Wanting to test home built lidar jammer

[chris]

Cool I hope it works out for you

[Solion]

Although I had considered delays in ns for the wire length I really did not see the need to worry about capacitance/impedance due to the fact the maximum wire length from jamming head, to transistor, to home made heads is now less than 3 feet.

Although I had to bust my ass abit to find a high speed switching transistor that could handle the current and would not significantly add to the on/off delays or screw the form up.

Sadly however my Old scope has gone to the great Ohm symbol in the sky and I wont be able to do a comparison of the forms from the led heart and the heads.


but now looking at it I am wondering if it is going to be enough. given that some jammers are throwing out 50w and above with pulsed laser diodes ...

we will see how this does ( if anything ) If it fails again I will take the next step of going from 3.6w per head to 30w per head with laser diodes. then to 100w

and so it goes

[kpatz]

The key to successful laser jamming is finesse, not brute force.

Your return pulses don't have to be stronger than the gun's; in fact, they can be weaker. Consider that the gun has to read a reflected signal off your car, while your jammer heads are sending a signal direct to the gun.

So, before going crazy with lots of power, work on the timing of the pulses. Get yourself a nice high-bandwidth dual (or more) trace scope, so you can compare your head's pulses to those coming off the Blinder, and see how much delay/phase shift/loss you're getting through your wires/driver circuits.

[swarga]

Rather than having heads, how about having many strips consisting of a few LEDs mounted all over the grill, in the headlights, turn signals, around the windshield, basically every possable place on the car, so that the entire car becomes one huge IR emitter?

I think this guy stole your idea:

[Solion]

Here are the latest pictures of he new and improved jamming heads. I will be installing them tomorrow.

[fulcrum]

Designing and building a good jammer is not simple and, after the design phase, the task of transforming the prototype into a commercial unit comes with its own set of problems.

If you want to build your own jammer, then this is how I would design/build a prototype. (Just a rough list):

* Forget LEDs, and go for a pulse laser based design.
* Make the prototype modular.
- build a laser pulse unit in its own box with power supply etc. You connect this laser unit to your CPU unit using a coaxial cable with BNC connectors.
- build a laser pulse receiver unit, again in its own box with coaxial connector to the CPU unit.
- Build a CPU unit with the right interfaces to pulse transmitter, pulse receiver unit and development PC.
* If you want to cut some corners you might want to buy a complete pulse laser module, and concentrate on the receiver first.

A LIDAR jammer is a lot about timing the send and received laser pulses. You will have to measure the pulse interval of the laser gun as good as possible, and then you will have to insert your jamming pulse (again) at the right time.

Small time delays in hardware are not a problem as long as these delays are fixed.

An example of a fixed (hardware) delay is the time it takes between the pulse trigger of the CPU unit and the time the laser pulse unit actually sends out its IR pulse. (Hardware delays in the CPU unit, cable to the laser pulse unit, and the hardware of the pulse laser unit.) Because these delays do not change, they're easy to compensate for.

A more difficult type of delay is the one in the receiver. A wrong design will have different timing delays depending on the strength of the received laser gun pulse and/or the amount of interfering light. (daylight, headlights etc.) You really need a good design with the right components to minimize this problem. These receiver timing issues are very difficult to compensate for in software. Laserguns use avalange photodiode based receivers, expensive but ideal for precise timing. In a jammer 'normal' photo diodes are the logical choice.

Only when you have solved these issues it is time to create the software.

You can measure the time in the CPU unit in 3 different ways:
1: Using the stored energy in a capacitor to measure time. (Charge fast, and then discharge slow for timing resolution. This technique also works with slower CPU's)
2: Use an external (picoseconds resolution) timerchip that interfaces with the CPU. (This is how it's done in current laser guns as far as I know. Also works with slower CPU's)
3: Use the CPU internal timer to measure the pulses.

Assuming you go for option 3, then you will really need a fast (32bit) microcontroller. I think an around 100MHz 32bit RISC CPU is the minimum. ARM7 based controllers are probably the easiest choice. (There are many cheap development and prototype boards available based on this CPU family)
There are single chip controllers with enough speed, RAM, Flash, EEPROM, fast 32bit internal timers and input/output.

The ARM9 family is more powerful, but also more expensive and more complex to play around with. I don't have hands on experience with ARM9. I guess this might technically be the better choice, but maybe not for home-grown experiments. (Maybe I'm biased )

The CPU speed is important because this limits the resolution of the time measurements you can do with the processor.

Speed of light is around 1ft/ns, a 100 MHz CPU will give you a resolution of 10ft + bit errors. (This is why a 300MHz ARM9 based design can be better then a 100MHz CPU, because the timing resolution is 3x higher). Although a 32bit timer is not necessary for jamming, it will proof to be very handy if you want to sample laser gun and/or jammer output during the development phase.

Just for info. I did build my own jammer, and was able to jam my 2 different guns (Jenoptik LaserPatrol and LTI 100LR) reliable. This project crashed a few years ago on the laser receiver and lack of time. (My time) This jammer was supposed to double as a laser distance meter on a car. I couldn't get the resolution because of receiver timing errors combined with receiver sensitivity. (However the receiver was good enough for jamming purposes)

[ATF]

Laserguns use avalange photodiode based receivers, expensive but ideal for precise timing. In a jammer 'normal' photo diodes are the logical choice.

Avalanche

As for everything else, it's all over my head..

[speed-dreams]

Finally, someone has clarified this... if it were that easy as everyone thinks... we'd have our own homebuilt jammers...

[ATF]

Finally, someone has clarified this... if it were that easy as everyone thinks... we'd have our own homebuilt jammers...

I might convince some of my old co-workers to look into building their own.. Since all they do is work with lasers and optics..

[jiggly]

The key to successful laser jamming is finesse, not brute force.

Your return pulses don't have to be stronger than the gun's; in fact, they can be weaker. Consider that the gun has to read a reflected signal off your car, while your jammer heads are sending a signal direct to the gun.

So, before going crazy with lots of power, work on the timing of the pulses. Get yourself a nice high-bandwidth dual (or more) trace scope, so you can compare your head's pulses to those coming off the Blinder, and see how much delay/phase shift/loss you're getting through your wires/driver circuits.

I agree with the above.