LED Pulse rate

[brett2010]

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

[T-T]

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.

[jimbonzzz]

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

[ffulcrum]

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?)

[JTW]

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.

[paul]

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..

[BMW_525_TDS]

2Jim Laveg uses 600 Hz :wink:

[JTW]

2Jim Laveg uses 600 Hz :wink:

That is the highest pulse rate I've heard of on a lidar gun.

[BMW_525_TDS]

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

[JTW]

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

[BMW_525_TDS]

nope... :-) first under Stalker is Ultralyte.. :-) but there is more under..

[JTW]

nope... :-) first under Stalker is Ultralyte.. :-) but there is more under..

The lowest pulse rate gun is the laser patrol by Jenoptik. Am I right?

[jimbonzzz]

2Jim Laveg uses 600 Hz :wink:

Thanks! I will add that to my notes :wink:

[BMW_525_TDS]

2 JTW you are still in Ultralyte class :-), forget it.... :-)

[JTW]

2 JTW you are still in Ultralyte class :-), forget it.... :-)

I'll have my Ultralyte LRB to bring to class in 5 days 8)

[JTW]

laser gun pulse rates

ProLaser III -- 200 PPS
Laser Atlanta -- 238
Stalker -- 130

Does anyone know the pulse rate of the LTI?

[JTW]

I just got word the pulses per second for LTI guns are 125 pps. I didn't get this information from LTI. Can anyone confirm this number?

[stalker]

Paul, best bet would be to get a Osprey laser rangefinder to test your jammer.

[xwarp]

I just got word the pulses per second for LTI guns are 125 pps. I didn't get this information from LTI. Can anyone confirm this number?

according to something i found on the net:

https://fortress.wa.gov/cjtc/www/classes/Lidar_Student_Manual.pdf

approximately 180 pps.

[BMW_525_TDS]

LTI 20.20 and LTI 20.20 Ultralyte are not the same.... :D

[stalker]

here is a pic of looking thru the range finder i have here...this is what u need

http://img.photobucket.com/albums/v709/radarman/Image03.jpg

[Fedds]

I two have been working on this on the side. I have concluded that using a fixed pulse rate is not a good idea. I believe this because as your vehicle approaches the cop with the Lidar gun the you could basically be feeding the gun a signal it needs. I know the right way to do it is to measure the inbound signal, calculate the pulse rate, then detemine the Phase shift required for your given vehicle speed to return a pulse train that the gun interpretes as 65MPH or what not.

The problem is that I don't think a PIC or any off the shielf micro is going to be able to sample fast enough and accurately provide the proper phase shift. After all, this technology right now is the same as in the LIDAR gun and is costly.

I still need to work through the equations again, but in college I built a laser listening device as a senior project (measured vibrations on a window of a building caused by voice and turned it back into voice..pretty sweet cause it actually worked). Since I couldn't measure phase modulation well (PM), I proved that narrow band FM (NBFM) looks a lot like PM. That said, I think by sending a relatively high pps train at a simple NBFM (or for all intensive purposes, PM) the gun will get large errors in each of the speed calculations. It might throw a jamming code, but I could care less about that.

And yes, my design was going to use a MOSFET driving system. More than likely a home brew half H bridge or totum pole configuration for fast turn off. Well have to test it a bit. The prototype will have many adjustment knobs so that if i get someone with a gun to test it, we can tune in a good jamming signal on the fly, then hard code it later.

Shouldn't be to tough considing in Ohio I don't care about the jamming code.

Oh, and I plan on using a 30-45 watt laser diode (maybe two or more depending on the price). I need to look into if this pulse duration at this power is dangerous to the human eye (although it would be funny to see the cop drop the gun and hold his eye, I'm not out to hurt anyone, just to stop getting raped on tickets and insurance).

[fulcrum]

I two have been working on this on the side. I have concluded that using a fixed pulse rate is not a good idea. I believe this because as your vehicle approaches the cop with the Lidar gun the you could basically be feeding the gun a signal it needs. I know the right way to do it is to measure the inbound signal, calculate the pulse rate, then detemine the Phase shift required for your given vehicle speed to return a pulse train that the gun interpretes as 65MPH or what not.

The problem is that I don't think a PIC or any off the shielf micro is going to be able to sample fast enough and accurately provide the proper phase shift. After all, this technology right now is the same as in the LIDAR gun and is costly.

