Dear Bravnot,
Pretty much every invention involves a combination of things that are known. Sometimes the combination is obvious, sometimes it is not.
For example, let's say the cassette Walkman exists and CD players exist. Replacing the cassette player with a CD player would seem to me an obvious combination and I think it would have been difficult to get a claim allowed that would say "a walkman where the cassette mechanism is replaced by a CD player."
Furthermore, even if it was non-obvious, you cannot have an idea like "gee wouldn't it be nice if I could CDs on my walkman" and then get a patent on the combination without providing a detailed technical solution. That's what you get a patent on: not on the idea, but on the technical solution to the idea. The broader you can claim the technical solutions, the closer you come to having a patent on the idea, but ideas alone can never be patented.
Getting back to the example, if you can't get a patent on the simple combination of a CD and a walkman, don't give up.
Ask yourself "What technical problems arise from this?" "Is there some problem that is not so obvious, but that everyone who wants build CD Walkmans will have to confront?"
Well, putting a CD player into a Walkman presents a lot of obvious problems to which the solutions are maybe not so obvious: vibration, battery efficiency, size, etc.
You would have to include circuitry to compensate for vibration. CD's use a Reed-Solomon coding that is pretty good against short shocks, but is crummy against longer shocks, or sustained vibration. Now I am not a coding expert, but I imagine there were many clever solutions to this which were patented.
Similarly, you'd have to design a special laser pickup that would work in the same vibrational environment. I bet there are non-obvious solutions here as well that were patented (or could have been patented.)
What you do is work from the top down looking for technical bottlenecks - those aspects of the design that everyone must pass through - and patent these if you can. You can sometimes even create bottlenecks by clever product design - a la Gillette, Lexmark printer cartridges, etc.
So the moral of the story is maybe you can't patent a walkman with a CD, but you might be able to patent a circuit without which no one can build a walkman and a CD.
And this is what patent engineering is all about - finding those inventions which may not be obvious the inventor.
Regards,
eric stasik