I'm interested in finding out how a coin operated newspaper rack
operates. In particular, how does the machine "know" when the correct
amount is inserted?

I'm talking about the mechanical type of machine (no electricity, no
computers). Lets say the paper costs 50 cents. I can insert 2
quarters, 5 dimes, 10 nickles, or any combination of those coins
totalling 50 cents, i.e. one quarter, two dimes and one nickle.
Another combination that would work would be one quarter and three
dimes (55 cents). No change is usually given, but the machine "knows"
that at least 50 cents has been deposited.

It can't be based on weight as the different coin combo's would have
different weight values (5 dimes vs 10 nickles). I'm assuming it is
some sort of lever/trap system where; depositing coins will cause a
mechanism to move and line up with the lock mechanism (similar to a
typical combination lock).

A correct answer would have a detailed description of how the system
operates. Pictures of the operation/mechanism would be fantastic, but
are not needed if the explanation is detailed enough for my feeble
brain.

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Clarification of Question by cvenom-ga on 20 Jan 2006 06:09 PST

I kind of get a grasp on what you're describing, but think I'd have a
better idea with a picture of the actual mechanism.

If you can find a diagram that would be great. If not, you can post
your comment as an answer.

The simplest way to explain it is to understand that the coin
mechanism counts the coins total by counting which of 3 trip wires are
triggered. Being gravity fed, the coins slip through different holes
based on thickness of the coin, and trip a small "L" shaped wire on
the way to the coin box. This wire breaks their fall for a fraction of
a second and the coin is "counted." Dimes go first, being thinnest, to
the smallest hole, nickels and quarters pass this hole, next to fall
are the nickels, finally only quarters remain to fall and trip the
last wire. The wire is tripped just before you hear the coin fall onto
other coins in the cashbox. The mechanism is set to count up to $X, in
any combination to match or exceed before the final spring is tripped
to open.

Does that make sense?

You can see pictures here: 

http://www.kjack.com/home.htm