Computers I Have Built

1979: Acorn System One

A 6502-based machine, built when I was electronics lab technician at school.

1980: Compukit UK101

Another 6502-based machine, built from a kit. Still working 27 years later.

1984: Z80 Board

A college course project, based on the Z80 and built using wire-wrap. I never really got enthusiastic about it, largely because of the Z80 processor. All project work at the time was required to be based on the Z80, but I'm a Sixer, so I never liked it. It was supposed to be initially just a Z80 with some memory and a serial port, then you could add a matrix keyboard and a video circuit to make a terminal.

1992: 386SX-25 PC

Oh how dull, a 386 PC clone. I put a motherboard in a box; how can that count as building a computer? Anyway, it's junked now, having never run a single byte of true 32-bit code in its life. I still have the motherboard, in the loft, and an AT-style mini tower case that I painted black.

1994: Transputer Board

I've always liked the M212, it's my favourite transputer. So, I used an M212 to build a QIC-02 tape drive interface. The M212 was a transputer with a built-in MFM disk drive controller. But it had a mode switch that could change the disk controller into simply a pair of parallel ports, right on the CPU chip. I used it in that parallel port mode with one port used as the QIC-02 data bus and the other for all the handshaking and control signals. I wrote an occam program to drive it all, which booted over a transputer link (from an Atari ST) and ran in the M212's internal 2k memory. That 2k included a 512-byte tape block buffer!

1997: Transputer Serial Interface

For Submetrix, I put together a design for a T225-based four-port serial TRAM. We used them for a while in the sonar systems as interfaces to the GPS navigation receiver and the motion reference unit. I chose a Philips four-channel UART chip connected to the T225's external bus, along with some SRAM. The driver software booted the transputer via a link, and then sent the serial data in and out via the same link.

2002: PIC-based Prototype

For Mobile Bristol, I worked on some prototype PIC 16F876 designs. They were built as plug-together wearable computers as part of the research project. The master PIC was connected to the host (an HP iPaq) via a serial port, and slave CPUs were attached to it via an I2C bus. Having done that, I've decided that the PIC must be an "Eight" processor, because I didn't like it.

2005: Atmel AVR Prototypes

In my new job, I was asked to build a small embedded system around a microcontroller chip. After using the PIC previously, I decided to use an Atmel AVR chip this time. The little circuit went together pretty well, and connected up nicely to a PC's serial port. I have loaded it with code written in assembler as well as code compiled from C (with the WinAVR package, a version of GCC). I also built an AVR-based kit from EDTP which combines an ATmega16 microcontroller with an ethernet chip.

2005: Atmel AVR Robot Controller

Just for fun, I bought a ready-made Atmel AVR board that was designed for use as a robot controller. It has an ATmega8 chip, plus a clock crystal, reset button and programming connector. So far, it's just been plugged into a solderless breadboard, but I've managed to get it doing some whacky things (entirely in assembler). I've connected an HP four-digit alphanumeric display (HPDL-1414), a Super Nintendo joypad, a radio-control servo, a DC motor and an LCD module. I think the next things to add will be an analog voltage-divider for push-button control and an MMC interface. Well, after all that, I think the AVR chip is definately a "Six".

2006: Atmel AVR Prototyping Board

Another fun project, again using an Atmel AVR microcontroller chip. This board is loosely based on the Arduino. I've arranged the board so that I can plug in small daughterboards with LEDs, switches, motor drivers, and so on. The connectors also supply power (12, 5, 3.3 and -12 volts). Future plans are for a dual DAC board and an LCD board.

2007?: Another Atmel AVR Prototyping Board

When I got the parts for the ATmega8 board, I also got an ATmega32, which is a rather more powerful AVR chip. It has four 8-bit I/O ports, and it's in a 40-pin DIL package. The plan is to build another prototyping board with the ATmega32. Watch this space...

The Ones That Got Away

I've always wanted to design and build a 6809-based machine. I now have a fair number of 6809 chips (2MHz bus versions) as well as the support chips. Maybe this one'll get built after all...

I bought a 68020 development kit way back in 1986 with the intention of building a machine around that chip. Of course, I never did, mainly due to lack of spare time now that I have a career in the computer industry. I still have the chip, though, and modern CAD might just make a 68020 design feasible.