LIDAR Jammer

[jason]

This project is still in the early stages so I thought I'd bring it up here to see if there is any interest and to see if Ian will even allow it.

Here in the US, the police are using laser-based speed detectors (LIDAR) to measure the speed of motorists. Light emission is not presently regulated by the federal government, so there is no federal law against emitting light at the right frequency and pulse duration to confuse LIDAR. However, individual states may enact legislation making it a crime to use such a device to jam LIDAR used by law enforcement, so it's up to you to insure that its legal to use in your jurisdiction or be willing to face the consequences.

Existing laser-based speed measurement devices work by emitting pulses at a rate of between 100 to 500 pulses per second and measuring the amount of time they take to return from a target. The amount of time they take to return corresponds to the distance between the LIDAR unit and the target. By comparing a number of measurements made at different times, they can use the delta of the distance divided by the delta in time to computer the vehicles speed with some accuracy. LIDAR units emit coherent light at a wavelength of approximately 900nm which is in the near infrared region (visible by CCD cameras).

A number of approaches have been tried to jam these devices with varying levels of sophistication. Here are some I am aware of:

• Leave headlights on -- some infrared energy is emitted by most headlights -- this raises the noise floor for the pulse received by the jammer and decreases the speed detection range somewhat
• An extension of the above -- put a number of infrared-emitting LEDs on a PC board and mount it on the vehicle pointed in the expected direction of the LIDAR device
• Modulate infrared-emitting LEDs on a PC board to emit pulses designed to confuse the LIDAR speed detection device
• Modulate an infrared-emitting laser to emit pulses designed to confuse the LIDAR speed detection device

The first two approaches are of limited usefulness because while they may reduce the effective range of LIDAR, it may not be sufficient to prevent the device from working at the ranges it is normally used (the manufacturers recommend not more than 1000 feet, but they apparently work considerably further out).

The fourth approach is advocated by a number of manufacturers of somewhat expensive jammers already on the market for this purpose ($200+).

The third approach is the one I have taken myself, for the following reasons:

• Lasers are much more expensive than LEDs
• It is not clear why a laser would be more effective than an LED. Consider that while the laser in the LIDAR unit may be focused into a narrow beam in order to strike only a single vehicle 1000 feet away, a laser being used in a vehicle attempting to jam a LIDAR unit will need to be aimed in a much wider pattern in order to be sure to strike the LIDAR device.
• If the receiver in the LIDAR unit were tuned to the precise frequency of the laser, then a laser would have an advantage over LEDs in that all of its energy would be tuned to the correct frequency. However, building a filter that would operate over a sufficiently narrow range of wavelength is likely to be non-trivial and very expensive. Besides, anecdotal evidence suggests that the existing LIDAR units use CCD arrays to detect the returned pulses. This is apparent by examining the displays of the LIDAR units where you can see a rectangle placed on the target vehicle showing where the strongest returned pulses are coming from.

To compute the required pulse rate to confuse the signal processing circuitry in a LIDAR unit, the following equation can be used:

• MinPulseRate(MHz) = 1000 / (2 * d)

Where d is the minimum range you want the jammer to work in feet (light travels 1 foot in 1 ns)

I chose a minimum effective jam distance of 400 feet. This requires a pulse rate of 1.25MHz. Cheap LEDs are available with power levels up to 100mW that can be modulated at frequencies up to 12MHz and with peak emissions at or near 900nm. An equivalent laser would be very expensive. Furthermore, if the duty cycle of the pulses is kept low, the peak power levels in the LEDs can be increased considerably further multiplying their effectiveness.

Based on the above information, I've designed an inexpensive LIDAR jammer based on the following:

• I use a simple 74HC04 based crystal oscillator to generate a 12MHz clock.
• I feed the clock into another 74HC4017 decade counter to generate 1.2MHz pulses with a 10% duty cycle
• The output of the 74HC4017 drives a MOSFET which in turn drives the infrared LED

The above circuit can be modified in several ways to enhance the performance:

• Multiple LEDs can be driven in parallel by the same 74HC4017 output in order to increase the jam strength
• Multiple LEDs can be driven by different 74HC4017 outputs in order to further decrease the minimum jam distance provided the pulses emitted by the LEDs are stronger than the returned pulses from the LIDAR

At this point, I have built a prototype device on breadboard and tested it in several ways:

• Viewed the output with a camcorder to verify it is working and to compare relative output intensity with different amounts of current
• Using an oscilloscope, measured the peak current through the LEDs with different voltages and current limiting resistors in place to generate the peak output current allowed by the LED manufacturer for the 10% duty cycle and extremely short pulse duration being used.
• Used the breadboarded circuit to trigger the LIDAR detection circuitry of my commercial radar/laser detector mounted in my car to confirm that it is working.

