Just got a new Ramsey Electronics catlog and they sell an infrared beam alarm kit for just $9.95. Ditch the buzzer add a relay to it and you have a real cheap IR train detector. I haven’t built one yet, so I can say what modifications are needed to it. Most ICs won’t drive a relay directly so a 25¢ transistor switch probably would have to be built. Their web address is: www.ramseykits.com or phone 800-446-2295. Thought I’d pass this along.
Since you are already going to use a switching transistor and depending on what you aim to use this IR detector for, this might be a cheaper angle:
http://www.trossenrobotics.com/store/p/4861-QRB1114-IR-Photoreflector-Leads.aspx
-Dave L
That one may be good in theory, but upon checking the specs, the nominal reflective distance is only slightly over 1/8 of an inch. A better one, and a complete circuit is available through TCH Technologies. It has a reflective range of about 2 inches and will easily detect rolling stock passing overhead … and it’s only $7.95 ready to go …
Mark.
Good Link. Bookmarked
Oh and FYI when I posted that link, I wasnt really thinking outside the bounds of N scale Oops