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Big Mess Of Wires Homemade CPU

Big Mess Of Wires Homemade CPU

Homebrew Oldschool Computer Processing Unit

A Californian videogame developer has built his own single 8-bit CPU using 1,253 pieces of wire, 18 months of time and around $1000.

The aptly named Big Mess of Wires (BMOW), made by Steve Chamberlin from Belmont, California, went on display with hundreds of other exhibits of DIY technology, hacks, mods and projects, at the Maker Faire held over the weekend.

Big Mess Of Wires

Chamberlin designed his homebrew CPU with three 8-bit data registers, a 24-bit address size and 12 addressing modes – a design which closely resembles the MOS Technology 6502 processor used in the Apple II, Commodore 64 and early Atari videogame consoles. Nearly all the components used to make the BMOW were parts and spares from the1970 – 1980s era.

“Computers can seem like complete black boxes. We understand what they do, but not how they do it, really…

“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…

“Old ’80s vintage parts may not be very powerful, but they’re easy to work with and simple to understand…

“They’re like the Volkswagen Beetles of computer hardware. Nobody argues they’re the best but we love them for their simplicity.”

Chamberlin started with a 12×7-inch Augat wire-wrap board sporting 2,832 gold wire-wrap posts that he purchased from eBay for $50. To connect the parts, Chamberlin used wire wrapping, a technique that involves taking a hollow screwdriver-shaped tool and lopping the wire through it to create a secure connection.

Wrapping at an estimated rate of 25 wires per hour, Chamberlin used 1,253 pieces of wire to create 2,506 individually-wrapped connections.

In an article posted on his blog Chamberlin wrote:

“It’s like a form of meditation. 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.”

Wire wraps are less prone to failure compared with soldered junctions, but they take much longer to complete. Nevertheless, they still offer one main advantage says Chamberlin:

“Wire wrapping is changeable…I can unwrap and start over if I make a mistake. It is is much harder to recover from a mistake if you solder.”

Finding all the parts to build the CPU was relatively easy, although the video circuitry, a UMC 70C171 color palette chip, was hard to come by. After having no luck searching for a source online, Chamberlin went to a local electronics surplus warehouse and dug through a box of 20-year-old video cards. In the end he found two cards that had the chip he needed.

Steve Chamberlin Creator Of The Big Mess Of Wires

Steve Chamberlin Creator Of The Big Mess Of Wires

The development of the BMOW didn’t stop at the CPU. Chamberlin went the whole-hog and added a keyboard input, an LCD output that displays a strip of text, a USB connection, three-voice audio, and VGA video output to turn it into a functioning computer.

After months of the CPU sitting naked on his desk, Chamberlin finally fashioned a case using a gutted a popular 1990s workstation, the X Terminal.

“Why did I do all this?” he says. “I don’t know. But it has been a lot of fun.”

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