Wireless Infrared Laser Security Project

Hello !

I'd like to remotely monitor a piece of land I own.
The idea is to set an IR laser (5mW or less for safety) and IR photoresistor at knee level across the private road that leads to said land. This way if someone or something crosses the laser, the beam is cut and this activates a GSM module to send an SMS.

Could a regular photoresistor work with the IR beam ? The response @780nm looks weak according to the datasheet I found but it's there.
(GL55 series photoresistor)

As for the laser I found this on ebay:
Laser

Any idea if there is something particular to do to make it work other than hooking the right power source ?

Thanks

A phototransistor or photodiode would be a much better choice for the detector. They are more sensitive and the highest sensitivity is typically between 800 and 1000 nm.

Did not know that, thanks ! (I started inkering with arduino and electronics in general just recently)
I quickly found plenty of them on ebay.

You need a collimated LASER module, not just a LASER diode. not too common in low I.R. , but easy enough to build (you just need a low power LASER DIODE, a mount with collimating lenses, a constant current regulator/driver, and a power supply/battery).

You could modulate the LASER driver at around 38KHz with e NE555 and use a typical I.R. remote receiver connected to a digital input of an arduino. Remote receiver will output a logic high until the beam is broken. Modulating the beam and using a remote receiver will mostly eliminate interference from ambient sources.

123Splat:
You need a collimated LASER module, not just a LASER diode. not too common in low I.R. , but easy enough to build (you just need a low power LASER DIODE, a mount with collimating lenses, a constant current regulator/driver, and a power supply/battery).

Ok I looked up what a collimated laser is.
Since once it's going to be in place I won't have to move it again, it doesn't seem to be necessary as I found some laser diodes that can be focused. Or maybe I'm wrong and there's another purpose to that.

123Splat:
You could modulate the LASER driver at around 38KHz with e NE555 and use a typical I.R. remote receiver connected to a digital input of an arduino. Remote receiver will output a logic high until the beam is broken. Modulating the beam and using a remote receiver will mostly eliminate interference from ambient sources.

I had to look up what a NE55 is too :grin: Not sure I get it exactly.
Would this do the trick ?
http://www.icstation.com/ne555-duty-cycle-frequency-adjustable-module-square-wave-p-2224.html#.UvAyQrT0dC0

For a beam break setup, if you can get the simple laser and photodetector to work reliably, there is no need to worry about 38 kHz modulation. Make sure the emitter and detector are enclosed in well aligned black tubes and you should be OK.

However, as mentioned such modulation is very commonly used in IR remote controls, as it helps to avoid false signals from sunlight, etc.

You can buy IR detectors with built in 38 kHz filters and amplifiers, and there are lots of web pages, like this one, that will show you how to use a 555 timer IC to modulate a laser module or IR emitter.

Be sure not to exceed the voltage of the laser module.

And don't forget some of the non-electronic aspects of this.

How do you assure that a car, and not a dog or bird, has broken the beam?

How do you keep the tubes clear of debris, or rainwater when it rains?

You don't want lots of false alarms. For the first question above, I would place two sensors along the road, far enough apart that a dog or bird is very unlikely to break both of them.

Thanks everyone, I'm gonna try this asap