Home Made 8-Bit CPU Is A Wiry Blinky Build

It might look like a random pile of wires to some, but it is far from random: [Paulo Constantino] built this 8-bit CPU himself from scratch. He built his remarkable creation using wires and 74HC shift register chips, plus a selection of LEDs to show the various registers.

Running at a maximum of 5MHz, it has an 8-bit data and address bus, although the latter can be expanded to 16 bits. It’s not mining Bitcoin (yet), but it can do things like play the Mario theme. His latest addition is the addition of the ability to write data out to flash memory, and he is looking to add a keyboard to make programming easier.

At the moment, he has to program the CPU by setting DIP jumpers. It’s an impressive, if somewhat frightening build that [Paulo] says took him a couple of days to design and a week or so to build. We’ve seen a few breadboard CPU builds, (some of which were tidier) and builds with similar shift register chips, but this one scores big in the blinky light and mad genius stakes.

Thanks to [AnalogMind] for the tip!


39 thoughts on “Home Made 8-Bit CPU Is A Wiry Blinky Build

    1. Considering the capacitance between two pins in a DIP is about the same as between two lanes in the breadboard, about 4 pf, I don’t think that’s such a big deal. The wires are far apart and will contribute diddly-squat to the capacitance. But the killer would rather be wonky contacts, with that many connections one of then are bound to go bad by just looking at them – especially if one is using cheap ebay/chinesium boards. I guess the inductance in the long wires would also be a bit problematic if you want nice clean & sharp edges on your signals.

      1. Yeah, went through an amazing exercise many moons ago in school estimating stray capacitance and inductance of wire-wrapped circuits, and it was surprising.

        The gist, as I recall, was that the big old rats’ nests of wire-wrapped connections that we often made were actually pretty solid performers. It was generally the length of the wire itself that was the chief limitation on speed, rather than various impedance and coupling issues.

        1. Wire wrapped boards were space qualified for the Apollo project. You can’t get a better endorsement than that :-)
          The chief speed limitation is the chips not the wiring on a small board like that. Remember electricity only takes a nano second to travel a foot of wire

  1. What? How?

    How can this function? How was the cross-talk between the wires overcome? At 5MHz? I saw someone commented that might be a typo and was supposed to br 5KHz. Even at that frequency though… I’m amazed if this is real.

    1. You don’t get much cross talk because wire runs are not parallel for any distance. I built several computers in the early eighties using wire wrapped rats nest backplanes and they ran happily at 20Meg.

  2. That looks terrifying to debug. Wire-wrapping would be more reliable, but I don’t know if anyone still does that (and reliability probably isn’t the point of this build anyway.)

    1. I recently built a bit of test gear using a dozen TTL chips and I wire wrapped the whole project (except the power lines).. Comes a bit expensive but what price nostalgia :-)

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