Signals on my layout and Crossroads railroad club
I have built an signal system that will indicate block occupancy, turnout position and has input from a dispatcher if desired to operate three color signals. The signals are home built using commercial signal heads. For entering a passing siding, a three head (GYR) for the main over a two head (YR) for entering the siding. To leave a passing siding, each track has a three head signal (GYR). Separate blocks have three heads in both directions. The occupancy detectors are Bruce Chubb's Optimized detectors form Model Railroader about 10 years ago. The only part of his system that I used was the detector and the detector mother board, not the computer interface. As my layout was DC at the time, the detectors use the voltage drop across diodes to indicate a train in the block. This has worked OK with DCC, but it is necessary to control the current through the track and detector either with 6 amp diodes (5 amp power supply) or a light bulb to limit the current. If starting out with Dcc, He had a transformer type detector that can be used. These detectors are available built up or making your own by buying the printed circuit boards, and parts from an electronic supplier. (Jameco, Mouser etc Radio Shack is much too expensive). A power supply is needed for the detectors and the easiest solution is an old computer power supply which will supply the +12, -12 and 5 volts needed to power the system. Add a led and you can show occupied blocks on a dispatcher panel. I feel that this type of occupancy detection is better than photo- detection. Infrared photo detection is useful to show that a train has passed a certain point and is clear of a switch ect. I use both on my layout.
The next part of the system is the operation of the signals. The output of the detector is a transistor that is turned on and off by the train. This is one input. The position of the turnout is another input. Another is the dispatcher desire. This means at least three inputs are need to clear for the signal to go either Y or G rather than red. To indicate a green two block ahead must be clear, if only one block the signal is yellow. Each signal head (not signal) must have a circuit to control the aspects. Several years ago an article in MR described a transistor circuit to operate the signals, however it used a lot of current and would not always turn off the LEDs. A model railroader in Canada, Rob Paisley, revised the circuits and developed others not only for signals but for crossing gates, and many other Model railroad application ( including photo detection etc). He currently has on his web site (http://home.cogeco.ca/~rpaisley4/3LightSignala2012.html) a 3-Light - Model Railroad Signal Driver that can be used to drive 3 light, searchlight and position signals, either common cathode or common anode connections. Circuit boards are available . On my layout, I used one of his circuits call "Not so simple 3 light signal" which used a LM339 IC op amp to drive the outputs to the signal head. I used Radio Shack circuit boards. each with 2 circuits. This has worked very well on both my layout and our club layout. However. it is not listed in Rob's current circuits. It was not suitable for searchlight signals, but the new driver is.
A complete signal system adds a lot to the layout, and I believe is worth the time and expense. Doing it yourself is another way to enjoy the hobby. As I am retired, a commercial system is beyond my reach, so doing it this way made it possible.
Bill
