As a follow-up to my previous post about Circuitron equipment, I made an interesting discovery in my collection of stuff from the 1970's-1980's. A Train Tronics Crossing Activator, Signal Flasher and two Crossing Signals that dad must have bought but never hooked up. These are the kind that used a reed switch and a magnet mounted underneath the loco to activate. So for fun I soldered the whole thing together, hooked it up and lo and behold they work perfectly. So I may as well use them (I have more than one grade crossing on my layout, so I'll buy newer stuff for other crossings) and was thinking that I can just replace the reed switches with something more modern (it's just a switch, after all), maybe something like the Circuitron or Logic Rail Tech Grade Crossing Pro use, which I think are photocells. But I don't know what type of photocells (or whatever) to get. Any suggestions on what I might use? Would I get these at Radio Shack or hobby supplier?
Photocells are provided with the Grade Crossing Pro, but I don't recommend that you use them unless you have bright light directly overhead and will never, ever, want to run simulated night operations with that light turned off. I tried the photocells on a club layout, but when the overhead fluorescent lights were turned off, even in the daytime, the crossing signals would come on and never turn off because the photocells were not receiving enough light.
I use IR side-looking emitter / detector pairs, QED113 and QEE113 (or QEE123/QSE 123) purchased from Mouser Electronics. With an IR beam aimed across the track, it makes no difference how much light there is in the layout room. The IR emitters and detectors are small enough to be mounted atop a rectangular brass or plastic tube and be disguised as posts. I mount them at the exact height of the couplers and aimed at a slight angle across the track so inter-car gaps don't cause false triggering.
There are couple of choices that I can think of.
1. a cadmium sulfide sensor berween the rails that triggers when it goes dark (car over it). They can be as small as 1/8" in diameter
2. An infrared emitter and collector. Mount at an angle so they don't see the space between cars. Put one in a pile of ties and the other in something on the other side of the track to turn it on
A better mounting method for an IR emiter and detector is to mount them in the roadbed between the ties. The IR will be reflected off the underside of the rolling stock back to the detector. Mount them so the each angle in slightly. If your detection circuit has a latching timer the gap between cars will not be an issue. Sensitivity can be adjusted by varying how much of the devices stick up about the roadbed. A much easier method to disguise. once you ballast the track they a not noticeable.