Wanting to test home built lidar jammer

[DrCoke]

MOAC is a man's course that CAT4 uses for testing.

[fulcrum]

I promised pictures of my "Home built" laser jammer project. I stopped this project a few year ago, because I ran out of time.... One day soon, I will pick up where I left!

Very first experiment:

This "Jammer" actually jammed my JenOptic laser gun at almost 300ft. I think this laser gun is the only one that you could jam with a setup that simple. When this gun detects IR pulses, it's software simply goes into "Help somebody tries to jam me mode", it starts screaming E14-jammed and stops getting a speed reading. This group of 16 880nm LEDs pulses at 2000Hz.

2nd Experiment

I soon found out, that I needed more power (more LEDs) and faster switch-on / switch-off times. Only later I realized that the switching times are critical, and will dictate the design of the jammer. This picture shows 2 groups of 21 LEDs switched by a MOSFET connected to a pulse generator.

1st "production" prototypes that worked OK







These prototypes were able to jam (with jammed indication E14 on the Jenoptic LaserPatrol) at ranges around 1000ft. I wasn't happy with the results so I build another prototype with more power and faster switching LEDs.


Higher power and faster switching prototype





This "jammer" had one fast switching transistor per group of 2 LEDs. A total of 32 LEDs per jammer head. This prototype actually rendered the LaserPatrol useless at any range day or night. I was so happy, until I tested with another laser gun. I found out that the switching speed of the design was way too slow. I actually connected an oscilloscope to the receiver circuit of that gun (LTI100), saw how it reacted to the pulses from the LEDs and concluded that the LEDs were not good enough. At that time I also tested with my first pulsed laser design. It was stunning to see how important the high speed switching was for successful jamming. This was my last LED based design, I will never go back to LEDs by the way....... (These LEDs are Siemens SFH487)

1st pulsed laser version



This was a prototype based on a US$ 500,-- commercially available pulsed laser driver from D.E.I. in the USA. After destroying several HP pulsed lasers with my own driver, I decided to experiment with a ready to use module, and worry about building it myself later. The output power from the laser was so much better than the LED based designs, that I never went back. This "jammer" totally blocked the LaserPatrol, but wasn't able to jam the LTI, because of pulse timing issues, it was time for a microcontroller and an laser pulse receiver.

First 2 working IR pulse receivers


Another one, build in a metal case

This receiver was part of my very first effective jammer prototype. That jammer reliably jammed the LTI and the LaserPatrol without generating warnings on the gun. This receiver wasn't good enough for what I really wanted, and that was a jammer that also worked as a distance sensor. (Very much like a lasergun). I needed a faster receiver for that....

Let's go to my LAST design, before I was forced to quit the project.

The MPU unit of the jammer

An ARM7 based microcontroller with flash, EEPROM, RAM, USB interface, fast internal timer and enough input/output lines.

The new laser pulse driver (70 Watt)




The (fast enough) receiver



I bought the laser pulser and laser receiver modules from E-O devices (USA). My plan was to build my own modules after the software was finished.

An external timer module (pico-second resolution!!)

For a jammer you don't need this resolution, but if you want to build your own laser gun or laser distance sensor then this is the way to go.

Then the project stopped...... New job, better salary, a kid and no more time.

So many LEDs

I still have a few thousand IR LEDs....... (All 880nm)

[fulcrum]

All of my posts in this thread are based on the experience I gathered building a jammer. My final prototype was ready to be converted into a production design. A multi function jammer that would double as a distance warning/measuring device with user upgradable software.
Too bad it never became a commercial jammer.

What have I learned:
- A LED based design is very much inferior to pulsed laser based jammers
- Passive jamming doesn't really work with modern guns
- The step from prototype to commercial design is big
- The laser receiver is very important for timing

What would I change:
- Probably a faster MPU (ARM9 based). The internal timer of a 300MHz processor is probably good enough for a distance sensor.

[languy99]

I like your ideas but saying led is inferior is a big mistake look at the blinder m*7, led based and it will jam everything very well. They figured out a way to do it and do it well, from your plans you were basically going down the same road LI went. Blinder must have figured out something no one else has.

[fulcrum]

I like your ideas but saying led is inferior is a big mistake look at the blinder m*7, led based and it will jam everything very well. They figured out a way to do it and do it well, from your plans you were basically going down the same road LI went. Blinder must have figured out something no one else has.

Blinder is doing two things (and there is nothing magical about it):
a) They're using 904nm LEDs, so more of the LED output is on the wavelength you need for best jamming.
b) They're driving the LEDs using the same type of circuitry that you could use to drive a pulsed laser. This way you can drive a LED to full specs. (I mean fastest speed possible as specified in the datasheet of the LED)

I know the driver design of the Blinder is superior to any of the designs I showed, but is will never be able to get the power output (in a reasonable sized box) that you can get with a laser. I could build a laser jammer based on LEDs just like the Blinder, but why bother if a better alternative is available in a smaller size and higher effective output.

A single pulsed laser has much more peak power than any LED, and it switches much faster than any LED. (Switching times less than 5ns). I believe this is the main reason the Blinder is outperformed by the main laser based jammers.

[languy99]

also food for thought, I know that the blinder heads right now are not being driven to the max, so they actually have more power available to them if needed. Did you use a look up table or were you just driving the leds/diode at a static speed (5MHz you said earlier)?

[fulcrum]

also food for thought, I know that the blinder heads right now are not being driven to the max, so they actually have more power available to them if needed. Did you use a look up table or were you just driving the leds/diode at a static speed (5MHz you said earlier)?

