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Laser Jamer Schematics/Circuit Diagrams
Hey, did a brief forum read to see if I could find any useful home-made laser jammer circuit diagrams but didn't find much, appologies if i've over looked some. Can everyone post any schematics of laser jammers they use or have made before please? Right from detection of the laser through-out to transmitting a nice confusing laser back :wink: Thanks if anyone can help me. If possible as well try to avoid ones with PIC's in cause I can't program them to save my life.
No one know any schematics then i'm guessing :P OK is there anyone here who knows exactly the specifcations of the pulses these laser guns give off then and i'll device a circuit for myself. I've done a bit more reading and these Lidar mark 3 or whatever seem to be the tricky ones to jam and something about them being impossible when used in stealth mode. What does this do to the pulses then? Anyone who knows anythinggggggg useful please leave a message, thanks.
Here's the pulse rates of many of the commercial laser guns:
LTI Ultralyte 100LR/200LR/Compact
125pps
LTI Ultralyte LR
100 pps
Kustom Prolaser III
200 pps
Laser Atlanta
238 pps
Stalker LZ-1
130 pps
Jenoptik Laveg (non-US)
600 pps
The pulse duration is generally around 20-50ns.
Jamming a laser gun is not a trivial undertaking, the guns today are very sophisticated. Evan many of the commercially available jammers havs some trouble with certain laser guns. If you expect to be able to go down to your local RadioShack to buy parts and then take them home and solder them together to make a working jammer, it isn't going to happen. So, basically that's why there aren't really any schematics around! And any that are around, probably aren't effective at all.
The trick to jamming, is to make the laser gun interpret a jamming pulse as it's own reflected pulse. The first pulse received by the gun after sending a pulse is the one the gun accepts. Anything received outside of that window is simply ignored. So to jam the laser gun, one must ensure that a jamming pulse is received by the gun after sending out it's own pulse, but before that reflected pulse is received back.
For example, the Kustom prolaser III @ 200 pps sends out a pulse every 5 milliseconds, or .005 seconds.
At 1000 feet, the pulse has a time of flight of about 2.32 microseconds, or .00000232 seconds.
So at 1000 feet, you would have to ensure that a jamming pulse reached the gun in that 2.32 microsecond window in order to have any kind of jamming effect. If one were to simply pulse laser diodes or an LED at the same rate as the gun, without being closely timed to the incoming pulses from the laser gun they would have to fall into the window at random. Using this technique, at 1000 feet you would have about a 1 in 2155 chance of having any kind of a jamming effect: .005 / .00000232 = ~2155. At 500 feet, you would have a 1 in 4310 chance. At 250, you would have a 1 in 8620 chance. And even if you were to get lucky and the pulses fell into the window at those distances, as you approach the gun there's a good chance the pulses would fall outside the window as time of flight decreases.
Historically, there have been two methods in use to jam effectively:
1) Constant-pulse jamming. This method was used by the Lidatek LE10 and Target LE850. First detect the laser, and then send back constant pulses at a very high frequency so that no matter what, at least one jamming pulse is received in this "window". If the pulse frequency is 2 MHz, this ensures that there will always be at least one pulse within the "time of flight" window, down to around 250 feet from the vehicle:
1 second / 2000000 = .0000005 seconds, or .5 microseconds.
Time of flight for the pulse @ 250 feet is .00000058 seconds, or .58 microseconds.
Therefore, at least one pulse always falls into the "window"
So to consistently jam at closer distances, an even higher frequency is necessary. This method requires overdriving the laser diode beyone it's rated specs, most are rated in the KHz range. However, they can be operated at the higher MHz frequencies for a very short time period without overheating and burning up, such as 5 seconds which is probably enough to adjust your speed. Unfortunately, jamming time is limited because of the need to overdrive the laser diode. Also, utilizing this method is not very eye-safe. This method also prevents the use of LEDs for jamming: LED's have much slower rise/fall times than laser diodes, so they cannot be operated at the high frequencies necessary and still produce pulses.
But the good thing about this constant-pulse method, is that it would probably be the easiest and most effective method that is most accessible to "hobbyists", as very little processing and timing is necessary, and it should be effective against all laser guns.
2) Time the pulses based on the pulses received from the laser gun: the "smarter" method. This method is used by most if not all of the current major production jammers. In this method, pulses from the gun are received by the jammer, and the jammer predicts when the next pulses will be received based on the previous pulses. The jammer then sends a jamming pulse slightly before the next pulse is received form the laser gun, but slightly varies the timing of the jamming pulses so that the distance calculation will vary wildly. This way, the gun always sees a jamming pulse before it's own reflected pulse and interprets the jamming pulse as it's own reflected pulse, but the corresponding distance measurements are too inconsistent to calculate a speed. The pulses can be more precisely controlled using this method, in order to jam more effectively against different guns, prevent tripping "jamming codes" on the gun etc.