I still need to work through the equations again, but in college I built a laser listening device as a senior project (measured vibrations on a window of a building caused by voice and turned it back into voice..pretty sweet cause it actually worked). Since I couldn't measure phase modulation well (PM), I proved that narrow band FM (NBFM) looks a lot like PM. That said, I think by sending a relatively high pps train at a simple NBFM (or for all intensive purposes, PM) the gun will get large errors in each of the speed calculations. It might throw a jamming code, but I could care less about that.

And yes, my design was going to use a MOSFET driving system. More than likely a home brew half H bridge or totum pole configuration for fast turn off. Well have to test it a bit. The prototype will have many adjustment knobs so that if i get someone with a gun to test it, we can tune in a good jamming signal on the fly, then hard code it later.

Shouldn't be to tough considing in Ohio I don't care about the jamming code.

Oh, and I plan on using a 30-45 watt laser diode (maybe two or more depending on the price). I need to look into if this pulse duration at this power is dangerous to the human eye (although it would be funny to see the cop drop the gun and hold his eye, I'm not out to hurt anyone, just to stop getting raped on tickets and insurance).

- Jamming a gun (reliable) with a fixed pulse rate, only works if you drive your laser at very high pulse rates. (Probably more than 1MHz).

- Cheap pulsed laser diodes cannot handle these pulse rates, they will overheat and burn out within a few micro seconds.

- It is practically impossible to reach a power output on these lasers that is dangerous to the human eye. A typical 40W pulsed laser could output at most a few milliwatt average power if you drive it at its maximum ratings. In a practical jammer, its output power would be even much lower.

- The range finder circuitry in a laser gun uses a trick to measere distance with a high resolutions. At the moment the gun fires a pulse a capacitor starts charging with a relatively high constant current. When the gun receives the reflecting pulse from an object (at 300 ft this would take around 0.5 micro seconds) the charging stops. To measure the distance, this capacitor is discharged with a much lower constant current, so the discharging process is much slower. (Slow enough to measure the time with a slow microcontroller at a high enough resolution)

- If you want to do range finding in "software only", you will need a processor that has an internal timer that runs at clock speeds over 1000MHz.

- You can get CMOS drivers specially suited to driving pulse laser diodes. (for example: Directed Energy Inc. (http://www.directedenergy.com)) A cheaper alternative is using an avalanche effect transistor. (for example: Zetex semiconductors (http://www.zetex.com)

- Today jamming is relatively simple, because the guns are pretty stupid. Laser Atlanta made things a little more complex, because they don't use a fixed pulse rate. I can imagine a gun using a random pulse rate, that could be very difficult to jamm.

[Fedds]

Fulcrum,
wow, really? You have you drive it in the MHz range to jam? Even if I add in some FM or PM modulation? If that's the case then obviuously I will not be able to sustain a jamming signal long at all without burning out the diode. The diode I'm looking at has a duty cycle rating of only 0.0075% with a max pulse width of 30nS. So that limits my pulses per second to 2.5kHz, and that's not very fast. We can play games with multiple diodes and alternating firing them, but from what you are telling me, we need to be smarter with out pulse phasing.

Yep, I figured there had to be an external timing circuit that was relatively slow compared to the loop time of the processor.

So you don't think around 2kHz will be enough to jam the lidar gun? Perhaps you can explain why you believe this. I just assumed that if the gun used anything like 100 to 500 pps that four times it would really make it difficult to perform it's calculation. The software in the gun has to have some error detection so that if the photodetector gets a pulse returned off the vehicle, and the same pulse also bounces back from a sign 10 yards behind the car to keep the gun from reading Mach 1 :)

I am highly interested though in your thoughts on this.

[fulcrum]

Fulcrum,
wow, really? You have you drive it in the MHz range to jam? Even if I add in some FM or PM modulation? If that's the case then obviuously I will not be able to sustain a jamming signal long at all without burning out the diode. The diode I'm looking at has a duty cycle rating of only 0.0075% with a max pulse width of 30nS. So that limits my pulses per second to 2.5kHz, and that's not very fast. We can play games with multiple diodes and alternating firing them, but from what you are telling me, we need to be smarter with out pulse phasing.

Yep, I figured there had to be an external timing circuit that was relatively slow compared to the loop time of the processor.

So you don't think around 2kHz will be enough to jam the lidar gun? Perhaps you can explain why you believe this. I just assumed that if the gun used anything like 100 to 500 pps that four times it would really make it difficult to perform it's calculation. The software in the gun has to have some error detection so that if the photodetector gets a pulse returned off the vehicle, and the same pulse also bounces back from a sign 10 yards behind the car to keep the gun from reading Mach 1 :)

I am highly interested though in your thoughts on this.

