Intel’s fabrication plants can churn out hundreds of thousands of
processor chips a day. But what does it take to handcraft a single
8-bit CPU and a computer? Give or take 18 months, about $1,000 and
1,253 pieces of wire.
Steve Chamberlin, a Belmont, California, videogame developer by day,
set out on a quest to custom design and build his own 8-bit computer.
The homebrew CPU would be called Big Mess of Wires or BMOW. Despite its
name, it is a painstakingly created work of art.
“Computers can seem like complete black boxes. We understand what
they do, but not how they do it, really,” says Chamberlin. “When I was
finally able to mentally connect the dots all the way from the physics
of a transistor up to a functioning computer, it was an incredible
thrill.”
The 8-bit CPU and computer will be on display doing an interactive chess demo at the fourth annual Maker Faire
in San Mateo, California, this weekend, May 30-31. It will be one of
600 exhibits of do-it-yourself technology, hacks, mods and just plain
strange hobby projects at the faire, which is expected to draw 80,000
attendees.
The BMOW is closest in design to the MOS Technology 6502 processor used in the Apple II, Commodore 64 and early Atari videogame consoles. Chamberlin designed his CPU
to have three 8-bit data registers, a 24-bit address size and 12
addressing modes. It took him about a year and a half from design to
finish. Almost all the components come from the 1970s- and 1980s-era
technology.
“Old ’80s vintage parts may not be very powerful, but they’re easy
to work with and simple to understand,” he says. “They’re like the
Volkswagen Beetles of computer hardware. Nobody argues they’re the best
but we love them for their simplicity.”
To connect the parts, Chamberlin used wire wrapping instead of
soldering. The technique involves taking a hollow, screwdriver-shaped
tool and looping the wire through it to create a tight, secure
connection. Wire wraps
are seen as less prone to failures than soldered junctions but can take
much longer to accomplish. Still, they offer one big advantage, says
Chamberlin.
“Wire wrapping is changeable,” he says. “I can unwrap and start over
if I make a mistake. It is is much harder to recover from a mistake if
you solder.”
Chamberlin started with a a 12×7-inch Augat wire-wrap board with
2,832 gold wire-wrap posts that he purchased from eBay for $50.
Eventually he used 1,253 pieces of wire to create 2,506
individually-wrapped connections, wrapping at the rate of almost 25
wires in an hour. “It’s like a form of meditation,” he wrote on his
blog. “Despite how long it takes to wrap, the wire-wrapping hasn’t
really impacted my overall rate of progress. Design, debugging, and
general procrastination consume the most time.”
The BMOW isn’t just a CPU. Chamberlin added a keyboard input, an LCD
output that shows a strip of text, a USB connection, three-voice audio,
and VGA video output to turn it into a functioning computer. The video
circuitry, a UMC 70C171 color palette chip, was hard to come by, he
says. When Chamberlin couldn’t find a source for it online, he went to
a local electronics surplus warehouse and dug through a box of
20-year-old video cards. Two cards in there had the chip he needed, so
he took one and repurposed it for his project.
The use of retro technology and parts is essential for a home
hobbyist, says Chamberlin. Working with newer electronics technology
can be difficult because a lot of modern parts are surface-mount chips
instead of having through-hole pins. That requires a wave soldering
oven, putting them out of reach of non-professionals.
After months of the CPU sitting naked on his desk, Chamberlin fashioned a case using a gutted X Terminal, a workstation popular in the early 1990s.
“Why did I do all this?” he says. “I don’t know. But it has been a lot of fun.”
Check out Steve Chamberlin’s log of how BMOW was built.
Photo: Wire wrapped 8-bit CPU/Steve Chamberlin
Credits: Wired.Com