Since I do not myself have access to a LIDAR unit, I cannot comment on the effectiveness of this home-built unit. However, there are people who specialize in doing this kind of testing and it may be possible to persuade them to test out one of these units against a commercial LIDAR if I were to provide one to them for such purposes.

This is as far as I have gone with this project at this point. The next step is to build it on perfboard and find a suitable enclosure for mounting it (which will be highly dependent on exactly where it will fit on my car). Since the front license plate is the chief reflector of light for an approaching car, it makes sense to mount the jammer as close to this as is possible, while at the same time keeping it discreet so that it is not visible to casual observers.

Some commercial jammers have detectors in them and only switch on when they detect an incoming laser beam. However, the amount of energy consumed by this unit is so small (a couple of watts), and the internal heating in the LEDs is so small that combined with their very long lifetime, I'm not convinced the extra complexity is worthwhile and am sticking with a simple on/off switch for the time being.

Let me know if there is any further interest in this. I can post the schematic and other details if Ian doesn't object. If anyone who is interested has access to more sophisticated equipment (spectrophotometer for example) that would be great, too.

[jason]

OK, I noticed that a few other people have built LIDAR jammers and written about them on the web. However, some of them don't know what they are doing(*) and those that do don't seem to be posting any schematics. So I am attaching mine here. It is unproven at this point, but it at least is based on the laws of physics and the principles of operation of the LIDAR units as detailed in various patent filings I have studied.

(*) Several people have built jammers based on sending out pulses of light in the 100-500 pulse-per-second range, which is the pulse rate of most LIDAR guns. Obviously this isn't going to work given that light will travel about 380 miles in 1/500 second. The pulse rate needs to be much higher (in the 1 MHz+ range) in order to be effective.

[jason]

Just curious, can you tell me an use/context of a LIDAR jammer not to jam LIDAR units operated by the police? IMHO the sole purpose of this device would be disabling the measurement of the speed of a vehicle/person by LIDAR.

Seems like a reasonable question to me...

1) You can use it to extend the range of your camcorder (or digital video camera) in the dark. Some of these have a switch that removes the infra-red filter and then they have an infra-red LED on them to illuminate objects that are close. The LIDAR Jammer LEDs are much more powerful than what you will typically find in a DV camera and will thus extend the range substantially. Think of it as a "remote flash" for your infrared sensitive DV camera.

2) You can use it as the basis for light communication experiments. Using pulse position modulation (simple modification of the circuit to switch between one of 10 different pulse positions) you can encode information and then broadcast it to multiple receivers that are within the beam of the transmitter LEDs. For point to point communications, replace the LEDs with a laser diode.

I'm sure there are many more things you can do if you think about it for a while. These are just two ideas that immediately popped into my mind.

Regarding the FDA's regulation of light -- I believe that applies to lasers, not to LEDs. I have some very powerful LED flashlights (200+ lumens) and there is no FDA sticker on them anywhere. I also have a 3 million candlepower spotlight (illuminates clouds from the ground) and again, no evidence of FDA regulation appears anywhere on the spotlight or in the instructions it came with. On the other hand, all of the lasers I have owned have FDA stickers on them. But they are barely regulated given how dangerous some of them are. Anyone can mail order a 2 watt green laser for a few hundred dollars which will blind anyone within a few hundred yards in the event of an accident or misuse.

[ian]

Hi Jason,

Sorry you were greeted with politics. I'm happy to have you post any circuit here until someone tells me otherwise the flow of electronics represented is so dastardly as to be forbidden to represent in the physical realm. Then I'll make sure it applies to us in the US and our sever in Germany and then comply as needed.

[ian]

Ok, this got out of hand. I'm gonna zap it. Sorry I let it go. I understand there was some disagreement over the schematic, whatever, but it should never degrade to personal insults or attacks.

