Q: I am the only operator. There will be no others. I wish to use block detection for signaling. However, I find that I cannot use the BD4s in the way I thought they could be used. My question, must I divide my simple layout into blocks (which DCC says you don't really need) in order to use the BD4's and SE8C together?
A small basic layout can be operated in the DCC environment without dividing the railroad up into power districts. In this scenario, you will use one command station/booster to power the entire layout.
As your power consumption grows with the addition of more locomotives, you sould divide the railroad up into power districts, each with its own booster and transformer. Power districts are used to add power to the layout and NOT for controlling locomotives or the layout. The control is handled by LocoNet that links the components together into a Complete Train Control system.
Alternatively, you may find it to be better to divide a power district into power sub-districts using a PM42 to control the power sub-districts without adding boosters for more power. In this case the objective is to improve operation by managing interruptions caused by short circuits.
One example would have the main line as one power district, the engine terminal as a second power district, the switching yard as the third district and the fourth power district providing power to turnout motors. Each power district has its own booster in this scenario and all the components are connected via LocoNet. If a short circuit happens in one district, operation in other power districts will not be affected.
Signaling and detection sections.
The whole notion of signaling is to protect the movement of trains. This means that each train location must be identified. The real railroads and model railroads both do it the same way, they measure the flow of current between the two rails. In the case of the real railroad, the presence of any car or locomotive completes the circuit between the two rails, giving indication of the presence of a train. The model railroad uses the same principal, with the BD4 detecting the presence of a train and conveying that information to the control system.
As with the real railroads, you must divide your model railroad up into signaling or detection sections which reflect the operation of the railroad. Such a section should be as long as your longest train, but may be smaller as circumstances dictate. For example, where two tracks cross could be a very small but important signaling/detection section, since only one train should occupy the crossing at a time.
As an example, there is a very familiar track plan that fits on a 4' x 8' space in H0. This plan has two main lines, a passing siding / yard switching lead, a yard, two long sidings and an engine turntable. Typically, each main line would be divided up into at least four, or more likely, five sections. The switching lead would have two track sections.
And, perhaps, the long sidings would have a section each. The yard would most likely not have the need for signaling or detection, but would have a signal at the point where the yard connects to the switching lead. The engine terminal would not need detection either, since it is connected first to the signaled yard.
The subject of railroad signaling is a complicated one, one that requires some forethought prior to actually installing the system. In return, you have a model railroad which accurately captures the look and feel of the real railroad.