Hi,
I am an electronics and computer engineer, I have a specific experience on what you're looking to build and have built something similar before.
I am going to keep this short, and we can discuss further over chat or over the phone if you are interested.
I have few questions, are you looking for compatibility accross various levels of vending machine or you have one type in mind?
Let me know if you are interested.
Best regards,
Nabil