Building a computer on a breadboard is a seminal project for many builders, but it can become complicated quite quickly, not to mention that all the parts needed for a computer are being placed on a medium which often lends itself to loose wires and other hardware bugs. [3DSage] has a working breadboard computer that is as simple as it can possibly be, putting it together piece by piece to show exactly what’s needed to get a computer which can count, access memory, and even perform basic mathematical operations.
The first step for any computer is to build a clock, and in this case it’s being provided by a 555 timer which is configured to provide an adjustable time standard and which steps through the clock pulses when a button is pressed. The next piece is a four-bit counter and a memory chip, which lets the computer read and write data. A set of DIP switches allows a user to write data to memory, and by using the last three bits of the data as opcodes, the computer can reset, halt, and jump to various points in a simple program.
Although these three chips make it possible to perform basic programming, [3DSage] takes this a bit further in his video by demonstrating some other simple programs, such as one which can play music or behave as an alarm clock. He also shows how to use a fourth chip in the form of a binary adder to perform some basic math, and then packages it all into a retro-styled computer kit. Of course you can take these principles and build them out as far as they will go, like this full 8-bit computer built on a breadboard or even this breadboard computer that hosts a 486.
This sounds a lot like a 4-bit machine I built with perf board and dead-bug wiring as a teenager in the ’70s. It used a lot more than 3 chips though, it was all TTL except for the, you guessed it, 555 timer used as a clock.
This would be more effective at computing if you added a ROM so that it executed microcode for each instruction.
Was thinking (nearly) the same – adding another EEPROM for storing only the opcodes/programs and thus separating opcodes from operands.
I think the whole point was simplicity, and combining opcodes with operands in one 8-bit word was to show that it can be done simply.
@03:38 7805 and NE555
@04:44 74161 Synchrounus 4 bit counter
@07:26 CDP1824 23*8 static RAM
I’d say it’s a bit much to call this a computer. It’s barely a state machine.
But it does trigger some memories from ages long gone by. Back then there were some pattern generator projects based on counters and Eprom chips. You could combine that with an ALU (or ALU logic) and even do 8×8 multiplication in a LUT. But still the principles are very similar to that used here.