I want to make a raspberry pi arcade cabinet but I don't know how you would have it to only allow the user to place their game of choice when they have paid, and to let them play more than once if they pay more than necessary
I want to make a raspberry pi arcade cabinet but I don't know how you would have it to only allow the user to place their game of choice when they have paid, and to let them play more than once if they pay more than necessary
I can confirm what peteroakes says. I've laid my hands on a genuine mechanical coin validator, and that's a very complex apparatus. It even evolves validating drop down velocity of the coins.
The unit I reviewed didn't use any electrical properties to validate the coins. It was all based on size, weight, and how it behaved in the drop down path.
I've done a short blog on the subject of drink dispensers:
Repairing a Vendo V-80 cola dispencer of the 1950s
And here are some videos that I made on bypassing a defect coin detection system 
and on fixing a soft drink dispenser:
I used video recorder internals to detect that something went through the coin path.
I can't say that my story has a happy ending. I did this modification for a friend who had bought this cola dispenser for his partner. They separated not long after.
