What about sem­a­phores?

Model Rail (UK) - - Workbench -

Semaphore sig­nals are nor­mally set at dan­ger and only change to clear when an ap­proach­ing train is to pass them. In­ter­est­ingly, colour light sig­nals are nor­mally at clear un­less a train has just passed, or the next sig­nal up the line is at dan­ger. The sim­plest way to repli­cate semaphore op­er­a­tion is to have a de­tec­tor be­fore the sig­nal which will change the sig­nal to clear and also start a timer which, on tim­ing out, will change the sig­nal back to dan­ger. A more so­phis­ti­cated method is to have a de­tec­tor be­fore the sig­nal to change the sig­nal to clear and a sec­ond de­tec­tor af­ter the sig­nal to re­turn it to dan­ger. The IRDASC-1, 2, 3 and DSS work in this way. In fact, the re­turn to dan­ger de­tec­tor is also used as the ‘set to clear’ de­tec­tor for the next sig­nal along the line. Dapol’s sig­nals fea­ture a mech­a­nism that moves the sig­nal arm, op­er­ated by a tog­gle switch which changes the sig­nal be­tween clear and dan­ger. Heath­cote Elec­tron­ics’ Semaphore Se­quencer can con­trol Dapol sig­nals, and is po­si­tioned be­fore the sig­nal. When the train reaches the Semaphore Se­quencer, it closes a con­tact for one sec­ond and starts its timer. At the end of the tim­ing in­ter­val the con­tact closes for one sec­ond, and the sig­nal re­turns to dan­ger. Heath­cote Elec­tron­ics’ boards come with con­trol ser­vos, in­clud­ing the Bounc­ing Semaphore Con­troller, which gives the sig­nal arm its char­ac­ter­is­tic bounce.

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