On Wed, 27 Nov 1996 09:01:50 GMT+2, Werner Terreblanche wrote:

>>>I need to build a controller for a coin operated machine, which has
>I once opened one such mechanism that come from a one arm bandit slot
>machine.   It works on a metal detector principle with two separate,
>but similiar search coils.

I also have opened several coin operated mechanisms.
The simplest ones just roll the coin down a sloping plane in such a way
that only a coin with proper weight and size will trigger a microswitch.

A more advanced mechanism I found in a coin operated telephone.
In it, the coin is rolled down a sloping plane. In the track there are
two stations. One that capacitively senses the size of the coin, by
an array of electrodes on a printed circuit board, and
another where it passes by a coil, where I guess it inductively senses
the material of the coin.

My idea for making a coin validator myself (with a PIC of course), was
to sense the size with an array of LED-Photo diodes, and the material
with some kind of inductive sensor. If the coin has to roll down a sloping
plane with a certain speed, that can be timed by the pulse length from
the photodiodes/capactivie sensors, any interference with the coin, like
attaching a string to it, or something, will give the wrong result.
You can also put a special sensor, so that if the coin is pulled
backwards, the validator will enter some kind of tilt state.