How do Dollar Bill Changers and Validators Work?
This is my site Written by The Vending Guy on January 10, 2008 – 7:01 pm

How do Vending Machine Dollar Bill Changers and Validators Work?
And Why do they Fail Sometimes?

If you have vending machines that use Dollar Bill Validators the most common complaint you will get is, “What doesn’t the machine take my bill?” Or you may hear, “Sometimes it takes my bill, sometimes it doesn’t.” Below is a crash course in how dollar bill validators work, and why they fail. I hope this information is helpful.

Dollar bill validators work using one of several techniques. The higher quality validators use multiple techniques to allow for wrinkled bills but still detect counterfeits. It also has to be able to determine if the bill is the correct denomination (meaning did you put in a $1, $5, or $10 bill).

Most bill validators have a sensor similar to the one found on an old tape cassette because US Currency uses magnetic ink on bills.

The second most common method for identifying the bill is using a photocell (similar in function to a tiny camera) and compares it to valid patterns stored in memory. Different patterns from different bills can determine the denomination.

Now that we know this lets look at why the bill “failed” in the first place. The wrinkled or crumpled bill had too many deep creases in it. Most likely the folds occurred at the spot the validator “looks” with the photocell. This makes the bill appear incorrect to the validator.

By folding the bill, or using some other type of “flattening method” you smooth out the wrinkles in the bill to allow it to pass the photo check. The better validators allow a certain number of failure points on the bill, cheaper ones allow only “crisp” bills to pass.


2 Responses »

  1. Hello, can you please post some more information on this topic? I would like to read more.

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