Say that I own a business from around the 12th-15th century. My country uses a Silver (or, if you so wish, Gold) currency in the form of coins. I want to make a secure "vending machine" to give out objects in exchange for a certain number of these coins.

Here are the specifics:

  • The objects can be of any shape, size, or weight

  • The machine should preferably work with multiple coins, but one would be okay

  • The machine should be able to determine whether or not the coin is the right coin, which has a standard weight and size. It should be secure against most types of fakes.

My question is: Is this possible, and if so, how would it work?

  • I suppose the profitable ones are manned... – user6760 Dec 9 at 5:04
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    ANY shape, size and weight? Well then...a trebuchet vending machine it is. – James Dec 9 at 8:23
  • 15th century maybe, in a city with a particularly well-developed economy. 12th century no way; there were simply not enough coins in circulation to make the proposal worthwhile. As for shape -- have you ever seen pre-Renaissance coins? While they did have uniform weight, their shape was considered quite unimportant. – AlexP Dec 9 at 9:39
up vote 39 down vote accepted

Vending machines are actually quite ancient. Heron of Alexandria invented them a couple thousand years ago. Tobacco dispensing machines came about in the 1600s. Put a coin in the slot, the machine opens a valve and dispenses a product.

End of story, really.

There is no mathematical or engineering or fabrication reason why your medieval-esque society could not do something similar.

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The only issue I foresee is in counterfeit detection. In medieval times, I think counterfeit detection by weight will be your only viable alternative, if magic or a money changer is not available. If they have magnets of some kind, then they could be added to weed out iron slugs at least.

If the coin is determined to be too heavy or too light (and thereby either actually fake or else clipped (a common practice in the days of precious metal money)), then it would be dumped into a return slot. A coin (or slug) of correct weight and dimensions will be accepted. Whether real or fake!

A fairly foolproof system. Faking coins is, of course, big business and back in the day carried a hefty penalty for those caught doing it. A relatively simple detector will keep all but the most advanced counterfeiters from using the machine.

A final note: unless your vending machine is dispensing title deeds to large plots of land or luxury waggons, chances are gold coins will never see the inside of one. Probably not silver either. Most likely copper or brass will be used to buy relatively inexpensive items or services.

  • 10
    This. You have four controls in a simple system. (A) Slot width. (B) and (C) Two holes in the rail (the first—which it should not fall though—sets minimum radius and the second—which it should fall through—sets the maximum). (D) One or two roll-through balance(s) sets a weight range. The result measures geometry (A-C) and mass (so effectively density) and give you a reasonable ability to reject slugs. – dmckee Dec 9 at 0:33
  • you will actually run into the problem of the non-standard size of the legal coins, coins were often only roughly the same size and shape. often they were only vaguely round, the tamp was round but not the entire coin. A coin did not have a standard value the weight of the coin determined its value. – John Dec 9 at 12:32
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    @John is right. Pre-Renaissance coins do not have uniform shapes; it just wasn't a design goal. Uniform weight, yes, it's important. Uniform shape? Why? We don't have vending machines, so we don't care. – AlexP Dec 9 at 13:27
  • Necessity is the mother of invention. A vending machine that dispenses something needed by everyone, be it holy water or flour, will cause people to gripe about legitimate coins not working. Someone will eventually devise the relatively simple method of making coins reasonably uniform in shape as well as weight. – elemtilas Dec 9 at 18:53
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    @elemtilas No they will say this piece of junk doesn't work and if you are lucky never use it again, if you are unlucky they will break it trying to get their money back. – John Dec 9 at 22:09

Clearly quite intricate mechanisms are possible with sufficient understanding.

Karakuri Japanese Clockwork

As has been pointed out by @elemtilas, large gold and silver coins are unlikely to be used for the sort of items that would be dispensed by a vending machine.

If you insist on gold and silver then the machines would have to accept very small coins (tricky even by modern standards) or ...

Employ trusted peasants to sit inside the 'machine' and do the transaction whilst hidden from view.

  • - though a little later in time than in the question. Trusted peasants. – BentNielsen Dec 9 at 13:07
  • Basically an Automat! (The Automat was a fresh food vending system that required human workers behind the scenes.) Probably not a good fit for the 1100s, though. – elemtilas Dec 9 at 18:56

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