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Thread: LED Pulse rate

  1. #1
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    Default LED Pulse rate

    Hi everyone

    In reading many of the posts here, I see reference to the pulse rate for 904nM LEDS - to jam a laser gun properly. Does anyone know what rate this is as a fact? I have seen references to 200pps (200Hz) up to 1MHz. Now, this is a REALLY broad band. Intuitively, a pulsed output is required to work, but the rate is pretty important. Eg; you don't want to pulse your LEDs at the rate equivalent to a speed of 90km/h, and then using it in a 50 zone.

    I am sure there are people here who would know this data. Care to share?

    My plans are to program a microprocessor to drive a bank of LEDs. The rate would be set by the program. It could also be made to modulate the LEDs with say an FM (or AM) pattern. Easy as ... if you have an idea about the frequency to aim for.

    Cheers, Brett

  2. #2
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    Hi Brett!

    I know 3 types only: Laser Atalanta has 238pps, ProLaserIII has 200pps and Stalker LZ-1 has 130pps. For these rates you may have laser diodes instead of LEDs as I heard but maybe I'm wrong.

  3. #3
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    Generally, the guns themselves are thought to pulse at between 100 and 300 Hz, with a pulse width of 15-30 ns, depending on model.

    Some jammers will average the first few pulses received from the gun, and then use that timing as a reference to know when to send jamming pulses, for maximum jamming effectiveness against specific models of guns, and avoiding jamming codes. In this configuration, the jammer transmits at about the same pulse rate as the gun.

    Other jammers may simply pulse at a very high rate, so that no matter what, the gun will always receive at least one jamming pulse after sending out it's own pulse, but before receiving the reflection of that pulse from the target. This is perhaps the method that is most attractive to hobbyists. The big advantage to this method is that the jamming signal does not need to correlate to incoming pulses, but a disadvantage is that this method is likely to trigger jamming codes in that targeting gun. You need a higher pulse frequency the closer you get to the gun, as the "flight time" for a pulse from the gun to the target and back gets shorter and shorter. So, you need a ~2 MHz pulse rate for consistent jamming up to 250 feet, and ~5 MHz pulse rate for consistent jamming up to 100 feet.

    Jim

  4. #4

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    I have build a few prototypes using IR-LED's. I feel the main problem here is designing a driver that is able to pulse the leds at a high enough speed. If you are not able to turn on and turn off the LED's fast enough, the receiver of the lasergun will filter it out. Driving multiple LED's at the same time makes things more complex. Although the jammer worked fine, I switched to a 905nm pulse laser and a driver circuit using a Zetex avalanche transistor. Looking back, a fast MOSFET driver could have solved the LED driving problem, but I never tried it out. (How does Blinder drive the LED's?)

  5. #5
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    Maybe you guys should tinker with diodes instead of LED's, since the diodes work better anyway. It's also easier to buy 904nm diodes. Good luck finding 904nm LED's.

  6. #6
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    Default Homebrew Laser jammers

    This is a most interesting thread,

    Like others here i am interested in constructing my own jammer, However here in the UK i have had little success in gathering data such as
    the pulse rate and pulse duration of various guns in common use.

    I would be fasinated by the info on such spec's not only of the Lidar Guns but also the common Jammer pulse rates etc etc.

    Currently i am experimenting with an analog front end with ambient light
    compensation running into a pic 16c711, the pic is only used for pulse amplitude detection and output timing , the actual jamming pulse is currently generated on a seperate pcb where i can play about with pulse rate and width etc... :roll:

    Here in the UK the act of activly using a jammer is a MORE serious offence
    (perveting the course of justice) than the speeding offence itself, thus it's not possible to ask a nice policeman if i can test his lidar against my homebrew jammer.

    Why you may ask am i doing this ?. after all i am a 50 + driver of a Diesel powered MPV, 0 to 60 in about 20 seconds not exactly boy racer stuff..

    Well i object to law enforcement hiding the cameras in bushes on straight clear roads and the other underhand methods THEY use.

    Then they (Goverment) have the audacity to make any method of self protection against there UNDERHAND use of lidar/ radar illegal..

    So please any technical info about existing laser systems which claim to
    beat the error codes etc etc please post..

    Regards Paul..

  7. #7
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    2Jim Laveg uses 600 Hz :wink:

  8. #8
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    Quote Originally Posted by BMW_525_TDS
    2Jim Laveg uses 600 Hz :wink:
    That is the highest pulse rate I've heard of on a lidar gun.

  9. #9
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    me 2 :-) but it is so... :-) how about a lowest?

  10. #10
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    Quote Originally Posted by BMW_525_TDS
    me 2 :-) but it is so... :-) how about a lowest?
    You should know. I'm going to guess the gun with teh lowest pulse rate is the stalker.

    Chris

 

 

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