This was fun writing! If I should do more, follow and let me know!

Yet, there’s plenty of life on those ol’ fish tank relays.

They’ll likely stick around on the Piccadilly Line up until they get swapped out for a new signalling system after it gets its shiny new trains.

The two won’t come together, so plenty of times for the new trains to play with old tech ❤️

And now, some clever clogs are trying to take that further and send interlocking up into the cloud

www.mobility.siemens.com/global/en/po...

Whilst the tech is decades old and is still being used today, already it’s on its way out.

Current iterations use Solid State Interlocking that use banks of circuit boards, like this!

These fish tank relays have a bunch of connecting points called contacts where its output can be part of a larger circuit.

Hook up enough of them and you can run plenty of signalling logic on them.

If the relays for track circuits (chunks of track) A, B, C are unoccupied, then way is clear!

But what do they do?

In short, they’re just switches!

They turn on or off based on a complicated set of logic conditions.

Example: a points indication relay will energise (switch on) if a set of points is thrown, whilst a signal relay would energise if everything is ok for a signal to go green!

And I do pretty much mean nearly all!

Here are some in Acton Town Relay Room. Round the corner from a maintenance facility designed to keep them running.

(This photo was taken by yours truly during a night of testing)

They’re letting go of a diamond.

Thinking of ya buddy. Whoever you land with will be gaining the toppest of lads