How does a vending machine read dollar bills?
As we do with many of our technology-related questions, we consulted a fantastic resource called How Stuff Works. After some hunting and pecking, we found a relevant question about dollar bill changers that discusses the mechanics of automated currency identification. While vending machines use a variety of methods to read bills, they check four different characteristics used to verify paper money: • Bills are printed with magnetic ink, and different denominations generate distinctive magnetic fields. • Bills have different conductivities (the rate at which they can conduct low levels of electricity). • Ultraviolet scanning technology can determine the different fluorescent properties of bills. • Digital cameras can reference the optical patterns in bills with a database of authentic patterns. A vending machine has to veri
