Laser Security System Circuit Design Challenge.

Designed my own laser trip wire sensor circuit and well... I felt there could be a better way to do it so why not make a design contest? Doubt very few if anyone would be intrested but in the event that your are

Principle

Design a laser sensor circuit that would everyone out including laser hobbyists.

Scenario

You are using a 1khz, 10% duty cycle low powered pulsing laser and you are shinning it at a LED sensor. The LED sensor represents the sensor on your alarm circuit.

Use so we can all see it

Requirements

Remember, this circuit needs to keep out your average laser hobbyists =P.

1. Alarm should be triggered if a pulse interrupts the system. (as does any laser trip wire)
2. Alarm should be triggered if the sensor reads nothing. (aka someone pulls the plug on your laser)
3. Alarm should trigger if sensor is pulled to a solid high (aka someone shines a laser at the sensor)
4. Alarm should be triggered if source frequency is lower then 900hz or greater than 1100hz is applied to the sensor. (aka a smart dude trys to pulse his laser at a given frequency to get past the system)

5. Output should latch (stay high) if any rule is violated and it should also have a reset switch. Its okay if it starts triggered as long as it can be reset.
6. Use as few parts as possible. Winner will be scored by how many parts he uses. ICs count as 3 parts.


This should help illustrate. If any switch is thrown besides the 1khz source the alarm should be triggered.



Try to use this template if at all possible. Template code attached. Go to file-->import--> paste code.

random person said:

Designed my own laser trip wire sensor circuit and well... I felt there could be a better way to do it so why not make a design contest? Doubt very few if anyone would be intrested but in the event that your are

Principle

Design a laser sensor circuit that would everyone out including laser hobbyists.

Scenario

You are using a 1khz, 10% duty cycle low powered pulsing laser and you are shinning it at a LED sensor. The LED sensor represents the sensor on your alarm circuit.

Requirements

Remember, this circuit needs to keep out your average laser hobbyists =P.

1. Alarm should be triggered if a pulse interrupts the system. (as does any laser trip wire)
2. Alarm should be triggered if the sensor reads nothing. (aka someone pulls the plug on your laser)
3. Alarm should trigger if sensor is pulled to a solid high (aka someone shines a laser at the sensor)
4. Alarm should be triggered if source frequency is lower then 900hz or greater than 1100hz is applied to the sensor. (aka a smart dude trys to pulse his laser at a given frequency to get past the system)

5. Output should latch (stay high) if any rule is violated and it should also have a reset switch. Its okay if it starts triggered as long as it can be reset.
6. Use as few parts as possible. Winner will be scored by how many parts he uses. ICs count as 3 parts.


This should help illustrate. If any switch is thrown besides the 1khz source the alarm should be triggered.

Try to use this template if at all possible. Template code attached. Go to file-->import--> paste code.

Click to expand...

Is this a continuation of this Thread started by AbsoluteZedo...:thinking:
http://laserpointerforums.com/f50/laser-tripwire-project-64320.html#post922058

I don't understand that sentence....

Why 1KHz and 10% and why an LED sensor....:thinking:

You ARE sending 1000 pulses every second so the alarm
would always be triggered according to your criteria..:thinking:

The sensor will already see nothing 500 times each second..

That would be a demodulating receiver set to the modulated
Laser's Frequency...
(This is easily bypassed by reading the frequency and
transmitting the same...)

Built this a few times already... I've even transmitted
RS-232 data signals over a Dollar Store red Laser beam...

There are a lot of circuits on the net to do this...:beer:
Here is one that could be "bent" to your needs and the
Laser is at the same end as the detector eliminating
the Laser power cut problem above..

Laser Target Finder Sensor


Jerry

lasersbee said:

Is this a continuation of this Thread started by AbsoluteZedo...:thinking:
http://laserpointerforums.com/f50/laser-tripwire-project-64320.html#post922058

I don't understand that sentence....

Why 1KHz and 10% and why an LED sensor....:thinking:

You ARE sending 1000 pulses every second so the alarm
would always be triggered according to your criteria..:thinking:

The sensor will already see nothing 500 times each second..

That would be a demodulating receiver set to the modulated
Laser's Frequency...
(This is easily bypassed by reading the frequency and
transmitting the same...)

Built this a few times already... I've even transmitted
RS-232 data signals over a Dollar Store red Laser beam...

There are a lot of circuits on the net to do this...:beer:
Here is one that could be "bent" to your needs and the
Laser is at the same end as the detector eliminating
the Laser power cut problem above..

Laser Target Finder Sensor


Jerry

Click to expand...

1khz is a low frequency, however, Circuit Simulator Applet wasn't built for high frequencies. Hence why a low one was used. Circuit could then be modified to use any type frequency desired.

Yup, this is a continuation of AbsoluteZedo thread, just adding a few more requirements. The missing pulse detector you showed would be fooled by an active high signal or any high frequency. For clarification, this circuit should only accept the 1khz, 10% duty cycle wave and nothing else.

Basically the challenge was to use as few components as possible in that circuit. Also building it discreetly in that circuit app which would exclude a micro. The build itself isn't anything impossible or amazing as you stated. However, the real trick again is to do it simply with a few discrete components.

Finally, i'd be rather difficult to read the frequency of a low powered laser without interrupting the system but I guess it could be done very carefully. That would indeed be a weakness. As you stated sending data would probably be the best way. Serial encrypted data would be ideal... just abit complicated to do with discrete components. Would like to see how you go about doing it.

I used in the past a different approach for plan a high security "laser fence", but then i never realized it in practic, so at the moment i don't have schematics anymore ..... anyway, the principle is the following one:

Powering the IR laser emitter at 10KHz, with variable duty cycle, where the variable duty cycle was set randomly from the "beat" generated from the main 10KHz oscillator and a second oscillator at, say, 10.005 KHz, left intentionally unstable and influenced from the environment (it was shifting a little bit in frequency with the variations of the ambient temperature, noise and light)

Transmitter and receiver was planned to be in the same box (the "fence" path had to be all around the border of a rooftop, turning the beam at the corners with mirrors hidden inside flagpoles tubes), so is easy to drive a comparator with the signal from the receiver and the signal from the transmitter (matching them for the delay, if the laser path is very long) ..... for not have any output at the comparator that trigger the alarm, they must match both in frequency, modulation and "beat shift" of the duty cycle ..... and, also, there's no way for read and reproduce it externally, "fooling" the receiver

I know, i know, i'm crazy ..... but the prototype was working, so, maybe i'm not crazy enough (must apply for do it better, i suppose )

I'm not very good at analog electronics, but I know you can use an opamp or 2 that will filter out any light that isn't pulsing at a certain frequency. not quite sure what this config is called, but it can be done for sure.

^ bandpass active filter ?

Yes, it can be done, but it still have some tolerances, with analog components.

Here there are some interesting suggestions, with calculation formulas too.