For about 11 years I worked as an analogue RF design engineer at a company. In the later years some of the analog circuitry moved into the digital domain with help of DSP’s and/or FPGA’s. I found FPGAs more interesting and I wanted to learn the VHDL language to be able to do RF DSP technics in FPGAs.

At a certain point when I feel more comfortable with the VHDL language, I wrote a simple CPU core and it works! From that moment I getting more and more interested in how CPU internaly works. I searched the web for the early CPUs/computers because I expected that they are simpler and better to understand then the latest CPUs on the marked.

Tip If you designed your own CPU than probably you are interested about target less compilers. If so, then take look at the end of my links page.

I was impressed on how to operate an old computer with all those lamps, switches, papertapes, etc….

Then a question came, shall I make a CPU with TTL chips like the PDP-11/44? There is a big disadvantage: more and more TTLs chips getting obsolete.

Then the next question came, shall I make a CPU with through hole discrete components like the pdp-8? I think discrete components will not completely disappear. Maybe through hole, but than we can move to SMT.

I looked at some pdp-8 "straight-8" pictures on for example this site:

That’s a little bit too much I thought. But despite the pictures I started to make some dead bug DTL’s to "play" with it. Very funny, with very few different components I can make all sorts of digital circuits. That will reduce costs because I have to buy a lot of the same components.

Then a colleague notest me on a cheap PCB fusion service which uses standard PCB board sizes to keep prices low. Lets see on how much transistor inverter circuits fits on 5x5cm with a 2.54mm pitch. Eight, a nich number! Even more nicer, all connections are on one site and one hole left!

Then the idee was born, put a 2.54mm pitch trough hole ring on the board edge. Then I can stack four boards with a 90°C twist, which can be laced together with solid copper wire. This is a nice compact construction and cuts connector cost.

Now it seems feasible to build a computer from it with not to high costs.

We shall see ……