Instructables user 'skipped' has documented something quite different - how to read the data from a coin acceptor. Apparently these are cheaply available on eBay, which opens up all sorts of possibilities: vending machines, over-engineered money boxes, pay toilets and more. Apart from documenting how the coin acceptors can be programmed to measure and report on various coin sizes, he has described how to use this data using an Arduino and also via PC with MS Express 2010.
To minimise the space required for such a project, a Freetronics LeoStick would fit snugly under the coin acceptor:
Apart from being one of the smallest Arduino-compatibles on the market with USB, it also has an onboard RGB LED and piezo which can be used a knock sensor and various tune and sound effects. Plus you can add extra circuitry with the matching protostick! For more information and to order, click here.