Searchlight_Signal

• Searchlight Signal
  • Features
  • Block Diagram
  • Prototype System
  • Dwarf Signal
  • Discussion / Rationale

Searchlight Signal

Searchlight Signal is a project to develop a custom microcontroller-based logic system to manage the signals on my N scale layout. There are two complex "interlocking plant" areas, and a smattering of other signal locations around the design.

The project will provide interlocking control logic for the LED signal heads, based on switch positions, track occupancy, and user (dispatcher) input. The module will (eventually) include OpenLCB connectivity

Features

• Drives G/Y/R LED searchlight-style signal heads
• Drives multi-head, multi-light G/Y/R color light signals
• Accepts turnout position indication from Tam Valley Depot Quad Controllers
• OpenLCB and/or LocoNet and/or DCC control
• Implements logic specific to the layout track diagram
• Programmable

Block Diagram

This is an initial concept block diagram. Subject to frequent and radical change.

(ToDO: Add Block diagram)

Prototype System

As an initial prototype, proof-of-concept, a simple logic board (using 7400-series logic) will be developed to control the dwarf signals on the staging side of the layout.

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In the above drawing, the lines represent tracks. Turnouts are numbered 1-8, and signals are designated with letters A-M (omitting "I"). The tracks marked (EM) and (WM) are the main lines entering the yard, and the tracks marked (ES) and (WS) lead to off-layout staging.

For the prototype, each signal location (A-M) will have a 2-color-light (green/red) dwarf signal installed so as to be visible from a train approaching the associated turnout. Signal aspects will be derived from logic based on the selected turnout positions.

Because at the current stage of layout development all turnouts are under manual control - and to simplify the design of the controller, turnout positions will be indicated by a set of DIP switches on the logic board. This requires that the operator throw TWO switches - the actual turnout switch on the layout and the corresponding DIP switch on the control board - in order to properly set the signals. This is admittedly error-prone. Future versions of the controller will incorporate automatic turnout position sensing, eliminating this dependency.

Track occupancy detection will not be implemented on the prototype system.

Dwarf Signal

For signal indication, the prototype system (and the eventual final system) will use scratchbuilt LED-based 2-color-light dwarf signals. These will be based on the Union Switch & Signal N2 dwarf signal.

These dwarf signals will be constructed using 1.5mm SMT green and red LEDs, and styrene. The LEDs will be connected in a common Anode form, with three wires (Anode, Green Cathode, Red Cathode) leading to the controller.

Discussion / Rationale