Automatic car parking system | PLC project demo

This is a little model of an automatic car parking system I've built and designed some years ago as a university project, for the Master of Science in Computer Engineering. I used a Zelio Logic PLC and two old 5-wire stepper motors. The motor controllers cards were also built by me (a lot of soldering, by the way). A car, placed in a starting position, is transported and parked into a free parking lot, selectable by the user via the PLC's front buttons. The process can be reversed, selecting the parked car to be retrieved. The PLC executes a state machine I wrote in IEC 61131-3 Ladder. An inductive proximity sensor provides feedback to the PLC. Two electromechanical relays control the direction of rotation of the two motors. The two motor controllers are composed of a pulse generator and an indexer (flip-flops and XOR ports), that distributes the pulses to 4 power transistors. The pulse frequency can be changed using a potentiometer. The duty cycle is fixed by the capacitors. You can find a longer and more detailed video here:    • Automatic car parking system controlled by...   Giorgio Distefano disjorge@gmail.com Dept. of Electrical, Electronic and Computer Engineering (DIEEI). University of Catania (UniCT), Italy, 2015.