I'm a TA for an undergraduate signals and systems class. As part of my job, I need to prepare some homework problems. My co-instructors use Microsoft PowerPoint to make the diagrams, but I find it very difficult to use, since we need to copy/paste objects and carefully place them in precise spots. I'd rather write code. Is there some LaTeX package specifically for this purpose? Or, is there an alternate way to draw these diagrams? How do instructors typically do it?