A lasergun (LIDAR) is a pulsed rangefinder, it is not an optical doppler or something. Forget about FM and PM.

I think there are 3 ways to jamm a lasergun

1) flooding with pulses at a high pulse rate.
- Assume the minimum distance you need jamming (gun to car) is 100 meters.
- It takes a laserpuls from the gun 2x100x3=600ns to travel from and to the car.
- Your jammer should send pulses so frequently, that there is always a pulse within this timeframe.
- ==> 500nsec = 2Mhz pulse frequency.
- because there is also a factor luck involved, and the gun needs more valid measurements, you can espect to have good results with lower frequencies.
- A 2Mhz pulsed IR laser can be dangerous to the eyes.
- Most (cheap) pulse lasers cannot handle these frequencies.
- This technique of jamming works with all laserguns, many will warn the user that he or she is being jammed.
- The Lidatec LE10 is the best example of a jammer using this technique

2) Sending fake pulses just before the gun expects it's own reflected pulse
- Your jammer has to measure the time beween pulses from the lasergun, in this way it can predict the next pulse.
- The jammer sends a laserpulse just before the next pulse arrives.
- By creating small random delays in this timing, the guns gets erratic distance readings and is incapable of calculating a speed.
- Today this technique works with all but one lasergun. The laser atlanta sends small bursts of laserpulses, that are less easy to predict. The software in your jammer has to be a little smarter. Not all jammers are capable of this. (I know Antilaser and Blinder jamm this gun)
- I personally expect improved lasergun software in the future, this will make jamming a lot more difficult.

3) Noise jamming
- Installing a high power source of 904nm IR light on your car.
- Modulate (AM) this signal with a broad spectrum noise signal.
- Combining with a anti-refective coating on the car might help.

Jamming at a fixed rate of 2KHz will only work on some guns. (I know you can jamm a Jenoptic laserpatrol this way) It will not work on many other guns. A gun can still get enough correct distance measurements to work out a speed reading.

[Fedds]

nope, not thinking optical doppler or anything weird. In a nut shell I was thinking more like your number two option, but I would create the random delays by modulating the frequncy slightly (FM). It would basically detect a lidar threat with a phototransistor and start pulsing at a varied frequency. I was going to bypass having a micro, but you hit the nail on the head, it's only a matter of time (short) that this will not work and the lidar gun manufactures catch on. So maybe adding a pic to determine the base frequency and then using a FM algorithm or random delay stratagy is best.

I have a another question. Is there an equation you are using to determine what is safe to the human eye and what is not? There seems to be a large set of saftey documents on the web that I am reading and many ways to figure this out.

[Fedds]

Anyone know the following:
1) How many laser diodes per head the jammer for sell use?

2) If they are just a laser diode or a hybrid (meaning the package has more than 2 leads and contains either the bulk of the drive circuit or a photo detector for optical feedback control)?

At first, I was having a hard time finding laser diodes, but now I have found so many and various variaties that I have to have a spreadsheet on price and availibility to keep it straight.

[paul]

This thread gets better, but for now just a couple of points,

In thirty years in electronics i have found that as a system is developed, and becomes more refined it takes less to BUGGER them up...

LIDAR is no different !!. It is fundementally a distance measuring system, with a few bells and whistles added.

When the LIDAR operator targets your motorcar and pulls the trigger the first couple of returns are used to calculate your initial distance.....
then a series of 50 to 100 returns are sampled to ensure there are no wild deviations or ERRORS present..if there are, another series of measurments are taken ((i belive this is why hard braking during measurement can screw some LIDAR units)) What we do is simply screw with the averages..

Ok imagine the operator just pulled the trigger.. the initial measurment puts your motor car at say 200 feet, this equates to approx 400 nS flight time for the pulse i.e. 200 nS out, it reflects off your licence plate and 200 nS back to the LIDAR unit. THEN as the software starts to sample you over say 50 pulses it expects your refelcted pulses to constantly decrease
in flight time the error trapping software knows any major deviation of data MUST be rejected and more samples taken.

What would cause an unexpeced reading ??? well the pulse train that our jammer started to send when it was first hit by I.R. from the LIDAR unit.

Pic proccessing speed was mentioned, i dont see this as a problem unless you are trying to generate the 200 Hz, 20 nS wide pulses in software
My approach was to split the device into three sections as in my original post..

