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A currency detector is a device that determines if a piece of currency is, or is not, counterfeit. These devices are used in vending machines that accept payment and dispense a product to a customer. They are also used in change machines and in slot machines.
The basic process involves looking at the currency that has been inserted and by using various tests, determine if the currency is counterfeit. Since the parameters are different for each coin or paper money, these detectors must be programmed for each item that they need to accept.
In operation, if the item is accepted it is retained by the machine and placed in a storage device. If the item is rejected, the machine returns the item. If it is a coin, it usually drops into a container for the customer to take back. If it is a bill, the machine pushes the bill out and the customer must remove it from the slot it was placed in.
Paper currency detectors
Also known as bill validators or bill acceptors, paper currency detectors scan pliant currency using optical and magnetic sensors. Upon validation a series of pulses is generated using a multi-drop bus communications configuration which is then sent to the vending machine controller (VMC). Various interfaces exist for the VMC including a MDB2PC and MDB2USB.
Coin detectors
The basic principle for coin detection is to somehow test the physical properties of the coin against known composites from coinage that is acceptable. Some of the first designs usage of weight failed to stop people from creating slugs of cheaper metal that weighed close enough to real currency to fool the mechanics of detection. Nowadays it is common to use a laser and electrical current to test various characteristics of the inserted coin that has virtually eliminated the problem as any significant amounts of currency are in paper and electronic form.
Electronic currency detection
Adobe in its flagship Photoshop product from the CS version onward includes a currency detection algorithm in it that has been easily circumvented. Many hotels, cruise ships and arcades, especially in Japan have systems that use magnetically stripped cards to be charged up with credit that can exclusively be spent in their establishment.
See also
Sources
Currency Detector Easy to Defeat
"Currency detector"