Please, check out OTIMCON https://github.com/stajp/otimcon - Arduino RFID based open source timing control. It has everything written below, and it's based on cheap components easily bought on eBay and similar websites.
OPORCON ver. 2 is under way. After looking at David's nice OPORCON set and his improvements, and some ideas from others, I chose to start on OPORCON 2, to update my current system.
OPORCON2 will still be OPORCON1 compatible. By now, 3 slightly different OPORCON boards (my OPORCON 1, Bjarne's and David's) exist, but the data on chips is compatible in all systems. As I wish to extend my collection, OPORCON2 must (and will be OPORCON1) compatible.
Considerations on OPORCON2:
Ideas to contemplate: