Friday, December 24, 2010

PCB Design

I've decided to suck it up and start figuring out how to do full-on PCBs for the remaining components. Soldering the wires by hand works well enough for things like the clock unit, but my experience on the program counter has been exhausting.

After quite a bit of tinkering, I managed to persuade the gEDA Suite of open-source EDA tools to do my bidding. Today I drew up the schematics and a PCB layout for the instruction buffer unit. This unit is very simple -- it takes the 24-bit instruction as input, then routes it through a pair of 20-pin headers (for attaching the logic analyzer), then on to a set of transceivers, which will actually be driving the bus. The entire layout has only 11 components on it, but as you can see, it's a very complex design:

Now I just need to procure some photo paper, gain access to a laser printer, and then I'm off to printing my own PCB! The guides online are all the same -- it's a simple process:
  1. Print the mirror of the solder layer on heavy, glossy photo paper in a laser printer. The toner will adhere, but will transfer to the copper easily with some heat.
  2. Clean the copper board thoroughly, removing all oils and dust.
  3. Lay the print face-down on the copper, hold in place, and use an iron to heat the toner and transfer it to the copper.
  4. Soak the PCB in the chemical bath stuff to etch the copper away
  5. Rinse and clean the toner off of the traces
  6. Use a dremel or a small drill to drill the holes (drill press is appaently the best for this).
And that's it! I can't wait to give it a try and see how my first PCB turns out. I'll keep you posted here.

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