[Alex] wrote in to let us know he just completed a pretty major upgrade to his PopCARD RFID vending machine system. You may remember that earlier this year he added an Arduino based RFID reader to a soda machine so that thirsty patrons could pay with plastic instead of cold hard cash. That system worked, but at the beginning of the video after the break [Alex] goes over some of its flaws. There was a button to add cash from the card to the machine in $1 increments, rather than the system just knowing how much to charge you. Also, if you accidentally selected something that was out of stock you were out of luck and were charged anyway.
The new system does away with the button, and knows what product is sold out. The control hardware was upgraded to an Arduino mega to gain extra I/O pins. The device now sits in between the machine’s buttons and its own controller. When cash is used, the Arduino sits passively and lets the machine do its thing. But when a card is scanned, it takes over control of the buttons, sensing your selection, then simulating coin and button presses to vend accordingly. The new setup also uses an Ethernet shield which allows [Alex] to tell what items are running low without being at the machine itself.