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 28 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 definitely 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.

2008: Atmel AVR Printed Circuit Board

I read about the Toner Transfer PCB technique, and I wanted to have a go. I have plenty of copper-clad board from way back in the 1970s, I have ferric chloride etchant, and I have a laser printer. All I needed was a design, and the Atmel AVR seemed like a good chip to base it on. Then, I spotted the Evil Mad Scientist Labs business card PCB and I realised that this was what I wanted to build. But the original card was not designed for toner transfer, and I could see some ways to improve the design, so I made a version of my own, and that's what you see in the photos here.

2008?: Another Atmel AVR Prototyping Board

When I got the parts for the ATmega8 boards, 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, probably with another toner transfer PCB. 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 from Motorola and ST Microelectronics) as well as some rare Hitachi HD6309 chips and the required RAM, EPROM and I/O 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.