Global Class Method

I've written a sketch in Arduino 1.6.5, in the sketch I have made a class in the .pde file

What I want to do is instantiate an object in setup (not sure how to format code for this forum)

void setup()
{

MY_CLASS my_class_instance();
}

What I want is to use that class instance in a function called by a timer.

void calledByDUETimer(){
my_class_instance.some_method();
...
}

But I get a complaint about it being out of scope.

Can I have "global" instance of that class?

Or, can I pass in a reference to that instance?

How to do this?

My C++ coding is not advanced to making header files, but I am not sure that would help.``

What I want to do is instantiate an object in setup

Why? Making it global makes far more sense.

Can I have "global" instance of that class?

Of course you can.

Or, can I pass in a reference to that instance?

Pass it in where?

How to do this?

MY_CLASS my_class_instance();
void setup()
{

}

Of course, MY_CLASS is a dumb name for a class.

Just move variable declaration out of setup() function to make it global?