About half-way through the WUS project, I had mused about the possibility of incorporating platform lights along the edges of the track gullies. At first, I thought these would just be static lights - and probably some strand of Christmas lights that I could fenagle into evenly-spaced holes drilled out of the mezzanines.
But then some of the modern Christmas light strands caught my attention: they utilized white-LEDs instead of mini-bulbs, and they blinked. Most of them just blinked on and off, and some of them blinked in a marquis pattern. But one strand blinked in a pattern that was not merely on and off, but dim to bright.
This immediately reminded me of the blinking platform lights found in all of the Washington DC Metro subway stations, and I got it into my head that I wanted this for behind my train station.
But the special set of blinking Christmas lights didn't have the right timing, so I set about figuring out how to do it myself, from scratch.
I had read about something called the 555 timer chip before, and decided to see what Google knew about it. Within an afternoon, I had stumbled across several great web pages dedicated to tutorials on how to wire up a 555 timer chip to get on-off pulse signals.
Step one was to go buy a breadboard, a handful of 555s, and a variety of resistors and capacitors to try to get a simple green LED to blink on and off from the 555's output channel.
The hardest part of this proved to be getting the right electrical power to the 555 chip. I knew it had to be DC, so I used a small HO transformer to try it at first. This did not work at all - no signal from the 555. With a lot of help from Dale Manquen, Stan2004, and Cam on the OGR Forum, I learned that the HO transformer I was using was not outputting pure DC, but rectified AC. And this will not do anything but drive the 555 chip nuts. Fortunately, I didn't damage it: a quick test with a 9-volt battery showed that it worked perfectly, as my little green LED was blinking away at just the right rate.
Simultaneously, I was wiring up 4 white LEDs in series and testing to see if I could feed them ~12 volts DC and get them to light up sufficiently. I also started fabricating the particle-board blocks with recepticles in them, and then got the white LEDs into these. The results were promising.
The next challenge was that the signal from the 555 timer chip can only drive about 200 milliamps (mAs) of current. My string of 24 white LEDs was going to suck up quite a bit more than that.
So, I set about finding a suitable relay. I liked the idea of solid-state relays (actually, I like the idea of solid-state anything over the alternatives), mostly with the thinking that the loud clicking sounds from traditional electro-mechanical relays would be quite distracting when the platform lights were blinking.
Once again, my friend Dale Manquen came to the rescue, and pointed out a nice, affordable solid-state relay with just the right operating characteristics. It's the larger, shiny black component to the right of the two voltage regulators in the photo above.
So, the 555 timer signal drives the relay control, and the relay load switch drives the higher-current string of white LEDs. It works very well. And silently!
The very tops of the platform lights are rendered in more 0.06" styrene, which I had lasercut and etched with a nice diamond-tread pattern. The above photo shows what these look like straight from the laser shop.
And this is one of those photos that really validates the phrase "a picture paints a thousand words." From the bottom to the top, you can see here how I built each block of four LEDs. The 3/4" tall, 1" wide particle board slab is bored out with 4 holes. Next up in the photo is one of these slabs turned upside down to show that I also cut a groove into the bottoms using a table saw to allow the wires to recess. Next up in the photo shows the 1/4" slab of MDF board, to bring the height up to the same level as the rear of the train station. On top of these holes, I put small pieces of white Mylar to help diffuse the white LED light. Lastly, I glued down the now-painted laser-cut tread pattern plastic overlay, which mated up to the matteboard sidewalk level.
Another picture, and perhaps another thousand words. This is what it looks like placed up against the rear station concourse.
I finally got the other side of the track gully done months later, and now they both blink when a train is on the track behind the station, and this is accomplished using isolated outside-rail. The solid metal axles of the trains complete the blinking circuit when they enter that section of track, and so the lights stay blinking while the train is there. When the last car leaves the station, the lights stop blinking and go back to dim.
The effect is really neat, and although not accurate to reality (Washington Union Station does not have these), I like them because they add a touch of animated life to an otherwise still scene.
Especially at night, these lights help to add an eerie and distinctly urban glow to the back of Union Station.
Here's a video I took, trying to show the blinking lights as an Acela passes through on track 1. Note that in this video, the second track's lights don't blink (they're not hooked up yet). The LEDs blinking action doesn't show up all that well in this dark video, but you can see the effect on the walls of Union Station:
Blinking Platform Lights