Bill acceptor

A currency detector or currency validator is a device that determines whether banknotes or coins are genuine or counterfeit. These devices are used in many automated machines found in retail kiosks, self checkout machines, arcade gaming machines, payphones, launderette washing machines, car park ticket machines, automatic fare collection machines, railway station ticket machines, and vending machines.

The process involves examining the coins and/or notes that have been inserted, and by using various tests, determining if the currency is counterfeit. Since the parameters are different for each coin or banknote, these detectors must be programmed for each item that they are to accept.

In normal operation, if any item such as a token, coin, note, card or ticket is accepted, it is retained within the machine and it falls into a storage container so that a member of staff can collect it later when he/she empties the machine. If the item is rejected, the machine returns the item to the customer. If a token or coin is rejected, it usually falls into a tray or rolls out of a slot at the bottom where the customer can remove the coin. If a banknote, card or ticket is rejected, it is pushed back out through the machine to allow the customer to remove it from the slot into which it was inserted.

The basic principle for coin detection is to test the physical properties of the coin against known characteristics of acceptable coins. The coin acceptor analyses the coin according to its weight, size, metal composition and/or magnetism, and then sends an appropriate electrical signal via its output connection. The next step is generally performed by the banknote-to-coins exchanger.

Today, sophisticated electronic coin acceptors are in use in some places that, in addition to validating weight and size, also scan the deposited coin using optics and match the image to a pre-defined list, or test the coin's "metallic signature" based on its alloy composition.

Normal circulation coins eventually collect microscopic deposits of dirt, oil and grease from people's fingers. When a coin acceptor is used long enough, thousands of coins rolling along a track will leave enough dirt, oil and grease to be visible. For this reason, the coin acceptor must be cleaned on a regular basis to avoid malfunction. Coin acceptors are modular, so a dirty acceptor can be replaced with a clean unit, preventing downtime. The old unit is then cleaned and refurbished.

...
Wikipedia