Instructables

does anyone know how a bill validator(aka the thing that takes your dollar in a vending machine) work?

i've been wanting to make a vending machine, and i have built a quarter mechanism , yet i want to have a mechnasim to take dollar bills. the easiest way to do this is to take a existing bill validator  and hook it up to a micro controller. yet to do this i need to know how it works. is the the system self contained (if i plugged it in to a power source would it work) or would i have to hook it up to a main controll system.

RedMeanie4 years ago
To answer your question....Yes you would need to use a self contained unit. They can be found all over at vending machine repair shops. Im sure there are a few in your area if you live in the US. They generally send out an electrical encoded pulse that run to a circuit board. At least that is how our coke machine worked.
mrbones121 (author)  RedMeanie4 years ago
so in other words if you take the dollar bill scanner and plug it into a power source it will accept or deny a dollar bill
Yes the older ones will. Im not sure about the newer multi-denomination acceptors though. I would imagine they are self contained also, but that is a guess. The bill acceptors are made by different people than the vending machines so it would seem rational that they would make the units as independent as possible.
mrbones121 (author)  RedMeanie4 years ago
So does ur coke machine bill scanner plug into a main "computer" system
Yes but it is just the relay controller board. I believe it just "Validates" payment and triggers the relay system board basically accepting that full payment has been made. It also is connected to the coin reader so Im pretty sure thats what it was.
I dont have the machine anymore or I would send you pics and try to make a better description. Im trying to give you the best picture I can based off of memory.
What I would do is just ask a vending person. Im sure they will enlighten you. All you need to do is go to a set of machines and look on them for te company that services them. They will be in your area for sure. Then call and ask if you can come by and talk to them. If you tell them what you are working on Im almost certain they will help and give you some insite. They may even give you some old stuff to work with. Worth a shot right?
If it was designed as a standalone unit, yes.

If it was integrated into the rest of the machine's electronics, the same processor may be doing the scan validation and triggering the dispensing relays.

Depends on the exact model.
Burf4 years ago
Obviously, vending machine manufacturers would rather keep it a secret but generally there are several methods.
Unique properties are encoded in the different denominations of each bill.

Detectors analyze the magnetic ink used in bills of different denominations.
Digital scanners read hundreds of reference points on the bill and compare them to data stored in memory.
They can measure the electrical conductivity of the bills.
Ultra violet scanners read the values of fluorescent ink used on the bills.
Probably others that aren't know to the general public.

The readers can scan for some or all of these, depending upon the sophistication of the reader.



Burf Burf4 years ago
I should have mentioned the U.S. Mint encodes numerous anti-counterfeiting features into the bills and some of them are highly secret.
And others aren't. If you hit the Mint's website, they have pages describing the new bills which point out the more obvious changes (the watermarks, embedded security threads, microprint and so on.)

Which characteristics any given validator looks for are definitely proprietary information. So, yes, they're self-contained units which just report whether a valid bill has been inserted and which denomination if so.
frollard Burf4 years ago
To add to the pile: checking and validating the serial number on the bill (out of range, same number used consecutively, etc)
kelseymh4 years ago
You buy it as a self-contained unit, preprogrammed for a particular currency set. Since, as Burf pointed out, some of the validation features are classified, vendors cannot release the details of their validation schemes.

In order to find actual devices, my Google search was "buy U.S. currency validation reader".
yokozuna4 years ago
It rejects your dollar 30-40 times until it figures that any counterfeiters have given up and finally accepts the dollar as you race to avoid death by dehydration.
aeray yokozuna4 years ago
+1