If you think it's already been done and it might serve no purpose, then you haven't lost any worthwhile motivation. You could continue with that project when and if you feel like it, a little at a time. It's good to have little, unimportant projects like that. They allow you to be moody and still always have a project that fits your mood. It helps if they're not all programming projects, and you could include hobbies and sports as "projects".
Interest is sparked by a good idea, and sometimes by other things, but it's not not easy. Trying to spark interest in a particular field is very limiting and harder. Sparking interest in a project that's probably useless is the hardest of all.