Building A Computer?

Building a computer these days conjures images stuffing of CPUs, memory modules, and hard drives into a motherboard and throwing the whole thing into a big black case and running Windows or Linux.

But how about really building a computer, with micro chips and a soldering iron?

In a recent SolderSmoke podcast OM N2CQR asked the audience if anybody had a spare CD4019 chip to replace a defective one in his frequency counter, so I searched through my junque box for the part, but alas no such luck. However, in the process I cataloged the ICs (so I can just look up parts in the future) and found quite a trove of IC chips including logic, memory, and several CPUs. A microcomputer or other microprocessor based device could be built with the parts on hand, I thought.

I remember fondly my days in high school when we had a H-89 to play and learn with and then later, learning about assembly language programming using 8080A "trainers" and decided it would be fun to recapture some of that magic. So here's what I have to work with:

• Several CPUs including Z80, 8080, and V20 chips.
• Z8 romless microcontroller
  
• 6kb worth of 2114 static RAM
• A 2764 EPROM
• assorted 74-series and CMOS chips
• several DAC08 D/A converters

The project guidelines are simple, whatever is built must:

• use mainly parts on-hand. A few inexpensive parts may be purchased if needed, but no big cash outlay is allowed.
• be useful. The unit must be capable of performing some useful work.
• look good. It should be housed in an attractive enclosure with neatly labeled controls.

Some possible projects include:

• A microcomputer, this is the obvious choice. Some very nice work has been done with homebuilt computers. The Magic-1 is a handmade microcomputer including homebrew CPU, not a microprocessor. Nice!
• A music synthesizer. The DAC08 chips could be used for waveform synthesis. The Z80 in particular, has been used in several synthesizers for control and sound generation.
• A weather data monitor and logger. A microprocessor based unit could sample wind speed, direction, air temperature and barometric pressure.

My inclination is toward using the Z80 as they are more sophisticated than the 8080A and I have two of them on hand. With only 6K of static RAM, the memory situation is a bit lean, but maybe I can pull the old DRAM chips from my PC XT. That's 640K, and Bill Gates said that should be all I need, or did he?