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This section describes the architecture of the DCC system - particularly how the track is powered.
The railway's wiring rules are available here. These are likely to be updated as progress is made!
System Architecture
The power to the rails is zoned and has block detection. This is a little more complicated than the minimum DCC installation and is worth expanding on.
The principal elements of this are expanded in later pages on this site, but briefly:
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Track power comes from boosters. I have used three: two power the track, and a third powers accessory devices. This ensures adequate power is available; it also ensures that accessory devices are always powered, even if there is a track short.
- PM42 power isolators break the track into different Power Zones.
The PM42s act as circuit breakers and ensure that if a short occurs,
power is only removed from the local area and not from the whole layout.
- PM42 cells are also used as Autoreversers for reverse
loops. Cells used in this way also have a power isolator in their
power feed.
- BDL168s are used for Block Detection. This ensures that
train movements can be followed around the railway.
- Track sections powered by a PM42 cell are "Double Gapped"
at either end of the zones. Each power zone is completely isolated
from the next. This is known as "Direct Home" wiring.
- Because of the block detection, the track is powered by a large number of wires each of which is current limited by a PM42. there is no single power "Bus".
LocoNet Wiring
In principle, each LocoNet device comes with two telephone style connectors; the wires simply get daisy chained together. However that isn't the neatest solution, and will make debugging difficult. What I chose to do was to split the LocoNet up into sections, with a "bus" joining the sections with wires into different areas "tee"d off from the bus. That way, any one area can quickly be isolated for maintenance or if a board fails.
In areas where humans are likely to operate trains, I have added UP-5 panels to plug in throttles. These are low costs and a lot tidier that some alternatives.
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The main command bus is LocoNet. This uses 6 conductor telephone-style wire with RJ12 crimp connectors. There is a convention for the wiring: although it doesn't matter if a cable is "crossed over", it will be easier to debug if the colour coding is consistent.
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To split the LocoNet into sections, I used the "UTP" panel from Tony's Train Exchange. This is designed for walkaround throttles, but unlike the UP-5 it does fully connect all six wires. It is possible to use telephone connectors for this instead. However, I've had a lot of poor experiences with telephone connectors in the past. This picture shows two UTP panels in one area where a lot of separate connections will be needed. Note I've marked the LocoNet "backplane" cable with "in" (towards the command station) and "out (toward the next area on the railway).
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At my workbench, I've connected up the signals I'll need for testing electronics and locos. Wired into the box on the wall are:
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