Police lidar identification

Hello,

It's only for fun, for the technical part. I remind you that even if you detect the police laser, it is because it has already taken your speed. so please avoid me, it's forbidden, it's not good etc ...

The police use different laser guns to measure speed, which all work in the same way. Sending a laser pulse and measuring the reflection.

The goal being to detect the laser and count the number of pulses to identify the type of laser gun.

Here is what I found on the net:

  • Ultralyte Rev.1: 100pps
  • Ultralyte Rev.2: 125 pps
  • Stalker LZ-1: 130pps
  • Kustom Prolaser3: 200 pps
  • Laser Atlanta : 238pps
  • Laser Atlanta stealth mode: 238pps (2 pulses fire followed by 5 missing pulses)
  • Jenoptik Laveg: 600pps
  • Kustom Prolaser1: 380pps

.These laser guns use Laser diodes with these characteristics:

  • wavelength: 905nm
  • Average power: ~50-120uW (microWatts) (for eye safety)

For obvious security reasons and in order not to burn the eyes of offenders, the laser beam is very weak, so the receiver will have to be ultra-sensitive to detect it and only in the 850-950nm wavelength to avoid interference. especially over long distances.

I found on the net a very amplified circuit for a SHF203FA phototransistor (attached).
Is this circuit ok? and you think we can couple it to an arduino to count the laser pulse

Thank you!

azizth:
so please avoid me, it’s forbidden, it’s not good etc …

It is obviously not necessary to lecture you on that point.

But, for those reasons, I don’t think it is appropriate to provide help.

…R

Robin2:
It is obviously not necessary to lecture you on that point.

But, for those reasons, I don't think it is appropriate to provide help.

...R

We are in an "international" technical forum. Detecting a laser gun is authorized in several states in the USA and in several countries. I know that this kind of subject leads to a lot of answers of any type except technical, that's why I said that.

How do You intend to catch the laser dot with the sensor? Make the entire front into a giant sensor?

Railroader:
How do You intend to catch the laser dot with the sensor? Make the entire front into a giant sensor?

Usually the laser emission is done at a good distance, so when it arrives on the vehicle the beam of the laser is quite big. Without forgetting the different angles of the vehicle which reflects the beam and the movement of the vehicle. It already exists and is marketed.watch on youtube there are many examples of long distance detection.

Is this circuit ok?

The only way to know is to try it. You will probably need a lens and an effective near IR bandpass filter ahead of the photodiode.

A good discussion of the design issues with photodiode amplifier circuitry can be found here: http://edge.rit.edu/edge/P09051/public/photodiodeamplifers.pdf

jremington:
The only way to know is to try it. You will probably need a lens and an effective near IR bandpass filter ahead of the photodiode.

Thank you for the answer . Indeed, in order to reduce noise, but I think the SHF203FA is already equipped with this kind of filter.

I did the circuit and tried the simulated on easyeda. I sent a 500 Hz triangle waveform and amplitude of 5v (in yellow) to simultae the diode . the result seems strange to me (curve in blue), why the signal seems to decrease over time?

Since no one answered your question...
Yes, the Arduino is capable of counting 600 Hz (600 PPS) or less.

I would recommend an ESP8266 board such as the Wemos D1 Mini or NodeMCU. The Arduino Uno and Nano clock speed is 16 mHz and the Wemos D1 Mini and NodeMCU boards are 80 mHz. (Plus they have more RAM).

Here is a Frequency Counter project that may help you design a pulse counter.

My curiosity is, how will you test it?

azizth:
I did the circuit and tried the simulated on easyeda. I sent a 500 Hz triangle waveform and amplitude of 5v (in yellow) to simultae the diode . the result seems strange to me (curve in blue), why the signal seems to decrease over time?

The blue line represents the voltage on C5 which may be saturating. I don't see any way for it to discharge except through the B-E of Q4. If I am right, over time Q4 would never turn off.

Experiment with the value of C5.

Thank you for your answer, I have DUE with 84 Mhz clock, it will do the job. for the test , there is a speedgun simulator on instructable website.

SteveMann:
The blue line represents the voltage on C5 which may be saturating. I don't see any way for it to discharge except through the B-E of Q4. If I am right, over time Q4 would never turn off.

Experiment with the value of C5.

True , the C5 saturation overtime ( I try with 1khz ferquency) also I try 10uF on C5, then the blue cuvre become flat...

SteveMann:
I would recommend an ESP8266 board such as the Wemos D1 Mini or NodeMCU. The Arduino Uno and Nano clock speed is 16 MHz and the Wemos D1 Mini and NodeMCU boards are 80 MHz. (Plus they have more RAM).

You’re welcome.

The curve when i remove the C5, signal not saturing but weird... there is a way to to fix it?

500 Hz triangle waveform and amplitude of 5v(in yellow) to simultae the diode

That would be a completely unrealistic signal for a photodiode receiving weak pulses of light. Spend some time with the material linked in reply #5.

I personally would not bother with that circuit. Too many discrete parts, and it is probably intended for receiving modulated IR, as in IR remote controls.

Edit: simulation of the input stage with LTSpice strongly suggests that it is a intended for a modulated IR remote. It is a high pass filter with gain 48 dB and a 3dB rolloff of about 10 kHz.

Thank's for your answer

Speed laser gun is not far away of a ir remote , it beam a modulation of 905nm IR laser.

the optics is something that surpasses me in electronics. I think the best is to test a real circuit and see the result