Siemens LOGO based realistic Finnish signaling, interlocking and automatic train control on miniature railway.
I did this on my school; this was my graduate work.
I built everything, except PIKO tracks, switches, switch electric turnings, grass mat, the Siemens ER20-diesel loco and two german Esslingen-passenger wagons. Those were bought from miniature railway shop, but track ballast, all signals, interlocking box, level crossing signalling and "bell", automatic train path based control, signal relay groups, trackside sensors and their relays, switch turning control and locking, and all programming on LOGO:s were built and assembled together by me. Whole project took 2 months and 1700 euros.
There is 5 Siemens LOGO:s on the project, two on interlocking device, one on level crossing control, one on automatic train path based control, and one on switch turning and locking.
Three out of five programs on logics are larger than 125 blocks (maximum: 130 blocks on LOGO), and two of them are already on maximum.
There isn't any Digital Command Control (DCC) on this track, train is solely controlled by "analog" automatic train path based control, and it controls the voltage on the rails with four contactors. There is power supply of old computer supplying the voltage on the rails. 5 volts is the maximum, and by adjustable resistor and four contactors it can be dropped to 2,5 volts and reversed if necessary.

Signalling is replicating Finnish railway signalling from 1990's. The signalling was not aestethically complete. Signalling was modelled by functions of Finnish railway signalling system, see Wikipedia article.