Turning the Compukit 1 into a Computer

A project log for Limrose Compukit 1

Recreation of the Limrose Compukit 1 from 1970.

deftcoyotedeftcoyote 02/14/2021 at 23:230 Comments

A couple of places have noted that the Compukit 1 could qualify as one of the earliest home computing devices available to the public. This definitely depends on what you count as a computer. I've been playing in logism with the gates and have come up with a legitimate computer that can be made using the Compukit 1. My design shows 4 LEDs, but you can ignore the 2nd two if wanted. It only requires adding 4 switches (or buttons). The logism diagram is below. The gates are labeled the same as on the Compukit.

Computer description: 1-bit Accumulator A(via SR flip-flop), 1-bit memory M(via gated SR flip-flop), 1-bit ALU that implements a NAND between A and M. Since NAND is universal, all computable functions can be implemented (with more memory).

The input:
  Button 1: Set A to 1, A=1
  Button 2: Set A to 0, A=0
  Button 3: Store value of A in M, M = A
  Button 4: Set A equal to the NAND of A and M. A = NAND(A, M)

  LED 1: 0/1 status of accumulator A
  LED 2: 0/1 status of Memory M
  LED 3: Power (optional)
  LED 4: NAND(A, M) (optional)

The purple lines set A to the output of the ALU, but due to the way the buttons work, it messes up the simulation, however, I don't think this will be an issue in the real hardware. Also, to start, it's necessary to turn the power on, which holds the NAND line with a positive input, then set A and M just to get initial values on the lines. If anyone has any thoughts, I'd appreciate it.

There is one gate not used, and I included 2 additional gates in case I wanted to use the deluxe model of the Compukit 1 instead, which had 16 rather than 14 gates.

In relation to the hardware, I had a prototype board printed after widening the tracks to .6 (instead of .25 that's in the uploaded kicad files). Unfortunately, they routed the tracks as if they were meant to be on top (so the board is mirrored), but another one has been printed and I'll pick it up this week. Here's a picture of the mirrored one.