things considerably.

Also has interesting implications for other applications. Like a reflective beam-break system, or 'LASER gun game', or optical comms etc. Good stuff.
 
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boriz

Senior Member
Which RX did you use? The Techsupplies one? Can you confirm if it has continuous output, or pulsed?
 

eclectic

Moderator
Which RX did you use? The Techsupplies one? Can you confirm if it has continuous output, or pulsed?
Q1. Yes, the IR RX on the AXE091 board.
And then, another on a "floating" lead.

Q2. Haven't 'scoped it.

And, a question for Alphonse.

How do you propose to keep the damned thing "sighted"?

The LASER dot has to hit a "target" roughly 5mm x 5mm.

Hand-holding is impossible, unless you're an Olympic standard shooter.

And worse, your proposed moving "tank"?

e
 

boriz

Senior Member
Simple.

The LASER is mounted on a pan+tilt servo mechanism. The RX has 'zones' that determine whether the LASER 'dot' is too far left or too far down etc. and sends, via RF link, targeting correction instructions to the LASER servos. Obviously. :rolleyes:
 

Alfonse

New Member
Firstly, just wanted to apologize and clear up what i said about the "tank" and other military vehicles. For my project i just need to prove that i can create the product but then, i would propose that it could be used on a vehicle as an identification system as a scenario for it. As a prototype model, it does not need to do these things at the start but have the ability to eventually be used in that certain situation. My bad, got a bit carried away with it and didn't properly look at what i was typing :p

Secondly, although this would not be what you wanted to do in an actual design, for my project it can be a good thing to have negative points to it such as the difficulty to maintain a clear sight. This is something that i could state in an evaluation as possible development for it. i understand that in reality, if i was making this, it would be very stupid to overlook such an obvious flaw in my design but it can potentially be an advantage and make my evaluation process much easier.

Thanks again guys, your life savers :)
 

Haku

Senior Member
How do you propose to keep the damned thing "sighted"?

The LASER dot has to hit a "target" roughly 5mm x 5mm.
Get a laser diode setup with a focusable beam so you can have a really big dot :)

Those really really cheap keychain lasers from DealExtreme are focusable.
 

Dippy

Moderator
Oh, "My Dad"... fits perfectly. Thanks boriz and that certainly made me TOL :)


I'd prototype it with an LED to get the method up and running.
 

Dippy

Moderator
Aha, thanks Joe.

The people (chaps/guys/dudes/peeps/blokes) say it at work so I knew roughly what it meant , but didn't know where it came from.

"the terrible grammar tends to drive literate people up the wall in absolute irritation."
- awesomely true. :)
 

Paix

Senior Member
Sometimes I think that there is a lot of merit in attempting to re-invent the wheel. Particularly if it keeps people from mangling the language too much. Another candidate is the occasional misuse of the word revert, when someone says that they will revert to you later. I often wonder if it has anything to do with polymorphism, alter egos etc.
 

Alfonse

New Member
Just out of curiosity, because i am fairly sure lasers is the way that i am going to approach my project. Is it unreasonable for me to use RFID's?
 

boriz

Senior Member
No. An RFID 'tag' is unpowered. Works very much like the security tags you get in shops. The tags circuit is 'excited' by the EM field around the detector gate, and re-radiates a teeny weeny bit of that power at a particular frequency. The gate listens for that frequency. Unpowered = short range, usually just a few cm.
 
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