A currency detector or currency validator is a device that determines whether notes or coins are genuine or counterfeit. These devices are used in a wide range of automated machines, such as retail kiosks, supermarket self checkout machines, arcade gaming machines, payphones, launderette washing machines, car park ticket machines, automatic fare collection machines, public transport ticket machines, and vending machines. The process involves examining the coins and/or notes that have been inserted into the machine, and conducts various tests to determine if the currency is counterfeit. Because the parameters are different for each coin or note, these currency acceptors must be correctly programmed for each item to be accepted. In normal operation, if any item such as a coin, banknote, card or ticket is accepted, it is retained within the machine and it falls into a storage container to allow a member of staff to collect it later when emptying the machine. If the item is rejected, the machine returns the item to the customer. If a 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 ejected out of the machine so that the customer can remove it from the slot into which it was inserted. Coin acceptors The basic principle for coin detection is to test the physical properties of the coin against known characteristics of acceptable coins. The coin acceptor identifies the coin according to its mass, size, diameter, thickness, 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 being used in some places that, in addition to examining the mass, weight and size, also scan the inserted coin using optical laser beams and match the image to a pre-defined list, or test the coin's "metallic signature" based on its metallic composition. Normal circulation coins eventually collect microscopic particles of dirt, dust, oil and grease from people's fingers. When a coin acceptor is used for a long time, thousands of coins rolling along a track will leave enough dirt, dust, oil and grease to be visible. As a consequence of this, the coin acceptor must be cleaned properly on a regular basis to prevent malfunction or damage. Coin acceptors are