When I was younger, I wanted my model railway to have signals. But not just signals set by hand: I wanted them set automatically as trains went past, when the track ahead had a point set against it etc. The technology just wasn't there 30 years ago.

When I started again into this - about 10 years ago now - I looked into DCC as a way to control trains and realised that now, all of the information to work out a signal aspect was available on the command bus. The idea of automatic signal control started there, but I has to learn LocoNet and DCC first.

There aren't many signals on the railway yet: but there will be. It's a modern image railway, so there will be colour light signals, set automatically as trains move. When a train passes a signal mast, the signal will go red; when the points in the track ahead aren't set correctly, the signal will go red. CML Electronics' SIGM20 does all this, and more.

The SIGM20 is fundamentally a LocoNet device, rather than a DCC device. All the information to work out the signal aspect is on LocoNet. It knows the positions of the points; it knows what track sections are occupied; it knows what other signals are set to. The SIGM20 hoovers up this information, and works out what each signal should be set to.

Each SIGM20 can drive 8 LED signals. The boards will be distributed around the railway, as near as possible to the signal masts.
The new DAC20 extends automatic signal control to semaphore signals too. We may have one or two semaphore signals in the engine shed at Portsmouth, just for fun!

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