Model Railroad

Reversing Loop Switch Machine Controller

For Stall Motor Switch Machines

  This circuit is for a switch machine controller for reversing loops. The circuit is light activated and designed to drive stall type switch machines.

Switch Machine Controller Features

Not For Twin Coil Switch Machines

General Notes For The Reversing Loop Switch Controller

Installation Schematic

  Below is an installation schematic for the reversing loop circuit. The optional relay is also shown on the schematic.


Reverse Loop Switch Machine Controller Parts List

Qty - CIRCUIT PART - DigiKey Part
- - Semiconductors - -
1 - IC 1A, B - LM393NFS-ND
1 - IC 2A, B - 497-1965-5-ND
3 - Q1, 2, 3 - 160-1988-ND
4 - D1, 2, 3, 4 - 1N4148DICT-ND
1 - D7 - 1N4001DICT-ND
- - Resistors - -
2 - R1, 2 - 470KQBK
4 - R3, 4, 13, 14 - 10KQBK
1 - R5 - 100KQBK
- - Capacitors - Capacitors
1 - C2 - P5177-ND
2 - C3, 7 - P5174-ND
1 - C4 - P5181-ND
- - Terminal Blocks - -
1 - 2 Positions - 3.5mm - ED2635-ND
3 - 3 Positions - 3.5mm - ED2636-ND

Reverse Loop Switch Machine Controller - Dogbone Track Diagram

  The polarity control relay is switched OFF when Q1 is covered by the train and switched ON when Q2 is covered by the train.

  The switch machines operate at together but in opposite directions. The turnouts move to the R position when the phototransistor nearest them is covered by a train.

  One set of contacts from one switch machine is used so that the system remembers its last position when the power is applied to the circuit. Also, one set of contacts from each switch machine can be used for frog polarity control.

Twin Coil Switch Machines

  It would be less costly and less complicated to use a slow motion switch machines rather than twin coil machines. Slow motion machines have auxiliary contacts built into them and can move the turnout to the proper position when power is applied to the circuit.

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.


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07 April, 2019