One thing about my “Introduction to Digital Computers” series I wanted to verify was that all the circuits designed in the series in fact works correctly.
And one aspect of that–which we introduced in the first part of the fourth video–was the complete ALU.
While I’ve taken the liberty to do some minor redesigns (so as to reduce the number of transistors–things like realizing we don’t need a separate XOR circuit if we already have A XOR B embedded in the adder circuit)–I’ve built a circuit that is entirely made of transistors and resistors (with a couple of status LEDs to show the outputs visually on the board) that actually is a full 1 bit slice of my 8-bit ALU.
And I’m unreasonably happy that it (the second iteration of the circuit board design) works flawlessly.
Of course I have 7 more blank boards and a whole bunch of resistors and transistors on order.
And when they arrive I plan to wire it all up to demonstrate that the principles introduced here in fact work as advertised.