For some time now, the Corridor membership has wanted to set up signalling on the layout, but I only got a chance to dig into the circuitry design end of it a few months ago. Someone from Free-Mo had suggested MSS (Modular Signal System), and I read into the technical docs for it; but ultimately chose to go a parallel but independent route. There are some specific reasons for this choice, notably that MSS requires separate RJ45 cabling for each track, plus some frustration with their design architecture w/regard to "crossover" nodes and cabling being used for modules with straight track, and "cascade" block-break nodes being used for modules with actual track crossovers. (MSS block breaks are also fixed to specific modules with the correct hardware installed.) With our four-track mainline, times 40 modules, that's 160 each cables we would need to transport and hook up correctly at every show to use MSS, not to mention the fact that there are no four-track cascade nodes available for our interlockings, which are all of varying designs. MSS also requires bi-directional implementation on every track signallized, while the corridor itself only uses bidirectional signalling on the center two tracks, with the outer two tracks being single-direction only.
So for the Corridor Signal System (or CSS if you like), I reduced the network cabling down to two cables per joint (saving us 80 connections), and streamlined the logic states carried on the network bus. All our nodes and cables are straight-through (and not "crossover"), and we only use cascade cabling at block joints, which can be placed at any module joint as needed. Using off-the-shelf occupancy detection would have cost about $80 per module just for the detectors, not including the Node board, so I designed our four-track Universal nodes with occupancy detection right on the board.
These boards have been a great decision from the get-go, and are really easy to install on most modules. They're also really reliable on the detection side, as I use a single 10k resistor load to test each detector channel.
The next step from there was to add the display layer, handled by separate boards for each signal installation. I designed up separate board types for Home and Intermediate signals, as Home signals use upper and lower heads, while Intermediate signals are upper-head only. (ground dwarf signals can be run by the Intermediate board if it's populated for that, and PL5 Pedestal signals can be run by the Home board and a diode matrix on the output side.)
Here's the chart of most of the aspects that operators will encounter on the layout:
Intermediate boards will also display Advance Approach (flashing approach/flashing yellow), and Home signals may also display Restricting if the route selected takes the train into unsignalled track.
Clockwise: A DT4 universal detector node, a Home display board, and an Intermediate display board:
Version 2 of the Home board, now with cheater display for troubleshooting, showing Approach Medium:
Medium Clear:
Approach Slow:
Here's what an installation for one end of a full interlocking, looks like:
Note that this has three full Home signals on a bridge, and one ground dwarf protecting wrong-way movements on track 4.
All this work would be useless without some actual signals though, so drool over these:
I'll have more photos as the project continues.
--Drew