My test output circuit used the Pic as the control but used a 74hc14 as both the pulse rate genny and pulse width modulator, this drove into the gate of a Mossy via a ICL7667 level converter.

What would be really great would be if one of you guys could stick a I.R. Photo diode on a scope and fire a LIDAR gun at it, and then publish the results (waveforms/data) here. And or the output from a commercial jammer as it was doing its thing...??

**Note in the UK real Laser units at 904 nM are classed as medical equipment and as such are priced at silly prices ...Thus i am playing with I.R. Leds One datasheet i read for an I.R. Led said that at 10mS "on" time it was ok to drive upto 2 Amps into a single unit....so i guess at 20nS i can do silly things ...

Regards Paul..

1nS = 1 billionth of a second, kinda puts it into perspective

:D

[bigsquid78]

[quote="jimbonzzz"]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[/

Any idea what pulse rate the zr3 is at?

[fulcrum]

This thread gets better, but for now just a couple of points,
....
Pic proccessing speed was mentioned, i dont see this as a problem unless you are trying to generate the 200 Hz, 20 nS wide pulses in softwareIn a jammer you need a high-resolution timer, capable to measure and fire laserpulses. This can be done in software, but speed of the controller in your jammer becomes a problem, unless you solve it with a fast external digital or analog hardware. A 5MHz processor clock results in a (5MHz=200nsec) resolution. A result of this problem is that jamming a gun at close range becomes difficult. (A range of 300ft is measured within 600ns)


My approach was to split the device into three sections as in my original post..

My test output circuit used the Pic as the control but used a 74hc14 as both the pulse rate genny and pulse width modulator, this drove into the gate of a Mossy via a ICL7667 level converter.
Why do you need a pwm?


What would be really great would be if one of you guys could stick a I.R. Photo diode on a scope and fire a LIDAR gun at it, and then publish the results (waveforms/data) here. And or the output from a commercial jammer as it was doing its thing...??
I will get you some pictures, just have to find the files.......


**Note in the UK real Laser units at 904 nM are classed as medical equipment and as such are priced at silly prices ...Thus i am playing with I.R. Leds One datasheet i read for an I.R. Led said that at 10mS "on" time it was ok to drive upto 2 Amps into a single unit....so i guess at 20nS i can do silly things ...
You will find it very difficult to drive a LED at those speeds, and still getting the power output you want.


Regards Paul..

1nS = 1 billionth of a second, kinda puts it into perspective

:D

[Fedds]

I would like the files as well, if you don't mind

[jimbonzzz]

Yeah, me too.
I looked at the pulses from the Stalker LZ-1 on a scope briefly this past weekend. I was a bit surprised that I could see such short pulses on a 20 MHz scope. They seemed to rise slowly and fall quickly, maybe this was the photodiode that I used though...

Jim

[paul]

Hi Fulcrum.
Thanks for the feedback, and offer of some extra info,

I would like to clarify a couple of points thought..

(1) Clock speed and resolution,

I entirely agree with what you said regarding the limited resolution even with a 5 mhz clk, however I am only using the Pic for control and NOT any timing critical detection or generation of pulses.

Detection of incomming LIDAR pulses was done in the onboard ADC by looking for the signal to exceed (In amplitude) an arbitary present level, The jamming pulses are generated on an other pcb.. Thus the Pic really only acts as an amplitude detector, and control timer switching on my external clk cct for 3-4 seconds and sounding a small piezo alarm.

(2) Opps.. a typo error this.

I use a 74hc14 as my main pulse genny this allows me to play about and adjust the CLK from just a few hundered hertz to several khz this feeds into the next stage which i described in error as a PWM in reality its more akin to a trigger cct where i can trigger on the incomming leading edge and adjust quite accuratly the "on" time of the outgoing pulse.
example: square wave input at 200 hz 50:50 mark space, to an output at 200 hz & 100 nS "on" time. (the "on" time is adjustable)

(3) Be great to get some info from you Thankyou..

(4) Hmm this was a comment that was a bit tongue in cheek but was based upon the following.

I felt there were two possible ways open to me to jam LIDAR,

(A) Brute force where we simply generate as much I.R. as possible to block the Lidar from seeing its OWN reflected pulses.

(B) Stealth where we generate a somewhat lower level pulse but endevor to fool the gun into thinking it actually its own reflected pulse, we ensure our Pulse rep rate is fast enought that our pulse is always the first to be recieved by the LIDAR, getting an almost instantanious reflection should cause the error trapping to kick in thus achiving a jamming situation..

