These type of mini computers seem to be everywhere, many folks have built some version using transistors, TTL chips or whatever and while impressive they went to the trouble to do it, never seem to make them do interesting or useful things.
I have been building these since the mid 70s(that was pretty much all there was then) and love working with the nearly forgotten 7400 series parts. I have built them using led displays, 7 segment displays and VFDs. People probably think I am overdoing it a bit making so many versions of these but for me it is a fun and pleasurable experience. No two are ever close to being alike, although they may share many of the same parts. This version is a hybrid and uses both TTl and transistors.
One thing I decided for this version was to make it not only a fun experience to make, and have some educational experience attached to it was to make it do some really useful things. Nowadays just about anyone can code an Arduino to run a servo or stepper and shields make this task even stupidly simple. What gets lost for most is how things really work and what is happening to make servos move and steppers step.
This little 4 bitter will take you inside the magic and allow every step of the way to be probed and prodded, measured and visualized. Since there is zero code involved, the focus is brought to the hardware itself and for some this can be a new experience.
This project will attempt to untangle some mysteries and put forth a nice little machine to experiment with.
I use these extensively for test mechanical mechanisms like joints and 3D printed gearboxes as you can just plug them into a port and they can be selected to run. By tapping a few buttons thing go into motion so you can study them make modifications and even"life " test mechanisms by having them cycle on and off for as long as you like....no programming needed.