You may want to find out if the code sample will be part of the interview, or merely part of a screening process. At least that way you may put together code that you would like to discuss versus code that would impress others when they review your code.

Also, maybe there's a portion of your homegrown project that is ready for prime time and easily discussed in an interview setting. If that's the case, then you could discuss the library and how it supports your current project.