No contract or anything just tell me how to do it
I'm not a bad person
I tend to be of the view that a source release is not a source release unless the user has all of the bits and pieces to completely replicate the object code. So I see no point in discussing the various ways to obfuscate code that ultimately would never work with somebody determined to break the obfuscation.
If you don't want people looking at your code and possibly modifying it, don't release the source. However as I pointed out, if you used components directly in your code that are GPL licensed (not libraries that are provided by a distributor like arduino.cc), you are obligated to make the source code available in such a form that people can modify it and pass along their modifications.