Al, I'd like to add one more bit of "correction" just to your description of this project. It is certainly totally usable as is, however, it is not a "true" trapezoidal accel/decel curve. To get trapezoidal curves you need fancy math that involves integrals, or some approximation of the integral that cuts it down to division.

Simply adding or subtracting a fixed time between each step does provide acceleration, but the curve comes out logarithmic. The shorter the time between steps (i.e. faster motor rpm), the faster the acceleration (steeper accel curve). This may not make a difference for many applications, but if you are trying to synchronize or optimize any motion, it is important to note.