kitty door it is not, but this RFID-equipped soda machine is by far one of the most practical DIY projects we've seen in sometime. A Canadian tinkerer picked up this pop pusher a few years back, and has been using it to sling drinks in his building ever since. Unfortunately, finding the right change to feed the machine proved an issue for his neighbors, so he did what any logical hacker would do, and built in a contactless payment system. Using an Arduino, an Ethernet shield, an LCD screen, and an RFID reader, he created a system that allows customers to swipe a card and easily add funds from an online account. Best of all, every time you press that little blue button you get a Mario Bros. sample. Big ups, PopCARD. Video after the break.