Your project may be free-as-in-speech, but that doesn’t mean it has to be free-as-in-beer. This handy coin validator/acceptor module is just like the ones you’ve seen in arcades. First, program it with what coin you want it to accept, any coin from 10.8mm to 25.1mm in diameter can be used so you can use American, European, Japanese, Canadian, etc. coins as long as they fit. When a valid coin is inserted, the output line will pulse for 20-60ms (configurable). The acceptor looks for diameter, thickness, dropping speed, etc to determine if a coin is valid. You can also select 3 different “strictness” levels.