In order to correctly display the status of any given situation, we need a way of knowing what to display.
This page provides a brief overview of some basic techniques we use to determine what the status of a signal should be.
A system for detecting when a train is in a block or on a certain section of track is necessary. For current type detection, the track must be gaped on one or more rails, according to what the block detector manufacturer advises for their system. There is also block detection that uses photo-cells or IR type devices. There are different types to choose from and each manufacturer has their own version and style, so some research is in order to see which one will work with the DCC system that you have.
Turnout Position Detection
You should know what position your turnouts are in also, because this affects the signal aspect or color. This can be done by wiring the auxiliary switches on a turnout machine to an input of some type, or some systems will use the same computer signal that is sent to the DCC turnout controller when throwing a turnout.
The signal board takes the computer signal and makes the signals display the aspects or colors that the program says they should be. Signal wiring can be intense. Some systems are modularized to make the wiring easier.
While this is optional, having a computer control signals has many advantages.
The computer software or program controls the system.
It looks at the blocks, if occupied or not; looks at the position of the turnouts; and looks at any other sensor indications that are being sent to the computer. The Logic in the program takes all of these inputs, tests them with the program logic, and then sends the appropriate commands to the signal board to light the signals with their proper aspects or colors. The computer panel shown below was designed using JMRI Panel Pro. JMRI also provides the logic for everything to work. When turnouts are thrown, blocks occupied by a train, and the signals change, the display icons change to reflect these events. This panel is currently being built and modified as more block detection and signals are added to the railroad. The center window is the most complete.