As far as methods like "flooding the gun with light" so that it is unable to pick out it's own pulse from the "noise floor", these methods are not practial. Technically this could be done, but the amount of light necessary to do this effectively would probably be quite expensive to produce (a LOT of CW laser diodes used together?), and also extremely dangerous to the eyes. Lower-powered continuous light sources aren't likely to do much at all, especially using low-powered LEDs. The guns use techniques such as averaging out the noise and adjusting thresholds to prevent such methods. At best, you might be able to cut the range down very slightly, if at all.
As for simply pulsing some LEDs, you might be able to get very lucky and jam one or two of the guns (Jenoptik Laserpatrol) once in a while at farther distances (if some of the pulses happen to fall into the "time of flight" window?). But this would certainly not be consistent, and as the time of flight decreases as you approach the gun making any jamming less likely. Also, there wouldn't be any good way to improve this further, without using one of the methods outlined above.
Jim
Jim you should put that post in the "Best of" forum.
I wonder if it would be possible to use multiple pulsed diodes, kind of like a "gattling gun". It looks like you would need a lot of diodes. I suppose you could run them at reduced output, but faster pulse rate - has anyone tried this?
Also, is the pulse rate consistent from the guns? i.e. for the LTI, do the pulses come at regular 10 ms intervals, or do they mix it up? If it's regular, it should be fairly easy to predict when the next pulse would be sent.
Just kind of curious.
In my opinion that would be a VERY good method to mitigate the heat etc when using a constant-pulse technique: have multiple laser diodes that "share the load".Originally Posted by ptpark
Yes the pulse rate of the guns is fixed, and if the vehicle was stopped, each pulse would be received at a fixed interval. However, there's also the time of flight of the pulse to take into account as well: when the vehicle is moving, time of flight decreases as the vehicle approaches the gun. For example, at 1000 feet the laser gun's pulse would take 1.16 microseconds to travel from the gun to the vehicle, and at 500 feet the pulse would take .58 microseconds to travel from the gun to the vehicle. So after the cop pulls the trigger on the laser gun, as the vehicle approaches the gun it sees each pulse at a slightly "sooner" interval than the previous pulse.
If the jammer knew the distance to the laser gun (which I don't think it does) it could simply fire a jamming pulse so that it is received at the gun very soon after the pulse is sent (i.e., 1-30 ns or something). But, since the jammer does not know how far it is to the gun (that I know of), it must continue to compare pulses received from the gun in order to be able to predict the next pulse and send a jamming pulse slightly before the next one is received.
Jim
Hmmm upon yet further reading and research these jammers aren't the easiest thing to make 'at home' but my next question....hasn't anyone taken one of these popular jammers like the Blinder or anti-laser and devised the circuit layout upon inspection for themselves. They can't be as bad as a computer motherboard or anything :? i think. I'm not pretending I know more about electronics than the people who professionally make these jammers but if I was given a schematic I'd gladly try reproduce and improve them. Also by looking at the results from the "guys of lidar" tests, is there not one jammer that all the time jams every gun lol, that might be too much to ask for but it would be nice and what i'd expect if investing $300-$500 you know.
I'll be posting the schematics for a "primitive" jammer soon. Just testing a few receiver circuits. It will be a constant pulse jamming type with a few twists to it. It will be flexible enough to accommodate a wide range of LED's or laser diodes, depending on how much you want to spend. 8)
In principle it will detect a Lidar pulse, send the jamming pulses for a period of time, check for pulse, jam again, etc.
The intention is to pulse at 2MHz but with very little mods it can pulse at 4MHz in sequential mode (or even at 8MHz - depends how far you want to go).
I have looked at an intelligent jammer, but with stealth modes and variable pulse rates on the guns, I consider it a bit advanced at this stage due to lack of info on the guns.
Testing these receivers just take so much time....but I think the simplicity of the circuits will surprise a lot of people. :wink:
I suppose for regular rate lidar, you could measure the time between the first two pulses you saw, and then use that to anticipate when to send the jamming pulse, hopefully just before the next one is received from the lidar system. Since you would still be getting the pulses from the lidar system, you could judge how successful the jamming may be. I wonder if lidar systems have a mechanism for rejecting speeds when it appears as though multiple reflections are being received. I guess you could factor in the speed of your own vehicle as well, although I don't think that would help much.
I'm trying to make the design so that a microprocesser can be easily added at a later stage.
I think the next move for the Lidar guns will be to transmit at random pulse rates, hence I prefer to kick of with a constant pulse jammer. It has its own possibilities ie you could also change the jamming rate at random (say sweeping between 1 - 6 MHz). :wink:
For those that are interested, HERE is a nice book to download.
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