Delay Signals for Modules

A Signalling System for Modular Layouts.

Preamble

Whereas a normal signalling system uses the track conditions of up to three blocks ahead to determine the setting of the signal, on a module that is part of a collection of randomly connectable layout units, unless there is preplanning and/or specific fixed placement rules, the conditions ahead cannot be determined to allow the setting of the signals.

Rationale

A normal layout signalling system is controlled by the conditions up to 3 blocks ahead of the train. In the case of modular layouts these conditions cannot be known unless modules are purpose designed and interconnected to pass the necessary information between them. This signalling system overcomes the need for special interconnection by automatically controlling the sequence of signal states. This sequence, ‘red to yellow to green’ is controlled by an electronic delay built into the circuit. The timing of each phase can be controlled and will depend on conditions such as train length, operating speeds, scale and other local conditions but which may also include the state of adjacent signals.

In a simple module there might be a signal at the entrance and exit to the module in each direction. The train on entering the module space will activate the entry signal to go through the red-yellow-green sequence. The same will happen when it passes the exit signal. If a train is run on the track in the opposite direction to the signal then the signal will go to red and stay that way until power is removed or the train direction changes back. These simple signal controls allow a realistic and uncomplicated installation of a signalling system in a module or short track environment.

Additional control is available in each signal circuit to hold the aspect at either red or yellow from external switches etc. This means that if there is a set of opposing points ahead of the train then the points will hold the signal at red for driver attention. Or the signal ahead can be connected to this signal to hold yellow while the next signal is at red. A block occupancy detector could also be used in a station module to hold red on the entry signal to the block and it in turn will hold yellow to the preceding signal while a train is stopped at the station.

Each signal driver also has a fixed LED output that can be used for ‘marker’ lights (NZR) or for turnout indications (USA and UK)

Signal Types

The signal driver circuits are designed for LED devices as these give almost maintenance free operation and use little power.

Several types of signal LED drivers can be supplied:-

	Three Aspect, single or dual heads, with marker, yard or main line indicators.
	Searchlight, 2 or 3 lead LED's with single or dual head drivers. (3 lead not in "N" scale)
	Semaphore with servo drive, single wire or 2 wire control are under developement.
	NZR signal logic option for Stop and Proceed, distant repeaters.

This signalling system may be applied to all varieties of prototype that use the above options of signal types.

Connection

Installing a signalling system involves the addition of several wires to the underside of the module to connect electronics to signals to points etc. Keep these wires well secured to the layout so they don’t sag down and get damaged in transport.

Each PCB (one per signal) can be screwed to the underside. Wires to it are soldered to the tags provided. There will be 4 to 8 wires going to each signal. Up to 6 wires to various points position switches, other PCB’s and any other detectors controlling signalling plus the power wires for the required 9 to 12 volt D.C. supply - this is quite separate from the CAB supply in use.

Track connection is by 3 wires that go to each track and to a small isolated track section that is used to detect the passage of the train. This only needs to be 1 - 2 cm long and as the loco wheels pass over it they send a pulse to the signal ‘Spot’ detector input. This will start the signal through its red-yellow-green delay cycle.
Track Cut Cutting the small isolated section is best performed when the track is being laid. At the selected spot turn the track upside down and cut away enough plastic sleepers for the PCB to sit under the rail. With a small saw or cut-off wheel cut halfway through from the bottom of the rail in two places 2cm apart (depending on scale). Now solder a section of PCB to this with cuts made in it the same distance apart and in alignment with the rail cuts. Install the track, solder wires to the ‘spot’ and both rails and then cut through the rest of the rail from the top. You can fill the gap with epoxy and smooth it off to the correct profile. Doing it this way ensures that the isolated section is in exact alignment with the top of the other rails for correct operation.

Track alteration on installed track is a little harder. Proceed by marking out where the cuts are to be made, solder a wire to this piece of track and feed it through a nearby hole to the underside. Cut away sufficient sleeper material to allow a puddle of epoxy to be poured under the track for 2cm each side of the section to be cut. You could reinforce this with fibreglass or cloth poked under the rail. Make sure it covers the lower rail flanges. When the epoxy is hardened cut the rail through (a cut-off wheel is best) avoid getting the track too hot which might soften the epoxy and result in misalignment. Wash out any metal swarf with alcohol and test with a meter that no connection exists between the short isolated section and the main rails. Make the other rail connections.

Correct Track connection is that as the train approaches the signal
The positive rail is on the right and the spot rail is on the right:-

the positive (right) rail to the ‘+R’ tag on the PCB;
the spot to the ‘S’ tag;
the opposite (negative rail) to the ‘-R‘ tag;

Signal connections will depend on the type in use.
The LED's in the three aspect type of signal are connected with all anodes common.

3 aspect signals - connect common to ‘c’ and the others to ‘r’,’y’,’g’
searchlight 2 lead - connect leads to ‘r’ and ‘g’ terminals (reverse if incorrect)
searchlight 3 lead - connect leads to ‘r’, ‘c’ and ‘g’ (‘c’ is the cathode/centreLED lead wire)
marker LED connects to ‘m+’ and 'gnd‘ (ground)
(note the ‘LED gnd‘ of the marker may be connected to a points switch then to the 'gnd' to indicate a turnout condition for USA prototype operation)

Power On

If the above connections have all been made correctly then at power on all should work. The signals at power on will normally go through a red-yellow-green sequence and then be ready for operation.

The Delay

The delay time is set at build time by inserting the correct resistance in circuit. The resistance required is calculated by the time required. For each second of delay add 100,000 ohms of resistance. So for a 10 second delay use a 1megohm resistor.

What delay time to use will depend on a number of things.

How long it takes for the longest train being used to pass the signal plus some.
If there is a station etc just ahead of the signal that the train might stop at.
If you are linking to other signals to control the yellow or red aspects.

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