How to Build a 4-Bit Computer on Breadboards Using Individual Transistors

A simple 4-bit computer is built on breadboards using individual transistors. This computer is called the GSN477. This is because it was built for the Global Science Network, is 4-bit, and contains two 7-stage counters.

Sections of the computer are the clock, program counter, ring counter, 10 bytes of memory, opcode register, opcode decoder, control matrix, data bus, accumulator register, output register, register B, and ALU.

Circuits are built using NAND digital logic gates, XOR gates, AND gates, inverters, buffers, and tri-state buffers. Larger circuits include D flip Flops, MS D flip flops, Edge triggered JK flip flops, and MS JK flip flops.

The computer shows how computers add and subtract numbers while running a simple program and this video was submitted for the #some3 competition.

0:00 Intro.
0:51 Computer overview.
1:30 Example program.
4:12 The clock
4:22 Ring Counter
4:53 Program Counter
5:33 10 Bytes of Memory
7:01 Opcode Register
7:11 Opcode Decoder
8:19 Control Matrix
9:06 Data Bus
9:44 Accumulator Register
10:21 B Register
10:51 ALU
11:15 Output Register
11:35 Building Suggestions

References:
Walker, J. S. Computer Time Travel: Building a Computer Processor from Discrete Transistors: A Look Back over 50 Years to the Beginning of Modern Computer Technology.

Oldfangled Publishing, 2017. Malvino, Albert P. Digital Computer Electronics. 1993.