The ZX-81 is small. Really small, as you can see in the picture above (although I must admit I have big hands). It has a tiny membrane keyboard which has four or five functions for every key. There is a lot of mode-switching when entering a program.
Since this was a real home-computer, it only came with an RF connector so you could connect it to your standard TV-set.Which is impractical in these days so I decided to modify it for composite video. Which is actually quite simple. The video signal is already there, it only needs a bit of buffering and you'll have to bypass the RF modulator. I got my instructions from here: "Adding a composite video output.", but of course I started with this illustrated step-bystep instruction on taking it apart. And what happens to almost everybody also happened here: the keyboard flatcable broke when I turned the PCB over. :-(
The video buffering circuit is really simple. It's just a NPN transistor and a 100 ohm resistor.
On the side of the RF-box there are all the connections you need
I cut the 5V lead close to the box, soldered it to the collector and finally cut and connected the video lead to the base of the transistor. And this simple mod works surprisingly good:
|Price [Original]||€25,- [ £69.95]|
|Processor||Zilog Z80 @ 3.25MHz|
|Why ?||Iconic, as being the first super cheap computer.|