What is the right way to go talk to VC or patent attorney first?

From what you have told me I would say yes. Provisional patent applications are useful when you want to be able to lock down the starting date of your patent application without spending all of the expense of filing a utility patent until you know if you will be able to make any money from your invention.

Concerning inventions, whether you plan to speak to a VC or a potential customer or even your third cousin on your mother?s side, it is always best practice to get some sort of patent application on file prior to making any disclosure outside your company or a non-disclosure/secrecy agreement. Specifically with respect to VC's, disclosure to a VC is a publication of the invention like any other. So if you don?t have anything on file, you will trigger the US statute of limitations of one year could blow your international patent rights. Whether you should file a provisional or a non-provisional application before meeting with a VC is a question of resources and timing. Generally speaking, we strongly prefer non-provisional applications simply because you can only claim what is contained in a provisional when you convert it into a non-provisional, so if you are not careful and complete, you may miss something important. We reserve provisional filings for specific, strategic purposes only. With respect to the time and expense of obtaining a patent, one should always view that as an investment in the creation of value in and around your business enterprise. It is not cheap nor should it be. But it doesn't have to break the bank either. And the US Patent Office is getting more and more efficient. Bottom line get something on file before you speak with a VC.

Provisional patent applications are a common way to solve that dilemma. It shows the VC that you have some skin in the game and that you are protected. It also gets rid of the need for non-disclosure agreements, which are annoying to them.

Talk to a patent attorney first and file a provisional with assistance from the attorney - then go see the VC - for the reasons specified in the question. Beware of the one-year grace period of any public disclosure of your invention - especially since you have a prototype made. The provisional application must be complete under the patent laws - which is why you need help from the attorney. The provisional will expire in one year - but the invention will be "patent pending." Also, having the provisional on file may help you with the VC - as the invention will have some initial protection attached.