At the moment i am experimenting with (B).

What would be facinating to see, would be the pulse waveforms from both a I.R. led based jammer, and a genuine 904 nM laser diode. I suspect that the genuine Laser diode will be driven at high speed possibly with <30 nS pulses, where as the I.R. led would most likely be driven with a somewhat longer duration pulse (relativly speaking). This difference could possibly account for why some jammers generate error codes and some dont.

Ok at this point a lot of this is guestimation as i have NO access to any LIDAR guns or existing jammers, so i would be really please to get more info from you guys....

Best regards Paul..

P.S. In the U.K. we have approx 4500 fixed speed traps and 2500 mobile LIDAR units, plus systems such as "specs" and other obcenitys all based on cameras...... And then think the U.K. is smaller than a lot of your seperate States.... :?:

[Fedds]

the 74hc14? Isn't that just a 6x schmitt inverting trigger? Do you plan on running a 555 timer or something infront of this or what to generator your pulses? Go a web page or schematic of what you are trying to do?

I would like to be able to control the freq and duty cycle with the pic. I might try to due this and build a small circuit that divids the duty cycle to get the short pulses I need. This way is just a code download to change. I don't like pots unless they are digital :)

what laser diodes are you guys looking at, two or three wire (one with a photo detector built in to regulate the optical power or just the diode)? I'm looking at the ones from PerkinElmer, specifically the PGEW low cost diodes The Duty factor is low, but the laser diode in 30watt peak power is $33. I'm also looking at series from OSRAM, part SPL PL90_3 and it's $39.25 with 25 watt capability and the great thing out it is that it has an intgrated driver stage. So again I ask, what diode are you guys looking at and how much are they (power and cost)

[fulcrum]

You cannot regulate the duty cycle of a pulse laser diode, nor do you need to for a jammer application. In many designs you discharde a capacitor over the laser using a special cmos switch chip or avalanche effect transistor. The power and duration of your laserpulse depends on the capacitor, the voltage you charge it with, the type of laserdiode, and many very subtle factors in the design and components of your laser pulse circuitry and board layout. These are high frequency high power designs that will create many problems for the unexperienced. (Including to a certain level myself)

How to build a (prototype) laserjammer:

- Buy or build a good laser pulse module. options from easy to difficult:

1) Buy a complete OEM board from Directed Energy Inc. (This is a great solution for your first prototype)
2) Design and build someting around the 3 wired OSRAM laser. (This pulse laser has a capacitor and fast cmos chip integrated)
3) Design and build someting around the more common 2 wire laser chips using fast cmos switches (DEI is one of the companies that sells these components)
4) Design and build something around the Zetex avalanche transistor and a 2 wire pulse laser diode. (cheap, but very difficult to get things working reliable without blowing up many of laserdiodes.....)

- Design and build a laserpulse receiver module that is fast, stable and interfaces to your cpu/logic.

- When you have these 2 modules up and running, connect them to a development board with the processor of your choice.

- Write the software..

[Fedds]

sorry Fulcrum, buy duty cycle I think I meant duty factor...it's been a long day.

I have found many "typical" laser diode drivers that operate as you described using the cap discharge method.

You plug DEI quite a bit, do you work for them :D Anyways, $190 for a PCO-7110 series driver seems a bit high for a hobby project. Granted, if I'm not careful and really ring out the drive circuit I might spend more than that in diodes alone.

Even the OSRAM 3 wire seems kinda pricey at $53.39, but then again a 2 wire one is around $40, so maybe it's not so bad.

I guess it just depends on your goals. For me, this project to to create a jammer that is lower cost than the production ones and let anyone what's the schematic and source code have it. That said I have a good start on something along the lines of option 3 and 4 as you have stated. I think as long as I can build a dummy load that represents the diode for test I should be in good shape and not go through half a dozen expensive laser diodes.

[fulcrum]

sorry Fulcrum, buy duty cycle I think I meant duty factor...it's been a long day.

I have found many "typical" laser diode drivers that operate as you described using the cap discharge method.

You plug DEI quite a bit, do you work for them :D Anyways, $190 for a PCO-7110 series driver seems a bit high for a hobby project. Granted, if I'm not careful and really ring out the drive circuit I might spend more than that in diodes alone.

Even the OSRAM 3 wire seems kinda pricey at $53.39, but then again a 2 wire one is around $40, so maybe it's not so bad.

