Laser activator / Laser detector Engineering

[jackenloper]

Hey guys,

It is great news that new laser activators have come out (Guys of Lidar and JTW sell them). Even though when i will shoot my detector i will only know that 904 nm wave is being emitted, not if anything is jammed by a laser jammer.

I am going to start to experiment with the laser activator (it is like a gun almost , minus the readings and the range). I think it would be possible to build a small laser detector with a small speaker that can alert to the 904nm waves.

Here is the beauty! Not all of us can afford a V1 (which is amazing as a radar detector, but it really shines as a lidar detector). If small laser detectos can be made... perhaps each of the size of an altoids box, we can put them near the license plate (just like blinder) and not have to worry about "detecting" lidar. On the jamming part, we are screwed.

Jammers are also expensive... this might be a nice alternative for some of us cheap people out there.

I just hope more people start experimenting with this idea, and we will be able to build a "good" laser detector and place the thing anywhere we want on the car. This way, we can just let the radar detectors do their job , high up on the windshield (away from the sun and overheating) just detecting radar waves.

If anybody already has ideas about the diodes or circuit diagrams to use, post them here.

[jackenloper]

I just found this site which has 890 nm and 920 nm photo diodes.

http://www.digikey.com/scripts/dksearch/dksus.dll?Criteria?Ref=369014&Site=US&Cat=32703269

What do you think about the 890 nm photodiodes?
Can they work for this project?

[JTW]

I just found this site which has 890 nm and 920 nm photo diodes.

http://www.digikey.com/scripts/dksearch/dksus.dll?Criteria?Ref=369014&Site=US&Cat=32703269

What do you think about the 890 nm photodiodes?
Can they work for this project?

These are the LED's most testers use because a small amount of the light get into the 904nm range. My tester on the other hand use four 904nm LED's specifically.

Chris

[jimbonzzz]

These are the LED's most testers use because a small amount of the light get into the 904nm range. My tester on the other hand use four 904nm LED's specifically.

Does your tester detect laser too???
He is talking about photodiodes used to detect laser, not infrared LEDs used to transmit laser.

Jim

[jimbonzzz]

What do you think about the 890 nm photodiodes?
Can they work for this project?

Yes they would work to a point, performance might be limited though. But a much more suitable component would be a SFH-203 made by Siemens, Digikey part number 475-1075-ND centered at 900nm. This component is even used in some commercial detector/jammer products.

Jim

[JTW]

These are the LED's most testers use because a small amount of the light get into the 904nm range. My tester on the other hand use four 904nm LED's specifically.

Does your tester detect laser too???
He is talking about photodiodes used to detect laser, not infrared LEDs used to transmit laser.

Jim

Oops, pardon me. Mine doesn't detect laser. The point of having a laser jammer tester is to see if all the LED's on the jammer are firing. Just because you were able to detect the laser from the jammer heads doesn't mean all the LED's are firing. What if it's just one LED that's firing? Most digital cameras can see the light from a blinder m20. All you need to do is buy a device to trigger the thing.

Chris

[fulcrum]

If you want to build a selective lasergun detector, you will need a photodiode that has a small chip size. (resulting in the fast response, necessary to detect the very short laserpulses). When mounted near the area's where the gun is aimed at, sensitivity is not a real problem, because the laserguns give a very strong (but very short) energy pulse.

Most photodiodes have a very large bandwidth (400-1100 nm) so this will normally not be a big issue. (Use one that has a IR filter to filter out most of the intefering (day)light) The SFH-203 suggested by Jimbonzzz is a very good choice. (I use the SFH-203 FA because it has an IR filter)

The real effort should go into designing the photodiode amplifier. You will have to bias the diode pretty extreme to make it work in bright daylight situations, but this is not to complex because you only want to detect ns length pulses (I use a LCR combination in the first stage of my amplifier design to do this) The amplifier should be tuned to 10MHz+ frequencies.

The last stage should be a digital filter that filters out the "to low" and "to high" pulse frequencies. (This can be done in a microcontroller or some TTL or CMOS logic)

[jackenloper]

Thanks for the responses guys.
Fulcrum, i have read your other posts about jamming laser.

I know there are two good ways of doing it, as you said:

1. sending many many beams at the gun (5mhz ocsillation), but you said that this is very tough to do with the led's and even laser diodes.

2. predict the time of the next laser shot from the gun, and shoot your own beams at the gun to try to confuse it.

My questino is, when we talk about blinder and other led based jammers. Which method do they use to jam? Do they overdrive their led's and go with the first method, or do they use their software like the second method and try to predict the next laser shot?

[fulcrum]

Blinder (LED), Lidatek LE30 (laser) and Antilaser (laser) use the 2nd method.