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.
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
