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Jerry,

You're going to have some difficulty making them work exactly like they did when in service for the railroad. The basics are, the signals usually work on a DC circuit that's backed up by a couple of large batteries in the silver box you see by the side of the track near the crossing. There are three track circuits that make the signals work, and these are "shunted" or closed when the metal wheels of a train allow current to pass from one rail, through the wheels/axle to the other.

(For the C&S types among us, this explanation is DELIBERATELY simplified!)

The three track circuits are the "approach" circuits, which extend from where the signal first activates from either direction to the edge of the "island" circuit which covers the actual crossing of the road plus a little on either side. Simply, when a train enters either approach circuit, the signals are activated, and the opposite approach circuit is disabled. When the train enters, and then LEAVES the island circuit, the signals stop. When the train leaves the opposite approach circuit (which is disabled, remember, as we don't want the lights flashing while the train passes through it, after leaving the road) the system resets. If there are signals on the line, or more than one crossing, or switches in either of the circuits, or more than one track, it becomes even more complicated, and remember my explanation here is just the basic approach. If you add gates, there are timers and motor drivers to make them work. That's why that whole case is filled with relays and controllers.... and it's also got to work when the mains power is off. And, as you can see, activating the signals and then stopping and backing out of the circuit, or stopping in the approach circuit on the far side and backing up can have bizarre effects on what the signals do, if this kind of movement is not planned for.... and you can either have signals flashing when a train isn't approaching, or signals that don't come on for an approaching train. Rusty rail, debris, broken bond wires between rails ... all that stuff TOC likes to preach about for track power applies to the 1:1 railroad here, and causes the same kind of frustration.

More modern signalling involves predictor circuits which monitor how fast a train is approaching and whether it's stopped, and modifies the "lead time" of the signals accordingly, so that if the train stops before reaching the crossing, the lights stop, and if a train enters a circuit timed ro a 70 mph train going 10 mph, the signals will wait until he's closer to the crossing so that the lead time is the same 27 seconds (well, that's the minimum, anyway) regardless of speed.

But, the bottom line is, prototypical, you'd need to shunt a track circuit, and your UPS fellow isn't going to do that. For your yard system, what you probably need is a timer, a 24 volt relay, and a "wig wag" flasher capable of handling 24 volts. Using the kind of trigger a gas station bell uses (you know, the hose with the pressure switch...) the trigger would activate the timer, which would turn on the 24 volt relay, sending power to the bell and the wig wag flasher.... operating both for 30 seconds or whatever time made sense to you, and then stopping. It'd activate again as he left the driveway, but that might not be a bad thing. You could power the whole affair with a couple of car batteries and if you wanted to be really slick, you could use a charger and solar panel to keep the whole thing charged and ready.

Matthew (OV)
 

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The problem with using a 537 relay (the turn signal flasher) is that you get an uneven flash pattern ..... FLAAAAASH ... flash... FLAAAAASH....flash .... if you're only flashing one light, it's OK, but quickly you'll see one stays on a lot longer than the other. (in a car, where one is your flasher, and the other is the light on the dash, nobody cares.)

You can use a police "Wig Wag" flasher, solid state, even rate... but it's generally WAY too fast (3 per second, often!) for what you want. Better to build one, or use something else with an even, slow flash rate. Commercially, there's options like this: http://www.trafficlights.com/b2ad.htm but that's just a quick google... there may be better ones out there.

Matthew (OV)
 

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Jerry,

Wouldn't worry about the extra couple volts. The current draw should pull it down anyway... but it's just a light bulb. Most automotive 12 volt bulbs are being fed 13.something by the alternator anyway. You could always use automotive bulbs instead.

Does your sign have four bulbs or two? If it's only two, remember you're only turning on one at a time.....

Matthew (OV)

Oh, and semper... nice idea.. Do not STEP on tracks!
 
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