The bit about signals
The way I did it
Express Escape
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Two aspect signal lamps with only two wires. When fed with a positive supply they show red and when fed with a negative supply they show green. The two L.E.D.s are connected together but opposite anodes, (just the red and green in picture below). One side is connected to the brass tube and the other side is connected to a resistor of about 2kr which is connected to a length of wire which goes down through the tube. All soldered and glued to the tube, the black bit,s are made from card and drinking straws. For temporary or dummy situations the bottom of the tube is connected to one side of the track and the wire is connected to the other. Hopefully when the train approaches the lights they will be green and when travelling in from the other direction the lights will be red |
Three aspect lights
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Taking this ideal a bit further I put three L,E,D,s together as shown and connected them to a logic chip, More on that later. The LEDs are soldered closely together and joined to three bits of small single core insulated wire about a foot long. Note no limiting resistor (yet). The three wires twisted together makes a strong enough post, cover it with tape and paint accordingly. The top end is fitted out with a piece of card and bits of drinking straw, then painted black. Poke the wires down through the base board and connect to the logic thingy that is described below. To make things a bit easier to draw I left out the power supply connections but these can be worked out in the normal way. |
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Simple logic controller using one chip per signal post | |||
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This controller normally shows a green light with no inputs. An input on YS sent back from the distant signal shows yellow and an input on RS from a local source overrides all and shows a red light. The RS input is also returned back the preceding signal YS connection. The RS input comes from point contacts and/or block system. | |
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This is the truth table for HEF4001B. the chip I used in the experimental stage. It was mounted on a bit of vero board directly under the signal. The power came through a resistor from 24v DC and was regulated by the LEDs to something small, it worked OK but I put the output restors in anyway to bring the working voltage up to about 12v |
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Resistors on the input are there to hold the gate to ground when no inputs are present, Inputs from any supply rail need limiting resistors , this is not the proper way to do it but it's cheap and all mine still work. All values have been left out as these are not very critcal and may be changed to suit the supply voltage.
This circuit is for the HEF4001B , if it is to work with any other chip it will need to be modified. This is only a rough description, but if you would like more details then please email me.
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