Various ramblings – Electronics, radio, old computers, cars & other junk…

Tag Archives: 6502

Progress on the 6502 computer – Milling PCB’s

While work and other commitments have been sapping a large amount of my time I have been making slow progress with the milling of circuit boards for the 6502 computer project. I have added some pictures of progress below.

I am slowly getting the hang of repeatable and reliable results on the mill. Most trouble stems from the height at which the program starts: Cut too deep and the V cutter wears quickly, the tracks wander a bit (following the weave of the fibreglass mesh in the board) and the over all finish is poor. Cut too shallow and you might run into issues with track isolation.

I seem to have found a sweet spot for starting position and depth of cut specified in the GCode, there are methods for using a probe to set height but I have been using some thin thermal docket paper to test height. I carefully jog the Z axis down until the V cutter just cuts the paper without marking the surface of the copper, I hit the “touch off axis” button to set the zero position and then run the program.

I am still tweaking the design of the boards but I am very close to the final revision. Once this is done I can start milling the final version of the boards and begin construction.

Milled PCB Test

A few pictures of a test run trying out isolation PCB routing. GCode was generated using the PCB-Gcode script for Eagle, using the backplane board from my 6502 project as input.

Part way through the run I noticed that the mill was slightly out of alignment on the X-axis, this was causing shallow track cuts which got progressively worse the further along the X-axis the program went. A quick adjustment of the gantry seems to have fixed this but some further testing is required. I also need to tweak feed rates and cut depths, but the test went very well!

Etching boards – Round 1

My first attempts at etching these boards didn’t go so well. Using the toner transfer method has worked very well for me in the past, but it looks like my current printer doesn’t work as well as the one I used previously.

Below are a few pictures of the backplane boards I tried etching, the first photo based off a slightly older design with narrower traces. While the traces were etched fairly accurately, the surface of the traces has some fairly deep pitting where the toner coverage wasn’t thick enough. The worst of the pitting has eaten through to the fiberglass.

In some places the toner didn’t stick down very well, possibly because the board wasn’t clean enough or the toner hadn’t set properly. Ahh well, looks like more testing is needed.

While it is annoying to have wasted two boards worth of PCB material it is good to iron out these problems now. I have gone through all of the boards and increased trace width and also modified some packages to increase the size of pads and decrease drill size which should help with etching. Now I just need to improve the transfer process!

6502 computer project

While I was reading the Steve Jobs biography I was given for Christmas in 2011 I was feeling strangely nostalgic about the good ol’ days. This was strange mainly due to the fact I wasn’t yet born when the Steve’s (Wozniak and Jobs) were designing and building the Apple I & II…

Some time after that I read on Hack-a-Day about a 6502 based computer that Quinn Dunki was working on named Veronica, and instantly knew that I’d love to make something similar.

While not an exact copy of Quinn’s work, the design I have cobbled together does resemble hers quite a bit. My design is primarily based off of Grant Searle’s microUK101 design which itself is based off the UK101, a fairly early kit based machine. Both of those pages have huge amounts of information and are very well worth a read. I certainly read over them a fair few times to get my head around it all!

Just a few quick things, basically a warning to anybody reading this… I’m a “computer guy”, I earn a living working as a computer technician/network engineer. I have no formal training in the field of electronics (as I am very sure many of you will notice), most of this stuff is self taught. Accordingly, things on this page may be horribly wrong. If you do spot anything that is wrong, please let me know!

Building this computer is a way for me to learn more about electronics, mess with some hardware this is older than me for a laugh and have a bit of fun while doing it. If I stuff things up on the way to completion, hopefully I will have learnt something from those mistakes.

The 6502 computer project begins!

After reading over Quinn’s Veronica pages several times I started looking around for more information about various old CPU’s and systems I could base my own off. Very early on I decided on the 6502 as there were so many stable designs using it, and I figured this gave me the best chance of putting together a working computer.

After a fair bit of reading I decided on building Grant’s microUK101 design on a passive backplane borrowed from Quinn’s Veronica design.

After further research and many hours sitting in front of Eagle, the following PCB’s were created. Using the free version of Eagle was a bit of a challenge, the backplane just fits within the board size limitations.