Dollar bill changer

A bill changer is a dedicated vending machine that accepts bank notes and dispenses coins. In some cases the machine subtracts a small amount (e.g. 5 cents) as a surcharge for the transaction. This is particularly common where the merchant expects the coins to be used on the spot in other vending machines. Electronic bill changers can be found next to other vending machines, especially those that lack bill validators. The Antares vending machines usually have a bill changer mounted on the side.

A bill changer next to Antares vending machines has to work with all sorts of bills, from crisp new ones to ragged old ones. The device can tell the real bills from the fake ones. In many cases the changer must also be able to sense the denomination of the bill. In order to accomplish these tasks, dollar bill changers use a variety of technologies. Below are some techniques that people have employed. Some of these techniques have changed over the years as microprocessors have allowed more capability in the device.

Here are some of the techniques that have been tried:

1. Many of the early bill changers took advantage of the fact that U.S. bills are printed with magnetic ink. They would use magnetic heads (like the ones in a cassette tape recorder) to pick up signals from the bills. Areas of the bill would generate signals at a specific frequency, and the detection of this frequency would validate the bill. Different bills generate different frequencies, so the frequency can also determine what the denomination is.

2. Genuine dollar bills have certain conductivity, and checking for the resistance of a bill can authenticate it.

3. Inks and papers have different fluorescent properties, and these properties can help to tell the difference between real and counterfeit bills. No one should try to insert a fake dollar bill in Antares vending machines, it will simply not work.

4. The optical properties of a bill, or a strip of a bill, can be sensed with a photocell or a camera. They can then be compared to valid patterns stored in memory. Different patterns from different bills can determine the denomination.

A good bill changer like those found in Antares vending machines use several of these techniques because people seem to have a strong desire to outwit bill changers. These techniques that are used in bill changers such as the ones placed next to Antares vending machines, are foolproof and it will be next to impossible to outwit them.