Building a universal switch machine control
Mix and match different switch machines/Victor Hand T
he Hudson Division of the New York Central Railroad (HO scale, circa 1950) has grown substan- tially over the past 35 years, particu- larly after its move to a new and larger home a few years ago. Switches were initially powered with commercial, twin-solenoid machines from various manufacturers, but in the 1970’s I ac- quired over 100 surplus rotary relays for a reasonable price and was able to use these relays to build what I consid- ered the ultimate switch machine. It was described in the November, 1977, Model Railroader in an article entitled “The Search for the Perfect Switch Ma- chine.” These switch machines (with some minor improvements) have served me well for many years with lit- tle maintenance.
Capacitor-discharge control Both the rotary relay and twin-sole- noid switch machines already installed on my layout are powered by a capaci- tor-discharge power supply. Many cir- cuits for such power supplies have ap- peared in the model railroad periodicals,
and capacitor-discharge
system supplies and kits are available from Circuitron and Minatronics. In addition, the rotary relay switch ma- chines use a separate 24-volt d.c. power supply to provide power for the holding coil that keeps the relays thrown once they have been activated by the capaci- tor-discharge unit. Switch machines are activated by ei- ther momentary SPDT (single-pole, double throw) toggle switches or push buttons, or both. Many often-used routes (which I call “standard routes”) through complex trackwork can be set up with a single pushbutton that acti- vates a simple diode matrix. The use of diodes for this purpose was first sug- gested by well-known model railroad author Paul Mallery in the 1950’s and has been well documented in the model railroad press and “how to do it” manu- als many times over the years. This control system has a number of advantages: Switches can be thrown from multi-
The author poses by the control panel for his HO scale NYC Hudson Division layout .
RAILROAD MODEL CRAFTSMAN 67
ple locations, or as part of a standard route.
Both rotary relay and twin coil ma-
chines can be actuated with the same controls.
EARL BRECHLIN Auxiliary contacts on the switch ma-
chines can be utilized to route power to frogs and to light panel indicators that tell how switches are set. Rotary relay machines revert to
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