I believe with a 555 timer you could send out low duty cycle pulses,
which would be invisible even though it is a visible laser. Short
Pulse widths in the order of a few mS on and a lot of mS off ( say 5
on, 50 off) might do the trick.... It would also serve to reject any
ambient light falling on the photodiode.... It would be fun to play
with..

On Mon, 29 Sep 2003 19:52:55 GMT, Jim Davis
wrote:

I need IR's invisiblity .
Perhaps a standard modulated TV receiver ,
fresnel lens , aluminum foil ,
and several LED's transmitting ?

wrote:

http://www.ramseyelectronics.com/cgi...ction&key=LTS1

Or you can modify a laser pointer and use a Radio Shack photodiode to
trigger the relay pretty easily... I can send a schematic if you
like...
fazelock

On Mon, 29 Sep 2003 01:24:17 GMT, Jim Davis
wrote:

I need a 30 foot outdoor IR beam "fence" ,
that closes a relay when the beam is broken .

Thanks ... Jim