I guess it just depends on your goals. For me, this project to to create a jammer that is lower cost than the production ones and let anyone what's the schematic and source code have it. That said I have a good start on something along the lines of option 3 and 4 as you have stated. I think as long as I can build a dummy load that represents the diode for test I should be in good shape and not go through half a dozen expensive laser diodes.

I would never use the DEI modules in a production version, they're much to expensive. But if you want to get started quickly, it's an easy way to go. (I did it after destroying to many osrams)
I am using the 3 wire osrams in my own design now. (low voltage driver is nice!!)
And no, I have no links with DEI at all!

[paul]

Hi Fedds,
Your correct its a six element device, one is used as a pulse generator, one is used to control the pulse width, and the remaining four can simply be hooked together to act a a buffer stage..I will scan my hand drawn notes at work tomorrow and send you a pm over the weekend...

(is there a files section on this forum ??)

RE: your use of the pic to generate jamming pulses in sware..
Fulcrum had a very valid point about timing resolution !!! trying to generate a pulse of approx 20nS when each CPU clock cycle has a longer periodic time could be somewhat difficult...

What catches my interest here is that 'we' are drifting towards looking at high tek solutions, where as the commercial jammers actually work, using low tek I.R. Leds (low cost Maximum profit)

Hence it makes me wonder just how Hi tek the electronics really are ?
in the commercial product.

Come on someone,, rip the lid of your blinder or such and tell us whats inside..

Regards Paul. :?

[fulcrum]

Once more: you do NOT have to control your pulsewidth. It is set to a fixed time by the laserdiode pulsedriver circuit, and it's value is really not that critical for a jammer. (As far as I was able to test, any value between 5ns and 50ns is ok) There is also no need at all to change the pulsewidth at any time while your jammer is running. Just match the driver to the laser, and go for 10-30ns that's all!

Except for some analog filtering in the receiver circuit, a laser gun is doing nothing with the width of a received pulse. This filtering is only important for a gun to be able to amplify the signal from its receiver photo diode, and separate it from the background noise. Basically the gun responds to the leading edge of a received laserpulse only! The lasergun receiver is just tuned in to the length of it's own pulsewidth. (Very much like a radioreceiver is tuned in to the frequency of a radiotransmittor. This is the only way to make a IR photodiode amplifier stable at the very high amplifications necessary for a lasergun to work at bad (Veilled 8)) targets)

When I'm talking about timing resolution by a cpu, it has everthing to do with WHEN to trigger the pulse, the cpu does not control the pulse length. It also is important to exactly know WHEN the jammer receives the pulse from the lasergun. The time between receiving a pulse and sending one could be so short, that it is shorter then 1 clock of your (to slow) cpu. This timing issue limits the MINIMUM distance your jammer is effective (and/or doesn't trigger a JAMMED code on the lasergun)

Just imagine that your jammer is a laser range finder. If you would do this completely in software on a 10MHz cpu, you would have a 100ns +/- 1 cpu clock = 300ns resolution. In this case your rangefinder would have a 150ft resolution. A 100Mhz clock results in 15ft etc. (I'm taking some shortcuts here, but basically this is the problem)

Discussion lotec/hitec; At the end a jammer based on a pulse laser diode might cost 10$-35$ more. (Looking at component prices). I personally would never design a LED based jammer, because of other problems that you will encounter using LEDs.

[outrun]

Ok the stalker and Ultralyte are pretty much the hardest to jam so does that mean the slower the pulse rate the harder it is to jam?

OUTRUN

[fulcrum]

Ok the stalker and Ultralyte are pretty much the hardest to jam so does that mean the slower the pulse rate the harder it is to jam?

OUTRUN
no

[fulcrum]

This is the picture I promissed, but it's not a JenOptic Laserpatrol generating the signal. I used a laserpulse from one of my labs test units.

It is a laserpuls at a pulse repeat freq. of 100Hz (the green line) and the signal of a Lidatec responding to it. (the red line). The red pulse doesn't really look like a short pulse, because of the slow photosensor i used in this experiment. What you can see here, is the lidatec sending the pulse before it expects to receive the next pulse from the lasergun.

http://www.rebuildgroup.nl/images/LRC100_p1.jpg

[Fedds]

interesting picture. Looks like the tough part is trying to determine the frequency of the incoming pulse train from the lidar gun and then providing proper phasing.

