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MODEL TRAIN SWITCH CONTROL
VIA PC OR PIC
BY DAN GRAVATT
This is a project I wanted to
do many years ago when I
was spending a lot of time
and money on my model
railroad. I was disappointed
by the big, clunky electrical
controllers which operated
the track switches, and I
wanted to have something
smaller and more elegant to
do the job. A computer
control system would have
been ideal, but I never got
around to designing one. Many years and several designs later, I have come
up with two versions of the control system: one PC-based and one PIC-based.
Both designs work on the same basic principles. The
PC-based system has many possibilities for displaying
track switch status, at the expense of needing a dedicated
computer at your model railroad control station. The
PIC-based system is a stand-alone direct replacement
for the manual electrical controllers and has a simple
three-button user interface.
There are other control systems commercially
available for track switch control, mostly based on the
Digital Command and Control (DCC) standard. DCC
was originally designed to control model locomotives by
sending power and data through the tracks, allowing
multiple DCC-enabled locomotives on the same track to
do different things. Add-on modules for DCC are available
to control track switches, but they are fairly expensive
and won’t work without a master DCC system. My
control system will work just fine on either DCC or
non-DCC model railroads as it does not depend on any
other hardware.
Anatomy of a Track Switch
The most common model railroad track switches —
often called snap switches — are electromagnetically
actuated by two solenoid coils:
one moving the track to the
“straight ahead” position and the
other for the “turn” position
(Figure 1). Reversing the polarity
■ FIGURE 1. Track switch solenoid.
When attached to the railroad
track, the lever on the end of the
solenoid moves the track section
back and forth.
38
August 2008
