A traffic-light system for the modell-railroad

This project has been published in Elektor Magazine 11/2017: EN | DE | NL

It all started when someone asked me to build the electronics for the traffic lights on his model railroad. Sure, a simple task for Arduino. Just add a shield, eventually on a prototype board, and off you go... But wait, some 15 years ago I found on the Internet a nice and simple PLC (Programmable Logic Controller) using a PIC16C84 and a few electronic parts. This thing was simply programmed using a compiler for ladder-diagrams. And even if you think Arduino is too much hankypanky you should be able to construct ladder-diagrams, because they look like a schematic diagram using relais. Now my decision was taken quickly: I will construct a simple PLC-like board which will execute the output of the ladder-compiler using a microcontroller of the PIC family.