I think I'm going to go with the OSRAM 3 wire as well, since it seems a bit easier for me (and a little harder to fry the diode). I too enjoy the simplicty of designing low voltage drivers (where I work, I have had to design drivers for high inductive devices to be driven at high frequencies that still passed EMC...it can be challenging to do cheaply).

[Vonkie]

So Fedds, how far did you get??

Why did this thread go so quiet?? :(

[RapidTransitSystem]

could i make a custom laser jammer using PIAA leds? they come in sections of 6 leds for fog/driving lights. Could they possibly be used for jamming.

[Vonkie]

I don't think so, the radiation spectrum for those is way off from the 904nm wavelength rquired.

[Run]

Long time ago since anybody wrote in this thread. When I started to read from the beginning today, I imagine an useful pruduct at the end. So then a complete drawing, componet-list etc.
Come on boys :o :wink:

Res Non Verba :wink:
Run

[411]

Long time ago since anybody wrote in this thread.

Run , true not much is coming out .

But the interest is still very strong.

I found a product that states :

• Pulse widths from 5 to 30 nanoseconds .
• PRF up to 40 kHz with integrated power supply.
• Discharge current up to 75 Amps peak power.

If we could find somebody that could modify/test this unit .

The link for the pdf :http://www.eodevices.com/pdf/ds_etx12.pdf

I don't have enough knowledge just to buy one for fun but surely it could be a good base. The price is around 200 uscy , this include the laser diode osram SPL PL90.

I quote Jim here :


Time of flight of the gun's pulse with the target at 1000 feet is about 2 microseconds: so you have a 2 microsecond window for a jamming pulse to be received. If your jamming is pulsing at 10 KHz, that is only one pulse every 100 microseconds. 100 microseconds / 2 microseconds = you would have about a 1 in 50 chance of a jamming pulse falling within the "window". And it gets worse the closer you get to the gun: if the target is at 500 feet, time of flight is only .5 microseconds. So you would have about a 1 in 200 chance of a jamming pulse falling into the "window".
http://www.radardetector.net/viewtopic.php?t=11059&highlight=

So firing at 40,000 shots per second @ 30 ns , the chances of confusing the laser should be quite good .The unit in question is modifiable to fire up to 100 khz.

Knowing is everything. Hope this thread keep cooking .

[411]

http://www.eodevices.com/Images/eil-2%20module.jpg

The ultimate jammer , in my dreams ,


EIL-2 accommodates up to 12 Laser Diodes / Emitters (OSRAM or any TO-18 style).
Each Laser Diode has choice of vertical or horizontal mounting orientation.
Each Laser Diode has approximately +/- 20 degrees of tilt adjustability.

[radardan24]

i think you take a bought blinder and a bought zr3 and use all 3 up front against same gun. i think the zr3 or lp905 wll beat blinder using almost any gun except stalker. everything else, the lp905 own it.

[Suf Daddy]

Guys of LIDAR.com and my post (last week) on RD.net (here) referencing the book Roy sells: "Understanding Police and Traffic radar and Lidar" has a table.

LTI's have 125 and possibly 100 pps.
maybe not the lowest, but my expertise only goes to US LIDAR guns............

-Suf Daddy



I just got word the pulses per second for LTI guns are 125 pps. I didn't get this information from LTI. Can anyone confirm this number?

[Suf Daddy]

I have no idea, these guys are over my head...........

BUT:

I read you could take spot lights (like on rally cars) and cover them with IR filters (one that allows 904 nm through.............)

and flood /overload the LIDAR gun. you'll get jamming codes (E-07) on LTI's - for example-, with this approach.............

-Suf D8ddy



could i make a custom laser jammer using PIAA leds? they come in sections of 6 leds for fog/driving lights. Could they possibly be used for jamming.

[BogeyOnYourSix]

I'm a recent EE graduate and looking into creating a lidar jammer of my own. (Interestingly i'm working for a company right now that uses IR detection systems in their products. Note their not lidar guns, but you can see why i'd be interested in doing this.)

If anyone has access to a lidar guns and an oscilloscope, please post the pulse waveforms for the benefit of the community. :idea:

I was able to find a patent for a lidar jammer which was very informative:

http://www.google.com/patents?id=m50lAAAAEBAJ&printsec=abstract&zoom=4&dq=Laser+transponder+for+disabling+a+laser-based+speed+monitor#PRA2-PA2,M1

[Eloi]

An idea to make a simili blinking led :

Use a constant led and place the led behind a fan with variable speed ...

would the passing blades create a workable blinking led ?

