Signalling for Delta Layout

Background

A Model Train Club where I am a member has a "Delta" or "Y" section of tracks as illustrated below.

It is proposed to include signals to indicate the status of the signals on the track. Thus signal "A" would indicate to an approaching train the

status of points 61 and 60. RED if point 61 is against the train, GREEN for straight through and AMBER if point 60 is set to turn.

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Explanation of Track

The complete layout contains many sets of points that can be set/cleared from the master controller. In the section of interest the points are numbered '60', '61' and '63'. (Note point 60 is physically two points that are electrically linked.) Each point contains a relay with two contracts: one will be closed for the point in the Normal position and Open when in the Reverse or Turn position. These relays will be monitored and used to control the train signals 'A'..'H'.

There are two tracks entering from the right passing an area were there are wheat silos. The tracks then merge before again separating with the top (normal) track going to Hardware Lane while the turn or revese sends the train to a another point where the train goes to either Ashland or Pommy Land. With the points numbered '60' linked there will not be any issues with the lower point being incorrectly set.

Trains from Ashland or Pommy land are able to travel to the Silos or the lower Hardware Lane Track while trains on the lower Hardware Lane track may travel to Ashland or Pommy Land.

The basic operation of the signals will be

GREEN The points ahead are in the straight or normal position.

AMBER The points ahead are in the reverse or turn position.

RED The points ahead are against the train. The train must STOP

There is one complication for signals 'A' and 'B' and that is that there are actually 4 options. At point 63 trains can diverge to go to either Ashland or Pommy Land. To allow for this 4th option an additional signal 'C' is included in the layout. By the same reasoning signal 'H' is necessary to indicate the status of point 61 for trains coming from either Ashland or Pommy Land.**

The layout also contains a broad gauge track (5'3" full scale) that crosses the standard gauge track as shown. There will be a switch included to give priority to the Broad Gauge trains.

** (i) As given signals 'C' and 'H' would be inside the length of track defined at each end by points 60.

(ii) Not shown on the diagram but well to the left there is a scissor cross over at Hardware Lane. If signals 'F' and 'G' were moved prior to the crossover there would be four options so signals 'C' and 'H' would need to be located outside the track defined by points 60.

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The Signal Logic

As a first pass the signals can be described with the following equations:

Ag = 61n.60n./BG Aa = 61n.60t./BG Ar = 61t+BG

Bg = 61t.60n./BG Ba = 61t.60t./BG Br = 61n+BG

Cg = 63n Ca = 63t

Dg = 63t.60t./BG Da = 63t.60n Dr = 63n

Eg = 63n.60t./BG Ea = 63n.60n Er = 63t

Fg = 61n.60n./BG Fa = 61t.60n . /BG Fr = 60t+BG

Gg = 60n.63n Ga = 60n.63t Gr = 60t

Hg = 61n./BG Ha = 61t./BG Hr = BG

where signal A is green when point 61 is normal AND point 60 is normal AND not broad gauge. Signal A will be amber when point 61 is normal AND point 60 is turn AND not broad gauge. Signal A is red when point 61 is in the turn position OR the broad gauge is selected

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The Basic Hardware

Inspection of the equations gives:

(i) Four inputs wired to the relay on the points 60, 61, 63 and the broad gauge switch.

(ii) Twenty three outputs wired to Ag through Hr. This suggests 3 8-bit serial shift registers for the signal interface.**

** There are 23 outputs required (there is no red for signal C) and there are six outputs that may be wired directly to an input leaving 17 outputs to be programmed via computer logic. This is one more line than is available with two shift registers.

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