Anyone tried DIY laser jammer?

[lostnd80s]

basically my idea at the moment is to construct a bank of IR LEDs and a high frequency drive circuit which constantly pulses them at say, 4 MHz or so. I know at high speeds and powers you can risk burning up the LED's but I figure with a large enough bank you could alternate which LED's are on and effectively lower their pulse rate. Another thing I am curious about is at what duty cycle is it best to pulse the LEDs. I am guessing something below 50%. But lower would improve upon the LEDs power handling.

Hey Charlie,

First of all, I wanted to say that while I've been lurking on this board for a while, the only reason I made an account was to discuss this project. I live in Houston, where lasers are predominant and there are no laws against jammers.

Im an electrical engineer, but my main focus is digital stuff (1's and 0's, baby! Analog is voodoo science!).

Here are a few comments I had:

- Where did you get the 4 MHz number from for jamming? I seems to me that most guns pulse in the 100-400 pps range. I'd guess that something in the 1000-2000 range would be enough for jamming purposes. In fact, I would guess that the reason most are called "shifters" is because they use the exact number of pulses per second as they detect, but just shift it by the wrong amount.

- From a digital point of view (using an FPGA as a custom DSP), I think it would be fairly straightforward to detect an incomming 100-400 pps source. You could even have multiple sensors. Last I checked, a dev board for a low power fpga like this would run ~ $50.

-I havent done a lot of work w/ LEDs. Do you need dedicated driver circuity to operate them? What amount of intensity do you expect to need?


Thanks man,
-jason

[kpatz]

For brute-force jamming, you might want to look and see how the Lidatek LE-10 works.

Detection should be easy enough in the digital domain. I wouldn't bother trying to do it in analog; that would be a daunting task. I would use a photodiode with an IR filter in front of it, and design an amplifier circuit that uses feedback in such a way to detect sudden changes in intensity (such as an op-amp with an inductor in the feedback loop). Feed the output of this amp into a comparator and your microprocessor or microcontroller and use software to detect IR pulses that repeat at a steady frequency, and when you see it, there's your lidar and you can start the jam sequence.

With a brute-force jammer, you don't really have to sweat false avoidance too much. If the sun or an Infiniti sets it off, no big deal, as long as it picks up the laser gun.

As for the LEDs, you'll want ones that emit at or near 904 nm. It doesn't have to be exact, since the lidar guns themselves use photodiodes that respond to a wider range than just 904. You'll also want ones with a fast enough rise/fall time to generate clean pulses, and enough power handling to be able to drive them to enough intensity. You can use a MOSFET circuit to provide the needed current to drive the LEDs. If you use a narrow duty cycle pulse, you can drive the LEDs with higher current pulses without overheating them. This will work fine since the gun itself sends very narrow pulses. You could make the LED circuits modular so they can be placed in the grill, headlights, and other places on the car to improve coverage. Maybe include multiple sensors as well for more reliable detection.

[untrueparadox]

why LED's? im just wondering about that since laser 905nm laser diodes cost no more than $50 for a class III 5mw one, and if that isnt enough, they have up to 500mw diodes (would blind ur eyes if u look at it undiffused). that is a LOT of POWER, more than 10-15 leds strung together. and since laser wavelength is more close together, something like 890-910 instead of 850-950 for leds, and a lot more concentrated, i think it would benefit you to look into that. also, they have pulsed laser diode drivers for sale too, so u can get a 1khz diode driver or whatever u plan to have.

ull of course need some heatsinks to go along with that, some weather sealant, a diffusing lense, but thats cheap stuff. u can basically build your own LE-10 and get as many heads as you feel is necessary. theres a forum dedicated to lasers, and i read that someone asked about building a police laser gun jammer there a while back and asked for parts and advice.

as for detecting IR, a simple camera with ir filter works fine. u can strip one off the wii controller if u can find a broken one for cheap.

but i think smart jamming algo's is what is necessary to jam today's guns undetected. this kinda setup would probably run u close to the price of a set of M27's. if successful, itll work 10x better, if not, failed experiment then. i hope u live in a state where jammers isnt outlawed yet.

[languy99]

want the best laser diode, I can get you a pulsed 250W laser diode, it costs a ton but just one with a proper driver and you can protect a 18 wheeler.