Apr 2016

Arduino Knobs

This is one of those “interim posts” I mentioned at the beginning of the year, posts where I don’t have something yet in a state where I can really talk about it, so I focus in on one detail that’s been taking a lot of my time, as a form of update. But today’s topic, rotary controls for computer-based systems, is a generally useful one, so I don’t think you’ll count this post a waste of time. At least not if you are interested in this aspect of the hobby.

A rotary control, or knob, is a control that can select a continuous range of states arranged in a circle, such as the volume knob on a stereo. Any rotary control can also be laid out as a linear one, simply by straightening out the underlying mechanism (they have to be designed that way, but often are). In schematic diagrams, a linear symbol is typically used to describe either kind, since from an electrical perspective they are identical.

In model railroading the most common application for this kind of control is a throttle. My first power pack, an ultra-cheap kit pack from Tyco, had a linear control (actually it was rotary inside the box, but the lever sticking out the side looked linear to me). Later, my first good DC power pack (my MRC 501, which you can see on my Power Pack Testing page) used a knob, albeit a simple one.

But today, I need a continuously variable control for a digital system, an Arduino to be specific. And yes, it’s for a throttle, but I’m not going to talk about the actual project I’m working on, as it’s still in the early design stages and there’s nothing much to say yet. Instead, I’m going to talk about the various options for this one control, and then go into more detail about the one I’m using, seen in the photo above attached to an AdaFruit Feather M0 Proto (a type of Arduino) for testing.

Ochanomizu Station Signals

JR’s Ochanomizu Station (御茶ノ水駅, Ochanomizu-eki) is an important part of my modeling plans. As seen in the photo above, it’s a mix of old and new architecture. And it’s built along the bank of the Kanda river (the temporary construction platform on the right is actually erected over the river). It’s slightly below street level, with a city skyline climbing up behind it from a front rank of buildings around six stories in height to taller ones further away. It’s pretty much ideal as a modeling subject visually, and it sits at the junction of two busy lines, so there is a lot of activity.

I have been trying to figure out how the signals here and nearby work so that I can include a reasonable subset in my model, but photos in and around the station tend to focus on other subjects than signals for some reason. Thanks to one of my readers, George Roberts, I now have a number of photographs taken around the station and adjacent areas that include these signals (and other interesting details).