Ok, I searched the archives and found nothing, but I gotta think this has been addressed before.
I’m trying to purchase a soda from the machine and it rejects my dollar. I examine this crisp, unmarked, untorn, unwrinkled bill, looking for that one defect that keeps the machine from processing the transaction and find none. I insert the damn thing four or five times over with no success, flipping the bill, rotating, nothing works. So I pull out another bill, also crisp, unmarked, untorn, unwrinkled and, except for the serial numbers, appears to be an exact duplicate of the bill I used before.
It goes through without a hitch.
What the hell are these machines detecting that prevents a seemingly normal bill from being recognized as real money?? Is it a wrinkle occuring after insertion? Or has someone installed AI in the machine capable of an “I want to f*** with you” attitude?
And if someone knows where this has been addressed before, please send the link. Thanks.
Well, this is just a WAG, but the dollar bill scanners used in American Post Offices and those Euro-converters you see international airports scan the bills both optically and using the magnetic signiture of the ink (which is why they you have to have 'Ol George facing the proper way when using them, but not always with a vending machine) and that they had problems with heat and light messing with the magnetic profile of the bills. Maybe it had somthing to do with that.
Well, it’s almost impossible to say for sure, since we can’t look at the bill and the scanner ourselves.
But we can guess based on what we do know. Soda and candy machines use optical scanners. Both bills were crisp and new, apparently identical.
What could have been different about them? You should examine the four corners of the front of the bills, looking at the complex scrollwork around the numeral “1.”
See how the color fibers in the paper are randomly distributed? It’s entirely possible that the specific arrangement of these fibers in the first bill interfere with the corner patterns that are used by the bill scanner to identify a real bill. If enough of these fibers arranged themselves just so, it might appear to alter the pattern in the corners enough to put the bill over the “reject” threshold. It’s a longshot, but it could happen. If this is the case, then your bill will not work in any machine that uses the same bill scanner.
You also want to look for variations in the printing process. Misprinted bills are supposed to be identified and destroyed, but some will inevitably get through. Even small errors that aren’t readily noticeable can interfere with bill scanners. ISTR reading how they are designed to reject common photocopies of bills, but I could have been reading about the more complex post office vending machines.
The identification of a bill is a statistical process. All kinds of screwy things can happen when you use statistics to make conclusions about an individual sample.
I’ve worked on these things, believe it or not. Virtually all dollar bill scanners are magnetic (I was working on one that was going to be optical, to try to exploit new technology). I suspect your problem was wrinkles in the bill or dirt. I’ve had this frustrating problem, too.
I’ve seen a few dollar bill scanner demos at optical engineering conferences, but so far as I know, no one is using them in Coke machines and the like yet. They’re harder to automate than magnetic scanners.
What can you do with a bill to make it more readable? Does straightening/flattening it do anything? Fixing corners? Are old bills harder to read than new ones?
I mean – I’ve always assumed that it just needed to be flat enough for the machine to get a good read and that was why new bills were better. Now I’m being told that it’s all magnetic, so what can I do to help a bill get through?
Here’s something I was once told. The bill scanners can be adjusted in some way that affects the range of bill quality they accept. Naturally, they’re usually adjusted to accept average-condition bills, so bills in very poor shape will be rejected. But bills in near-perfect condition may also be rejected. If the scanner is rejecting a new bill, try crumpling it up before retrying it.
Howstuffworks has an interesting column on this topic. I was particularily interested in the “Currency Testing System” link towards the bottom of the page.
I’d summarize it, but it’d take too long. Suffice it to say, the damn things examine everything.
*I apologize, but there is a pop-up that accompanies that link. Nada I can do about it.
“OPERATION: the bills are pulled in by a double belt driven by an electric motor. The bills are validated by the joint action of five light sources that detect the colour, the watermark density and reflection intensities. A further check is also made on the length of the bill, with a tolerance margin of 1.5mm”