It's remarkable the difference that ~20 years can make. In middle school, someone's science fair project was building an actual briefcase bomb (with clay). It had a variety of sensors, and laid out (on a tri-fold poster board, of course) the guts of how each one worked.
And even pre-9/11 I'm still not sure what the legal status of that is. Since it was designed to be a "bomb," even if it is inert, several laws do cover that.
Essentially as soon as you describe a pile of distinct legal parts as a "bomb" you've now got a class of controlled weapon even if it has no explosive components.