How does coin recognition in vending machines work?

by | Mar 31, 2010 06:00 AM ET

You Asked:

How does coin recognition in vending machines work? --- Joey, San Dimas, Calif.

Marshall Brain Answers:



If you look at How Gumball Machines Work you can understand how the simplest possible vending machine recognizes coins. It uses the simplest possible coin detector. All that it looks at is the diameter of the coin.


Checking the diameter is pretty easy, as demonstrated in this video:

The machine can also expose the coin to a magnetic field and see what kind of signal it gives off as the coin rolls by. A steel coin will have a different magnetic signature than a silver coin would. A plastic coin will not respond to a magnetic field at all. This page has a nice diagram.

Bonus: How coins are made:

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