[hak8or]

Hello Jason!

I have just found this project here in project development (so busy lately!) and I would like to say that the schematic itself looks nice, visually. I did not know that you can make an Altium schematic so good looking. :P

Anyways, how did you find such a high bandwidth led? I remember a few months back looking at LED data transmission using cheap off the shelf leds, but couldn't find anything that listed possible bandwidth of 1 Mhz or up. Also, I am confused as to how you are not killing the leds with so much current, even though the duration is only 83 ns. Did you get any dead leds? Also, any pictures, they are always welcome in threads! :)

And lastly, I did not see the original posts so I do not see the arguments made, but I would really like to chime in on this. While the legality of operating such a device on a vehicle is questionable in (I assume) many countries, the OP did not say he/she was going to use it on a vehicle. Maybe it was done out of curiosity, to see if such an implementation would work, which in turn could mean that it was meant to advance the OP's knowledge on the matter, and knowledge alone should never be impeded because of someones opinion on said knowledge. This project was not doing any harm to anyone, other than hurting the feelings of others through offense, so I don't see why it would have been needed to take it down. Just because information goes against your opinion or beliefs, does not mean the information should be blocked. Not to mention that if a police radar gun can be defeated so easily, then the guns were very poorly designed or planned out, showing a need to get a much more "secure" and "proper" means of measuring speed. After all, security through obscurity has never worked, is not working now, and never will work.

Thank you Ian for keeping such a project up, it is probably one of the many reasons this site is held in high regards among many hobbyists everywhere.

[jason]

Hi Hak8or,

I'm going to leave the arguments made alone for fear of derailing the thread again. Feel free to PM me if you want details.

The LEDs I've chosen are from Digikey, relatively inexpensive, and rated up to 12 MHz. I found them with Digikey's search function on their web page and an examination of the few spec sheets that qualified.

If you examine the spec sheet for the LEDs, you will see that the maximum forward current is 100mA. However, that is at a 100% duty cycle. At lower duty cycles, the maximum forward current can be exceeded. I measure over 400mA peak current through the LEDs with the circuit. With 6 LEDs, this gives a peak output power of 12 watts!

I left the circuit running overnight and then verified it was still working in the morning. No burned out LEDs. They are operating well withing the safe region defined by the spec sheet.

I have an updated circuit (6 LEDs) and PC board files available too. I will post them shortly.

[jason]

Attached is the updated schematic with 6 LEDs and a switch for running them all in parallel (for more power) or alternating them which will effectively double the flash rate and reduce the minimum effective range from around 400 feet to around 200 feet. The downside to this is that the peak output power will now be around 6 watts instead of 12 watts, which may negatively impact its jamming effectiveness in some situations.

[jason]

Attached is a zip file containing the gerber and NC drill files needed to create a PC board for the Lidar Jammer. In addition to the gerber and NC files, it contains a Bill of Materials showing the exact parts needed (by Digikey part number) for placement on the PC board. The entire board is designed to be mounted into a Hammond 1551KBK case which fits nicely behind the front grill of several cars I have tried it on. If you build it, be sure to weatherproof the case (I used silicon RTV) to protect the electronics inside. The thermal design for the system is completely lacking, although I did insure that all components used are rated for operation to at least 85C, and in most cases over 100C.

[jason]

In case you want to see what the PC board looks like (top side):



The bottom side is a (nearly full) ground plane.

[hak8or]

Thank you for providing more information and an update!

Do you have any means of testing it if it actually works? Also, it seems that the bottom right text on the PCB is not etched fully, so I assume you made the board yourself? I also notice you have a Hong Kong coin, so does that mean you are based in Hong Kong? If you are, then are there not as easy ways to get PCB's for a reasonable price in small quantities, hence you etching the PCB yourself? Also, is there a specific reason you are sticking with a linear voltage regulator instead of a switching one? I assume to keep complexity low so you can have the project done quicker? It would have kept heat dissipation much lower though, going from 12v down to 5 volts at so much current.