I dont want to build a jammer on this threory , just want the opinion on the principle . Thanks.

[BogeyOnYourSix]

that would work... make an aluminum disc with small slits/holes in it and spin it really fast. You'd have to do the math on the rpm's, slit width / hole diameter, and number of slits to see what kind of frequency you'd be able to get.
I might experiment with that myself.

If you're going for a low frequency application, it be much simpler just to make the led blink with a 555 timer.

[charles charlie charles]

You would have to have the disc spinning continuously, not just when a LIDAR gun was detected (due to the obvious spinning up time) which would fairly quickly reduce the longevity of that kind of system.

[Eloi]

Found this article , anyone has an opinion/test made on this jammer , seems to come from Korea ...led based ....personnally I would not buy because of no upgrade would be available ....and led is an ''old'' technology ...versus laser diode.

http://www.speed-dynamics.de/assets/images/autogen/a_camouflage3.jpg



Not sure if I could put the link page ?

[LittleOverPSL]

That's a very interesting idea Eloi. Spin up time is a good point, but that could be countered with a brushless motor that is constantly spinning (say at some median speed between target minimum and target maximum). The jammer could then adjust the spin speed once it figures out the lidar gun pulse rate and the desired pulses to be 'fired'.

The neat thing about this approach is that the LED array could be always on and counter their slower rise/fall times. However, timing the jam pulses accurately will probably be a real challenge.

Maybe a better approach is to use a very high speed shutter.

Of course, moving parts are prone to failure. So that limitation/challenge still stands.

[Eloi]

That's a very interesting idea Eloi

Thanks Psl ... :)

More on the idea : using a fan from computer , I was able
to light a led connected to the input wires and holding
the fan out of the window , the fan starts to turn @ +- 20 mph : led on
( brushless 12 volts .13amp fan ) ,
a mini-generator . I tried with another computer fan ....
and it did't work ? :cry: can't figure why .

The output could be used via a very small relay and
be used as an automatic on/off switch for the jammer ...

[fulcrum]

Do you really believe spinning a disc with one or more holes in front of a LED at the right frequency and the right synchronisation and the right pulse shape is a practical solution ???

And to end this discussion:

- Take a disc with a diameter of 100mm
- Drill a hole of 5 mm (LED size)
- spin it at 6000rpm (for a 100Hz pulse)
- The hole travels at around 31400 mm/sec
- It will take the hole 0.16ms to pass the LED
- This will give you pulses of around 160000 nsec

- You need pulses of I guess less than 100ns


- The lasergun will filter away this signal
- You waste most of the radiant power that the LED will give you

- Even the most simple electronic solution for switching on and of a LED is far superior.
- However you will need a very advanced electronic solution to pulse LED at the speeds/power required.


FORGET IT!

[LittleOverPSL]

1. Does it really have to be a round hole? Could it not be a 5mm long slot (just like they did in SLR cameras) say about 1mm wide?
2. Does there have to be only ONE slot/hole on the disc?
3. Does it have to be a disc whose face is in front of the LED? Couldn't it be a band that goes around the LED?

Mankind hasn't reached where it's at by thinking inside the box. I am not saying it's the most practical solution. Maybe it's a dead end, is there harm in someone experimenting/exploring?

[Eloi]

And above all , it is fun spinning a disk :D

http://www.exploratorium.edu/snacks/gen_images/whirling_watch_1_397x275.gif
We dont want to build a jammer , we are exploring concepts......

The name of this disk is stroboscope :roll:

[BogeyOnYourSix]

Do you really believe spinning a disc with one or more holes in front of a LED at the right frequency and the right synchronisation and the right pulse shape is a practical solution ???

And to end this discussion:

- Take a disc with a diameter of 100mm
- Drill a hole of 5 mm (LED size)
- spin it at 6000rpm (for a 100Hz pulse)
- The hole travels at around 31400 mm/sec
- It will take the hole 0.16ms to pass the LED
- This will give you pulses of around 160000 nsec

- You need pulses of I guess less than 100ns


- The lasergun will filter away this signal
- You waste most of the radiant power that the LED will give you

- Even the most simple electronic solution for switching on and of a LED is far superior.
- However you will need a very advanced electronic solution to pulse LED at the speeds/power required. Interesting idea nevertheless.


FORGET IT!

I did the math on it too, i think it was like 20k rpm with 1000 holes to make it viable... Which isn't impossible, but i wouldn't use it for this application. Interesting idea nevertheless.