I have looked forward getting an Arduino board for quite a while now and I have finally come up with a thing I would love to try to make. As the topic title says - I'd like to make a money counter. I have thought about this and have come up with two ideas. First - to use a photo diode. I guess it would be easy to make a coin counter as you could just add one to the coin total when signal is interrupted between the photo diode and the light emitting diode. I am quite new to electronics, but what I remember from school and university classes this is how a photo diode works - current flows through it when there is light? The problem with this one is I have no idea how would I be able to get the size of a coin, so I could make correct calculations on the amount of money.
Second - using some sort of a mechanism where the coin has to be pushed through and the opening of the mechanism determines the value of the coin by it's size. The problem with this one is that I have no idea where to or how to make a mechanism of that sort.
I know that both approaches are quite easy to fool as they do not check whether the coin is real or not and so on.
Any comments and suggestions are more than welcome!