Laser Beam Receptor

You don't say what if any information is coded onto that laser light beam. Is it just an on/off laser pointer you are talking about? If so what "bytes" do you expect to see as receiver circuits output? Or do you just want a high/low signal from your circuit dependent on whether it detects laser light? A component suitable to detect the laser light is a photodiode, which you will need to couple to some sort of amplifier unless you get one with integral ampifier, there are many that have such integral amplification which makes the job easier.

Steve

In fact I am looking for a laser trip circuit so that if anything comes between the pointer and receiver, the circuit alarms and then I can do the coding on my computer.

Buy a commercially available door sensor with a relay output and use that contact closure as your computer input.

Ken

For the most basic setup all you need is a photodiode with integral amplifier, this is likely supplied with +5V and will give you a voltage output on an OP pin when it detects the laser. Look in an electronics catalogue in the optoelectronics section. Some issues though. Ambient (room) lighting if high could affect the diode, how important is 100% function of this circuit? If you need it very reliable you will get into significant electronics here, and commercial kit might be the way to go! A basic method to reduce the false trigger issue might be to use a window comparator circuit to trip your output on off at certain voltage (light) levels. If you want to be pretty sure that the light you are detecting is from *your* beam then you need to modulate the sender's beam in some way that you can recognise and decode at the other end, at it's most basic using modulation at a particular frequency that you can filter out in the receiver. Reliable systems of this type are likely to use dual beams of light, spaced significantly apart - reduces false triggers due to atmospheric effects eg insects in the beam, particles whatever. I think if you want something very basic it might be OK make something yourself, but there are many commercial break beam detectors out there you'd do well to consider, including some cheap ones for domestic alarm circuits.

Steve

I did something like that. Basically set up a circuit to detect the beam break, then it signals my PC via the serial port. It is pretty easy to do. I have a circuit and sample code at:

chad

It's almost trivial, which is why I've crossposted this to the .basics group. I haven't set followups yet, because googlegroupies probably don't know how to find followups on other NGs anyway.

Go to the other side of google, and search on "photoreceptor", "photodiode", and "phototransistor" - that should keep you occupied for awhile. :-)

Have Fun! Rich