How can I make each of my projects to have their own revision number?

The revision number is only relevant to the whole repository, and cannot be changed.

The global revision number attached to the repository is meaningless from a user's perspective. It's an internal mechanism that accomplishes the goal of the underlying schema design. It happens to be exposed so that the user interface is a little more convenient and doesn't require having to type very long date/time strings.

The revision number has no impact on any other factor of what you store in the repository. Repository revision number bumps aren't useful enough to be an accurate indication of the real rate of change of a given code base.