NOTE: The schematics incorrectly show the NPN transistors in reverse, with collector / emitter swapped.

This is my first attempt at doing a semi-serious project using digital logic. To really gain a good appreciation for the technology involved, i designed and built the circuit entirely out of discrete transistors instead of using pre-made IC's with logic gates (such as 74-series chips).

This adder is built entirely out of 2N3904 NPN transistors, 220k resistors for inputs, and 47k resistors for output pull-ups. There are a total of 152 transistors and 224 resistors, not including the LED resistors on the manual switch board. The first board in the stack uses an LM7805 and 10 uF capacitor to provide voltage regulation.

Because of the presence of a carry output bit on the 8th stage, this can technically output a 9 bit number. The A and B inputs are a single byte (8-bit value), so their maximum is 255, and the output can compute up to 510.

In the future I'm going to add a lot more features to this machine, like multiple RAM addresses than I can read/write to, a clock + ripple counter to increment the input bits automatically, and maybe even a binary-BCD converter which I could then use as an input to a 7-figure number display, which would give this computer a graphic output. I also want to add a reader for a 3d-printed punch card that will provide program instructions or data.

Music:
Kevin MacLeod - Groove Groove
Heatley Bros. - Dimension Drift
Prod Riddiman - Lost Time
Kevin MacLeod - George Street Shuffle

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