We toured the Central Library’s new Bausch & Lomb building on its opening day, back in 1997. Being the proud parents of a toddler, we naturally visited the new Children’s Center on the second floor. I noticed the glassed-in space under the stairs immediately. “Good place to put a railroad,” I thought. It took me seventeen years to turn that idle notion into reality, but here it is.

The challenge wasn’t getting a railroad into the space, but making it operable. And by “operable,” I don’t mean in a plug-it-in-and-let-it-run-all-day kind of way. I’d rather not run the wheels off my equipment if nobody’s watching. Besides, I wanted interactivity. Kids at train shows have to be spectators. I wanted to offer them an opportunity to actually control the train. But how?

Knobs or pushbuttons were quickly eliminated from consideration; they’d need wiring to pierce the wall, and that wasn’t going to happen. Some kind of light sensor on the glass seemed the ticket, so I did some research (this was in my pre-internet days), got components from Radio Shack, and prototyped a circuit with a phototransistor and a 339 op-amp chip. It sorta worked, until I put glass over it. Feeling stuck, I set it aside for a decade or so.

My recent successes with Arduino-based electronics got me thinking about the light-sensor throttle idea again, so earlier this year, I took a fresh stab at it. This time, I got a circuit that worked to my satisfaction, even through glass. I pitched the idea to the library, they liked it, and we set an exhibit schedule.

The layout itself is pretty simple—just a few of my T-Trak modules, fresh from the RIT show, arranged on a six-foot table. Instead of running trains at RIT on Sunday afternoon, I set up my soldering station in the operating pit and assembled the throttle circuit. Two small perfboards each contain an infared LED, a phototransistor, and a regular green LED. Each of these sensor boards is taped to the back of a cardboard faceplate with my incredibly crude “place hand here” graphic. Infrared light reflected from your hand is sensed by the phototransistor, which feeds an analog input on an Arduino, which in turn controls the track current with a transistor.

I installed everything late Monday afternoon, and to my relief, the circuit worked as intended. A visit back to the library on Thursday evening revealed a problem: running both trains simultaneously causes the circuit to shut down and reset. Maybe the wall wart I’m using isn’t robust enough. Maybe my old Life-Like SD-9 is drawing more current than I thought. Maybe the code in the Arduino is doing something funny. Whatever the cause, I plan to have it fixed this weekend.

You can experience the project for yourself at the Rochester Public Library through the end of January.

UPDATE: I went in Saturday morning to diagnose the throttle problem. Current draw does not seem to be the issue. The problem disappeared as I was making some minor tweaks to code, and it’s working fine now. I always get suspicious when that happens. My thanks to the very enthusiastic four-year-old who assisted me with testing.

Looking for details on the throttle?

Schematics, code, and other pertinent info are forthcoming. I think this throttle opens up new opportunities for exhibiting railroads, and I hope you agree. I didn’t get a chance to photograph the boards before installation, so it might be February before a tidy package is ready to post. I’m in the process of learning Fritzing, which is a marvellous tool for documenting electronics projects. Witness this work-in-progress drawing for Chuck’s New Throttle:

Watch this space!