Museum Signal Post Display
The display board consists of a track diagram with three colour light signal posts spaced along the track. As the train, indicated by a pair of LEDs, moves from section to section, the three aspect signals respond appropriately.
Normally, when the sections shown are clear of trains all three signals show a green aspect.
When the train moves past the first signal, that signal changes to red.
When the train moves on, the second signal that it has just passed turns red and the first signal changes from red to amber.
When the train moves past the third signal, it turns red, the second signal turns amber and the first signal reverts to green.
The actual signal post lights follow the sequence shown by the first signal on the display board.
6 Volt Supply
The LEDs in the display board are powered from a 6 volt supply. Switching the unit on at the display board operates the relay in the 6 volt unit, which in turn switches on the mains to provide a 6 volt AC supply to the control relay set. The AC is rectified in the relay set.
The Display Board
The Display Board holds the on/off switch, the auto/manual switch and the step on button as well as the LEDs representing the signal lights.
The LEDs are connected via a diode matrix to four input lines receiving 6 volts DC from the control relay set. One of these lines will be active at any one time by being connected via the wiper and arc on a stepping uniselector. The matrix ensures that the correct LEDs light for that particular active line.
The main lamps in the actual signal post are also operated in the same sequence as the first post on the board. 50 volts are supplied by a separate wiper and arc on the stepping uniselector.
The Control Relay Set
The Control Relay Set is started by an earth operating relay ST. This earth comes from the Display Board on/off switch.
Earth pulses can now be derived from the 30 second clock if auto is selected on the display board. Relay MN remains released.
When the first clock pulse is received, relay PX operates and at PX2 pre connects the PY relay. PY is held short circuit by the clock pulse, but when the pulse ceases and the short circuit is removed, relay PY operates and holds to ST5. PY1 then connects the next clock pulse to relay SA.
When the next clock pulse, or the first step on pulse is received, relay SA operates.
This sequence continues, driving the wipers around the arcs and changing the display. There are only four conditions to be displayed so these four conditions are strapped around the uniselector bank six times. When the uniselector reaches outlet 0 (home) it drives again to outlet 1 to continue the sequence.
Switching off at the Display Board releases relay ST which in turn releases all relays in the control relay set and 6 volt unit.
The following diagrams are available in PDF form :