How do vending machines and other money counters (especially older models) differentiate between what coins/bills are put in?
In: Economics
The oldest ones that only accepted coins used the size of the coin to sort them. The ones that accept bills use a camara
Coins are easy, all you need is a couple grooves in an angled surface. As the coin slides down, it falls through the larger grooves until it hits the correct size, at which point it can’t fall any further. Instead, it slides along the groove until it reaches the container for that kind of coin.
Amusement technician here,
Modern machines use an electronic comparitor that reads metallurgical content the coin as it runs through the first part of the mechanism. Then seperates the good from bad in the next half. Then informs the machine it has a good coin.
On insertion the coin rolls down a ramp past some electromagnetic sensors as well as optical sensors. In the first half it reads the approximate size and density of the metal and compares it to profiles that are pre-programmed into the mechanism memory.
If the coin is a dud or doesn’t match ones currently set to be accepted, the coin simply makes a turn processes through the second half, and rolls back out into the reject slot or chute to be returned to the user. (This “do nothing” approach is so if the machine has no power, coins will automatically, without power or intervention, be returned to the user)
If the coin is good there is a gate that is electrically activated. This opens the bottom of the acceptor. This opening allows that coin to be blooped into the coin acceptor box before it has a chance to roll through to the reject path and be returned.
Now that the coin has been accepted, the last thing that will happen is it breaks an optical beam that verifies the coin has fallen into the coin box. This keeps people from “stringing” coins to get them back, as the string, fishing line, tape, whatever, continues to interrupt the optical beam. Once the beam has been broken…the gate closes, and once the beam is clear again, the final part can happen.
There will be some wires connected to whatever device it is attached to, some of them will Inform the device with a pulse that a “credit” of a value is due. Typically each type of coin will have its own wire…but some can be programmed to pulse multiple times to indicate which kind of coin is inserted. (Ex. If the machine only accepted 2 dollars to activate it could do what’s called “accumulation” and once you’ve inserted 8 quarters or 20 dimes or 40 nickles (or any combination thereof, it would activate it’s pulse one time. Conversely, if it accepted only quarters and you inserted a dollar coin, it would pulse the output 4 times)
Alternatively there are some cheaper single coin acceptors, where you actually insert in the mechanism, the type of coin you wish to be accepted. This sizes the slot and provides a metal sample to compare to. All others either get stuck and have a button to clear the jam out, or simply roll through.
Older machines like washing machines and pool tables that have a slide mechanism rely solely on the coin being a certain size. If something of an appropriate size is inserted into the slot, and the slide activated to push the coins in, the coins will push down a hook that keeps the slide from being pushed in all the way…since this hook is being pushed out of the way by the coins, it goes all the way in and activates a mechanical mechanism to open a gate or push a lever or button to activate the machine or release pool balls or what have you.
While still others have a gated acceptor that has levers and weights that when a coin of appropriate weight and size is inserted, will properly tip the weighted levers correctly, and will also pass by magnetic restrictors that will properly slow (or not slow depending on the coin) fake steel slugs or washers.
Modern bill acceptors work very similar to the modern electronic coin acceptors. The bill is scanned with optics (using certain visible colors, infrared, and ultraviolet light) and sensors 100’s of times across its width and down its length as it’s fed into the acceptor. The time it takes to feed through and break/clear the optics let’s it know if it is the proper length. First if it’s not a proper size, it’s immediately spit back out. If the size is good, The optical values are compared to values stored in the acceptor for known good bill scans. If it matches within a certain percentage (selectable by the operator.) It is deemed good.
It will be then fed into a box for storage. Once the acceptor has verified the billpath is clear (ie keep people from attaching strings or tape to the bill in an attempt to retrieve the bill) it will be placed in the box and “stacked” with the others. The billpath will be checked again to be sure it’s still clear. Only then will the “credit” be issued to the system. Similarly to the coin acceptor, pulses are used to inform the machine what’s been inserted.
For anyone thinking THEY are smart enough and could use a string to retrieve their money, good luck. the acceptors are setup as a one way trip for accepted money. There are spring loaded fingers and flaps that only allow things to pass through one way, and often, cutters or other sharp spikes at key points to cut strings and tape from being able to pull stuff back through. I have found tape and string attached to money before. Nobody has been able to retrieve it. These systems have been able to thwart it
Obviously not all machines work the same. But some coin machines operate based on weight. I worked at a carwash for my first job, and setting the coin box up was quite easy. You basically opened it up, press a button and put through 5-7 different coins of the same value. You use different coins so it gets an average weight. We had it set up for $1 and $2 coins (I’m Canadian) as well as two different tokens that gave the same time as $1 and $2 coins. Tokens got used for internal use as well as for people who paid for carwashes with a credit card.
In this case, each coin is assigned a time. Like quarters would be 30 seconds, and dollar coins would be two minutes. It was so possible to make quarters give more time than loonies. Other machines would assign a value to each coin (like 25 cents for a quarter) instead of a time like I did in the car wash.
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