The LED designs presented here were only able to jam a Jenoptic LaserPatrol. It was the only gun available to me at that time, and (as I later found out) extremely easy to jam. The LED designs pulsed at a fixed freq. of just 2000-4000Hz, and that was enough for the LaserPatrol. The last laser based designs were much more intelligent, because I used a microncontroller with software. I am not sure what you define as look-up table, but the software identified and adapted to 3 different laser guns. (LaserPatrol, LTI100LR and later the Laser Atlanta)

[Solion]

Very interesting, I can see some parallels up to a point. I would love to see the spec sheets on the leds.

My first success against the PLIII came at 90khz with high current p channel Mosfet doing my switching (15ns tr/tf ,now using 12ns ones) however I did something with a little different with my large LED array, I went with building a parallel array of them (yes the current requirements were quite high) but it prevented the variable resistance changes between leds as they lit.

You went down the road of building an intelligent system which is the hardest of things to have to do, Vs the dumb HULK SMASH style that I am currently running with.

Those 2 giant arrays you have, I would love to see how they would do blown up to 2mhz (if they can switch that fast) I think you might be surprised how well it may work.

[fulcrum]

Very interesting, I can see some parallels up to a point. I would love to see the spec sheets on the leds.

My first success against the PLIII came at 90khz with high current p channel Mosfet doing my switching (15ns tr/tf ,now using 12ns ones) however I did something with a little different with my large LED array, I went with building a parallel array of them (yes the current requirements were quite high) but it prevented the variable resistance changes between leds as they lit.

You went down the road of building an intelligent system which is the hardest of things to have to do, Vs the dumb HULK SMASH style that I am currently running with.

Those 2 giant arrays you have, I would love to see how they would do blown up to 2mhz (if they can switch that fast) I think you might be surprised how well it may work.

5mm IR LED: Siemens SFH4595: http://www.nimbusworld.com/jPicts/SFH459x.pdf
3mm IR LED: Siemens SFH487-3: http://www.nimbusworld.com/jPicts/SFH487.pdf

For you information:

- Today I wouldn't choose these type of LED's. For some of the laser guns in use today, you really need 904nm wavelength IR LEDs.
- To get the switching times as specified in the datasheets, you have to design and build a driver that actually matches that speed.

(You are "advertising" the switching speeds in your design based on the specs of the MOSFET component and the LED component, but you have to realize that without the right driver circuit you will NEVER get these speeds. At the end it is the weakest link in your design that will dictate the speed reachable, even a wire of just one inch long will mess up things completely)

- The only reason my last LED design (See previous post) performs better is the fact that a single switching transistor only drives 2 LEDs through a very short circuit. And even this design was not good enough. I switched to the 3mm LEDs because of their smaller size not because of better performance. I think the SFH4595 LED is better the the SFH487, but its size was to large. Again although the SFH4595 LED is the better LED, the SFH487 performed better, just because of the design around it!!

- To drive LEDs at their rated speeds, you need a optimized circuit board (probably 2 layer). The driver has to be a avalanche type transistor, or a fast switching MOSFET + matching 1st stage MOSFET driver. The energy shoud be stored in a low inductance capacitor. (Also critical) Anything else will not be able to drive those LEDs at their max. speed.

You can measure the switching speeds of your design like this: Replace one of your LEDs by a small SMD type resistor of just 1 ohm. Connect a oscilloscope probe over this resistor, and look at the shape of the voltage across that resistor. You will need a 100MHz scope as a minimum, a faster scope would be better.

Jimbozz posted the circuit of a Blinder, this is an almost 100% copy of the typical pulsed laser driver. In fact Blinder uses 2 MOSFET's per LED. (1st and 2nd stage driver) to switch the LEDs fast. I am convinced this is the only way to drive a LED fast enough to function in an effective laser jammer.

[Solion]

Again I think you over tinked the plumbing to play the game by the lidar guns rules instead of making the lidar gun play by yours.

That's is where we differ along our thinking, That and building something simple and inexpensive. And where I see allot of confusion where it concerns what I built and what you did. And I think I should have taken pictures of the backs of my arrays to see what I have done.

My goal is and still is a cheap effective Jammer. But in Scientific terms here is my Hypothesis based on my understanding of Lidar, Lidar guns and the physical properties of light.

1) Threshold of sensitivity of a lidar gun to "see" its own pulse amongst noise generated by a high power jammer is limited.

This is supported by a well known and tested jammer called the LE-10. Firing at 2 mhz (or as high as 4 mhz) it put out an amazing level of IR, and was (still is) an effective jammer.

2)Lidar guns are not made to seriously beat jamming technology. A bold statement perhaps but really the only thing Lidar guns have really tried is to beat is sensing technology. weird rates that are not recognized or multiple pulses hidden with the pulse train. Or amplitude modulation. The guns sensing side even gated has limitations as to what it can do to try and filter for its own signal. Most guns claim a .3sec pull of the trigger to a speed reading. This does not allow a whole lot of time for in depth analysis of what it is getting back. And given the LE-10 can still jam the ever livin snot outta every gun on the planet regardless of jam code. I think proves the point.

3) Lidar gun sensor saturation. I still contend that beyond filtering for noise that the lidars sensor can be simply overloaded. Unable to detect the small changes in the noise level and reflected pulse because it is balls to the wall pegged with so much IR in the correct bandwidth that it cannot pass any more current.

My conclusion is that a few watts in the proper nm range at 2 MHZ can potentially
Jam most guns, And can be done for under 100.00 (around 50 actually.

Overall I am not trying to build a unit that can prevent a jam code. But to be honest . Jam codes have been seen in guns when no jammer is present. And if you abide not to JTG it is not going to be a factor.

Only time will tell. This weekend will be very interesting as beyond the MOAC we will hopefully do just some standard testing against the various guns