A $5 Graphics Card For Homebrew Computers

While not very popular, building a homebrew computer can be a fun and rewarding process. Most of the time, though, the video capabilities of these computers is as bare bones as it can get – running headless, connected to a terminal. While this is an accurate reproduction of the homebrew computers of the 1970s and 80s, there’s a lot to be said about a DIY computer with an HDMI-out port.

[spencer] built a Z-80-based homebrew computer a few years ago, and while connecting it to a terminal was sufficient, it was a build that could use a little more pizzazz. How did he manage to stuff a terminal in a tiny project box? With everyone’s favorite five dollar computer, the Raspberry Pi Zero.

The computer [spencer] built already had serial inputs, outputs, power, and ground rails – basically, a serial port. The Raspberry Pi also has TX and RX pins available on the 40-pin header, and with a stupidly simple board that [spencer] whipped up in KiCad, he could plug a Pi into the backplane of his homebrew computer. A few setup scripts, and a few seconds after turning this computer on [spencer] could mash a keyboard and wail away on some old school BASIC.

This isn’t a use case that is the sole domain of the Pi Zero. A Parallax Propeller chip makes for a great video terminal with inputs for PS/2 keyboards and mice. A largish AVR, with the requisite NTSC video library, also makes for a great video interface for a homebrew computer. The Pi Zero is only five dollars, though.


The Raspberry Pi Zero contest is presented by Hackaday and Adafruit. Prizes include Raspberry Pi Zeros from Adafruit and gift cards to The Hackaday Store!
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39 thoughts on “A $5 Graphics Card For Homebrew Computers

  1. That really is kinda funny, using such a powerful beastie just to look at a simple system, but a good us for the Zero non the less..
    I just wish the PiZeros were available as I have some projects in mind.
    Years ago I made a memory mapped video display for my Signetics 2650 system, Originally it ran a 110 baud serial terminal. (My regret is I gave it all away.) The video board was made on Veroboard and I wrote it all in assembler, actually inputting the hex codes via the serial terminal. Those were the days. 11K (not M) of RAM made up of 88 ICs!

      1. I used the 6847 ( i beleave it was the same one as the trs 80 color computer) with a z80 cpu.
        I wire rapped the hole thing and had 16k of ram. I just came across the ram board the other month.
        those were the days.

        1. Yes, it was the 6847 in the Radio Shack Color Computer (until the CoCo III, when the used a custom IC that gave 80 x 24 video among other things). The original CoCo was very much like the “sample circuit” in a Motorola application note for the 6809.


    1. No, all the processing is done as it was before. The Pi is a $5 video card. How is the headline misleading? When you buy a Nvidia card do you calculate the cost of the motherboard as well?

        1. No, not what I was getting at. Just because the whole shebang puts out a video signal in the end doesn’t mean it is a video card. A car is not a $10000 set of wheels for shoes, an OpenWrt router is not a $10 network adapter for an Arduino, and a Pi Zero is not a $5 graphics card for another computer it is attached to as a terminal. That’s ass backwards and misleading wording, if not downright clickbait.

    1. Adafruit has them for $5. Shipping is a separate product with it’s own costs, but the Pi itself is $5. I’ve gotten two from them.

      I believe Micro Center also charges $5, but being in Canada I’ve never even seen a Micro Center so I can’t verify that.

  2. Ok people, I think there’s a bit too much hating going on. I don’t think a hack should necessarily be affordable nor the parts readily available. The guy built something himself, great. I do hope he’s going to upload his code to hackaday.io though, because right now I have no idea how he did it and how difficult it is.

  3. So he’s using a computer far more powerful than the computer it’s plugged into, just for the Pi’s video output capability.

    Sure. Makes perfect sense. Like using a chainsaw to cut weeds makes sense.

      1. Actually no. Its about using the right tool for the right job. Just because something is cheap(but almost unobtainable) doesn’t make it a good hack.

        I’d have been more impressed if the hacker went old school and took a Yamaha V9938 or similar beast and used it.

  4. Finally, a backplane arrangement! That’s how cheap computers should be made: want more speed? Change the update processor board, want more i/o lines? Just plug in a different i2c/spi/whatever decoder. Want nothing? (ie, Zero?) keep it as is. Too bad the Zero is and will remain unobtanium for a looong time.

  5. This guy made a nice little computer yet the article (and to be honest most of his write up ) is about how he plugged a PI into his serial port. if he had made it into some gadget class VGA device I would of been impressed but this is just gratuitous Pi mentioning …lets see the rest of the project and less of the Pi thankyou !

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