Signalling and Track Circuits

[Inversnecky]

It’s been about forty years since I had a model railway, all pre DCC. Things are a lot more sophisticated these days, but I was wondering, can track circuits with automatically controlled colour light signals be recreated on a model railway, so that a train passing a signal turns it red, with the previous ones turning yellow, double yellow and green in turn?

 

[4COR]

Absolutely - and it's much easier with DCC to ensure block detection works properly (use resistive wheelsets, or lighting in coaches) even where the train isn't moving, or where there is rolling stock with no loco which is trickier with conventional DC layouts. The alternative way of triggering a change to red, and possibly more useful for non-automatic signals is to use IR detection to detect the passing of a train past the signal in question (you could use this with a latching relay of some sort to hold it at red).

To change the signal in the rear, one way is to use relays to change the aspect (you'd sort of have a chain of linked relays) - this would actually work even with signals that weren't interlocked with the block detection. Brian Lambert's page (https://brian-lambert.co.uk/Electrical-Page-3.html#signalling) has a diagram showing linked switches - if you imagine these being relays instead linked into the block detection, it gives an idea of how it might be done.

I'm sure there are also commercial products to do this as well, or for really complicated situations, you could even consider using something like an arduino and code up the logic and use the various IO pins to sense/control the signals. You could also use the auxiliary switches on point motors to interlock eg facing or trailing points with protecting signals or junction indicators as well.

 

[Inversnecky]

Thank you. Reading that makes me realise how much knowledge of electrical wiring I’ve lost over the years.