Well if you have stuck with me so far you will have seen how I built the signals, and wired the switching system -but how did I get it all to work together???

The signals are "pulled" by Memory Wire (MW). This is a strange alloy with the property of "shrinking" when it gets hot (actually the crystals change shape). By passing an electric current through it -it shrinks -thus providing the tensile force needed to do this. When the current is off the wire cools and a spring returns this to the unshrunk length. I would advise people attempting this to watch the tension on the return spring as too high -and nothing happens... Here you see a "production" MW actuator. It is a length of Aluminium angle with a tee rocker and a return spring. The link to the signal is from the other arm of the tee bar.

Power at 3 volts is applied to the rocker connection. The length of wire is covered with a length of catheter tubing to retain heat whilst outside. The power is supplied at 12Volts from the main MEDUSA relays and is then regulated to 3 Volts on the unit (a simple Vreg). The same power connection is used to supply the 12Volts to the display panel -again a regulator is used.

The "drawing" is diagrammatic and in no way represents the size of the zones!!! Each set of LEDS has its own connection and links to the MEDUSA system via the D25 connector at the rear. Here is the reverse of the board. (Yes it is not pretty -but since this is the only time anyone is going to see it -I am not bothered...)

If you have followed the ideas so far then you have some idea how the system generates binary numbers (that look like you have pulled the correct signal lever) to actuate the relays to power the MW actuators and light the LEDs.

HOWEVER the one fatal question remains -"So how do you stop the trains???"

The same 12 Volt power is sent to a lineside relay. The NORMALLY CLOSED side of the relays earths out a contact strip before the signal. A 'ski' on the loco detects the voltage present on the strip when the relay opens and powers the strip to 12 Volts and the voltage triggers a reed relay -thus stopping the loco. In real life this opened a valve and put on the brakes.