Home Made Computer

The component parts of Bill's Z80 Home Made Computer design.

Commenting on the photo, Bill notes "the photo shows the somewhat sad remains of my previous attempt at a home made Z80 computer 20+ years ago. What got built did work, but I never got around to doing much firmware for it, I then got too ambitious. I wanted to add a bitmapped graphics display with glitch free updating. But however many designs I considered, with the components available to me at the time I invariably ran out of nanoseconds in propagation delay. "

The keyboard is a matrix keyboard of similar design to the Memotech MTX keyboard. There is almost no circuitry inside the keyboard unit, the majority of the electronics were external - see below.

The main PCB, containing the CPU, ROM, RAM, clock crystal and supporting components.

This contains the interfaces for the LCD display and matrix keyboard

The PCBs are fitted with DIN 41612 connectors with mating connectors fitted to a short length of ribbon cable as shown.

NAVTEX Decoder

Quoting from Wikipeda, "NAVTEX (Navigational Telex) is a service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships".

Bill's NAVTEX is a minimal Z80 based microcontroller.

There are three stacked PCBs, held together by threaded studding. The top PCB has the Z80, two static RAM chips, EPROM, and memory decode logic.

The short length of ribbon cable, with three plugs, running down the left hand side of the boards connects them in a similar way as Bill's HBC.

You can also see the LCD on the front panel (top of photo) and four buttons for user input.

The PDF contains a copy of Bill's schematics for the processor  design, as well as the RF circuits (which are included for general interest, even though they are not applicable to Z80 computers).

"A base view showing the dicast box containing the radio frequency stuff, and the power smoothing and regulation circuits.

My Memotech played an important role in the development of this unit. By far the most difficult aspect of the development was the radio frequency part. During much of the work, the outputs from the tone detector were coupled to inputs on the Memotech printer port, and then the Memotech ran the program to decode the signals."