pedram:
Hi,
Is there any way to earn money via Arduino?
Use Arduino to automate or assist some job.
Package that with a very small board or stand-alone chip for the controller, you program it with your Arduino.
If you use some public domain libraries like SD, you are required to keep your software open. But write your own and you can keep your secrets, AVR chips can be locked from practical means of reading the code.
But first, try making things not to be sales products just to learn do and don't of making. Find out what you can do before wasting time dreaming too much. Get up with your code, poor coding limits what can be done more than 99%.
What you can do when adding parts to the controller is enormous. Dozens of sensors and motors are not too much, IR remote is not too much, SD cards are not too much, switching house mains is not too much, even having it call your phone or send web data to a site is not too much... but it all comes at some cost and ability to wire up and code and invent which is up to you. Don't spend big until you can do more than small.