Hopefully tests come out positive for this project! While a few members may have responded negatively, keep in mind that DP surely has a large amount of lurkers eagerly looking at your project. Again, thank you for updating! :)


Edit: woops, I re read and noticed that you said you ordered the PCB's, not made them, so excuse that quick lapse of thought. :P

[jason]

Hi Hak8or,

As I think I mentioned in one of my first postings, the only testing I have done so far is to verify that the LEDs are working using an IR-sensitive camcorder, and I have also verified that it triggers the laser warning signal on my Valentine One.

Naturally I would like to see it tested against modern LIDAR units, but alas I don't have one myself nor can I justify the expense for this type of hobbyist project. I am hoping to rectify that by finding someone willing to test it -- there is a group of folks that do this for a hobby on the internet and I'm going to try to contact them if another opportunity does not present itself first.

The linear voltage regulator was chosen for simplicity and low cost. The power consumption is not an issue on an automobile, so the only potential downside to it is waste heat. Although the peak output power is 12 watts (pulsed at a 10% duty cycle), the average power consumption is only 1.2 watts, which translates to about 250mA of current draw. That comes out to about 2 watts of waste heat that has to be dissipated by the TO-220 package and the PC board which is used as a heat sink. According to the LM7805 specs, this is well within its thermal limitations, even with no heat sink at all.

Ultimately I will probably connect this to a second control unit which will power it with, say, 8 volts instead of 13 volts. The control unit will have something like a bluetooth module on it so that I can switch the jammer on and off from my phone, or perhaps from a module connected to my Laser/Radar detector.

The PC board is etched perfectly. The text on the bottom right reads "LJ R1.0". I believe any apparent imperfections are the result of reflections and not faulty etching.

I included the Hong Kong coin in deference to our Asian hobbyist friends out there and to take a small step away from US centrism. I'll be sure to use at least one coin from another part of the world on all my future photographs!

[jason]

Here's the completed jammer ready for mounting in my car (just in time for the holiday season when there is a lot more enforcement activity on the roads).

I measure an average current of 25 mA through each LED which is well under the 100 mA absolute maximum and corresponds to 250 mA of peak power given the 10% duty cycle on them. I could probably safely drive them even harder by using a smaller resistor but I don't want to do that until I've reduced the power dissipation of the 7805 further as it gets pretty warm to the touch with 15 volts on the input side.

Looking at the jammer with my IR-sensitive camcorder shows that the LEDs are extremely bright within their 20 degree beamwidth -- comparable to a 75-100 watt light bulb in terms of relative brightness on the display.

In the absence of anyone interested in doing formal testing with the unit, I'll be doing informal field testing myself over the months to come in combination with a Valentine One laser/radar detector and a V-8 pony car that likes to stretch its legs.

[sam512bb]

Here's the completed jammer ready for mounting in my car (just in time for the holiday season when there is a lot more enforcement activity on the roads).

I measure an average current of 25 mA through each LED which is well under the 100 mA absolute maximum and corresponds to 250 mA of peak power given the 10% duty cycle on them. I could probably safely drive them even harder by using a smaller resistor but I don't want to do that until I've reduced the power dissipation of the 7805 further as it gets pretty warm to the touch with 15 volts on the input side.

Looking at the jammer with my IR-sensitive camcorder shows that the LEDs are extremely bright within their 20 degree beamwidth -- comparable to a 75-100 watt light bulb in terms of relative brightness on the display.

In the absence of anyone interested in doing formal testing with the unit, I'll be doing informal field testing myself over the months to come in combination with a Valentine One laser/radar detector and a V-8 pony car that likes to stretch its legs.

Good day Jason,

Great work! As a suggestion, you may wish to change out your linear regulator to a switcher, as this will reduce the heat dissipation quite dramatically... With the liner regulator you are dropping 13.8v - 5 v, or 8.8V which is a hefty amount. I would suggest you look at the LM2675 switcher IC (+ inductor, diode, etc) by National (TI), or the self contained modules by TI (i.e. PT5101 series), etc.

Secondly, you may wish to place a larger cap (47uf or 100uf) on your 5V rail in order to provide some localized charge for the LEDs... 0.1 uf are pretty small and really meant to reduce switching noise, etc.

Cheers,

Sam

[southernduckie]

wow great work please keep us updated as to the results. I would assume that it would be possible to increase the number of leds just thinking of the distance a lidar can operate might need to be brighter? to be able to blind the reciever at 1000M?