Okay, this has happened to me twice this week now. Over the weekend I was trying to buy stamps from the vending machine at the post office. I had a wallet full of nice clean crisp $1 bills, and the vending machine didn’t want to take any of them. I spent probably five minutes feeding various bills into the machine and having them spit back out at me. I made sure none of the corners were bent, bills were flat, had them facing the direction the bill accepter indicated, etc. No dice. Then for some reason I decided to try feeding the bills facing the wrong direction, and the machine just snapped them up!
This morning I was trying to get some coffee out of a vending machine at work, and the same damn thing happened. (Yeah, I know, vendo-coffee… what can I say? I was desperate.) After the first couple attempts at feeding a dollar bill, a little voice in my head said “Remember the post office!” so I turned the bill around and voila – in it went!
So why doesn’t a vending machine bill accepter accept the bills facing the “correct” direction, but accepts them facing the opposite direction? Are bill accepters generally designed to accept bills facing either way, or do they just have something installed backwards? (Another interesting side note is that in both of these cases, the machine continued to malfunction after it took my money. The stamp machine did not want to give me the correct number of stamps, and the coffee machine forgot to drop a cup before it started pouring.)
There are 4 orientations available for any given note, in general bill acceptors should be able to handle any of the four (very cheap bill acceptors may specify an orientation).That said a few background notes about how acceptors generally work will help explain the problems you are seeing.
Due to the nature of the beast bill acceptors have to be able to split things into categories, not a valid note, $1, $5 and so forth based on being presented with a wide range of note qualities. To cope with this an algorithm is designed that will take the input from various measurements and decide which if any note has been presented. Factors typically include size, translucency at various points, colour and so on. These algorithms cannot however be created as a purely intellectual exercise, what instead happens is that at some point it is somebody’s job to take a whole bunch of notes and pass them through the sensors in order to ‘train’ the algorithm. It is during this process that many problems occur, if the note set presented is not large enough to provide a good range of notes you can get interesting problems of the type that you describe. Perfectly good notes are often rejected precisely because they are unrepresentative of the average note in the field or because the algorithm involved is more lenient on one face than the other.
As an example of this after the introduction of the euro notes in 2002 there were two firmware updates made available, one a few days prior to the changeover and one about a month later once someone actually owned some grubby euro notes (the first dataset being based purely on pristine notes)
I dunno, but I had the same problem in DC yesterday trying to buy a Metrorail pass… I had $8 in singles and the machines wouldn’t take any of them. I had to beg some guy to “swap” 2 of them with me!
Sounds to me like the bill reader was backwards on the machine you were using (or maybe more likely, the sticker was). But as a data point, there are definitely newer machines which will accept the bills either end first (face-up only, though), yet they still have a picture showing you which way the bill is supposed to go in. I’ve always assumed that this is because even if the bill can go in either way, people are more confused if there aren’t instructions, and a picture that means “put it in this way” is more obvious than trying to explain that it can go in either way.
So to make a long story short, your machine could have had the reader installed backwards, or it could be one of those ones that accepts bills either way, but is damaged.
This last point is correct, people like clear instructions.
Of the 10 or so different varieties of bill acceptors I’ve worked with or evaluated, not one of them was symmetrical in a manner that would be conducive to being installed backwards and working in that state. Most have a very obvious front and back, one with a note acceptance opening and one with an interface to the note stacker. For example see here. It’s not out of the question that the machine is damaged, but I’d bet rather heavily it isn’t in backwards
makes me pretty glad I’m in canada, with no one dollar bills anymore… or two dollar bills. (We have them in coins now, the loonie and the polar bear respectively.)
