Finally, the VIC-2020 is working well and is far enough along where I can publish all of the project materials. The board works great and has passed all of my initial tests. I really like the Cherry MX keyboard and the custom printed keycaps.

All of the KiCad files, Gerber files and the Keycap art is located at:

https://bitbucket.org/danwerner21/vic2020


There are some project docs that describe the differences from the original VIC-20 and give some general information on how to build the system. ONE NOTE THOUGH -- the 3d printed case is still a work in progress (and will be for a few more days) do not print the STL files that are in the project as the boards will not quite fit in them yet. Will post again once the case is complete and ready to print.

Please feel free to reach out with any questions.
Dan Werner

PS -- I apologize for the flipped images, I have tried several different ways, but the board seems to insist that my images get posted filpped

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Dan Werner

Congrats on rolling out the VIC-2020 just in time! And thanks for the pics. The boards look fantastic.

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C74-6502 Website: https://c74project.com

On flipped images - if you click on them, they come out the right way up. I think they have been rotated using EXIF metadata, which the thumbnail generator ignores. To make the thumbnails come out right, you need to find a way to "bake" the rotation into the image data itself.

I know the VIC20 only by name and reputation, but this looks very cool and impressive.

I had the same issue when reposting a photo and happened to have a Windows 10 box nearby, so I tried opening the image with Photos (I think this is the default Windows 10 app for viewing images), which showed it in the correct orientation. But rotating it 90° four times, which brought it back to the starting orientation, and then saving it produced an image that seems to have the orientation correctly "baked in."

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Curt J. Sampson - github.com/0cjs

Ok, this is kind a design-history question on the VIC-20, so not sure if it's "hardware" or not. I just finished fixing up a set of schematics on the VIC-20 (Revision N schematics) in preparation for another project. I'm getting design rule errors on the two address buffer LS245 chips, so I dug a bit deeper on it. Commodore used two LS245 octal bus transceivers (set to go only one way) to replace (or as an alternative to) an LS244 octal buffer/line drivers.

Anyone know if there was a reason for this? I know sometimes Commodore designs were influenced by parts cost and maybe the desire to reduce stocking different parts? Any idea?

I would add that if you look at the hand-drawn schematics, the "A" and "B" columns are drawn reversed vis-a-vis the pins (i.e., the "A" column has "B" pins). This makes me wonder if at one point they used LS244's "A" on the CPU side would make sense.

I did a test plot and have the VIC-20 on an S-100 sized card (10" x 5"). PDF's {hopefully} attached. The cartridge port is a beast because of the clearance needed. Anyway, take a look. Thanks to Steve Gray for the original KiCad schematic files!


Thanks!
Rich

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org

My belief is with the LS245, the inputs are on one side of the chip. The LS244 has input, output, input, output... on each side. The LS245 just makes the design easier for them.

Good point. It actually alternates in groups of 4, which I didn't notice before. Then, yes, I'd agree that's probably the reason.

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org

I've spent the last few weeks fine-tuning the re-design. There are way too many chips to fit on an ECB-sized board (basically 4" x 6"), but it does fit on an S100-sized card (10" x 5"). Attached is a screen-shot of the board before placing the ground/VCC plane. It's fairly dense, with about 1100 inches of traces and 188 vias on a double-sided board. It has holes for an EMI cage around the video chip, a cartridge slot, and the "original" NKK rocker power switch. The only compromise, really, is the user port, which was downgraded to a 0.1" shrouded header. Maybe once I see how things fit on a prototype board, I might be able to squeeze the cartridge port over and move the user port.

Anyway, take a look. I will order a few prototypes and see how it goes.

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org

Boards received today from PCBWay. They look good. I might try to increase the trace margin around the edge of the board...there's a few traces that I feel are too close to the edge. Gotta figure out how to do that.

I think I have a spare VIC20 in the attic I can pirate for CBM-specific parts. Otherwise, the only tough chips to get are the LS133 and any of the non-LS stuff. But, the only chip I didn't have "in stock" was the LS133. Other than that, I have to order a few random passives that I didn't have and a power switch.

On to building!

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org

Yes, the older 133 logic gates are hard to find. I have 5 Vic-20 machines... 3 of them I did full sockets and replaced most everything with newer CMOS HC series chips. The one chip that can't be replaced by an HC series is the 7402 used for the 6560 clock oscillator.

In any case, I purchased a small quantity of 74HC133 chips some years ago.... which probably makes it more difficult for others to find them:



Shoot me a PM and I'll send you a couple. Do post some pics of the new PCBs.

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Regards, KM
https://github.com/floobydust

This is the bare board; hard to get a good picture because of the glare. I fit it on an S100-sized card (10" x 5"). I just ordered a bunch of stuff from DigiKey to round-out what I needed. I do so many projects that I have a huge store of random parts. Then I have to dig out a VIC from the attic. I seem to have more C64's than VICs for some reason (I wouldn't mind getting a working but ugly-looking VIC as another spare).

At the last minute, I added four anchor holes around the video section in case I wanted to put an EMI cage on it. Not like I'm selling them in a store or anything, but it did lend to the authenticity

@floobydust -- I'll PM you. Thank you for the chip offer.

UPDATE: Bad news...cartridge connector is mirrored so it won't work as-is. Arrrgh. I think I can just mount the connector on the bottom just for testing, but what a PITA.

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org

TI 74ALS133 still is in production (year 2021), ca. 3.32€, available at Mouser and DigiKey.
//Digikey also has TI 74F133 and 74S133 from Rochester Electronics.

Signal traces are way too close to the edges of the PCB indeed, IMHO this needs to be fixed.

Would suggest to add a TVS protection diode and a not too small (axial) electrolytic capacitor to the +5V power supply
(there is enough free PCB space between expansion port and power connector),
and to add protection diodes to the IEC bus (1N4148 or such) to prevent damage when hot_plugging the cable.
//Would it make sense to buffer the /RESET signal to the IEC bus ?

I made the design right from the VIC20CR (cost-reduced) schematic, so I was just picking the logic families right from that. I'll make a note in the BOM. I don't immediately think to substitute families if I do a re-creation, so thanks for mentioning it.


I'm doing a re-route of the board now. Apparently KiCad doesn't really have the ability to limit how close to the edge, so what I've read that some people do is widen the thickness of the edge cut to 2x the desired offset under the theory that the board house will trim at the center of that line. That didn't work for me so I just went with a keep-out area of 15 mils.


Regarding the capacitor, the original design had two different supplies -- the usual 9VAC and a dual-output regulated 5V and 9VAC supply. 9VAC isn't used in this recreation because there's no cassette port. The single-supply one had a 4700uF cap and the dual had a 100uF/16v on the 5V and 2200uF/16v electrolytic on the 9V (for the cassette motor. I added a 1000uF/16v radial cap.

I never looked into TVS or using fuses, although I see Commodore did use some input filtering on the 5v which I seemingly ignored when I re-drew the schematic (two small caps and an inductor). So, I added that. What's not in the circuit is any reverse-polarity protection which wasn't an issue with the prototypes.

Regarding the IEC bus, the VIC-20 line didn't use anything other than a few ferrites. On the C64 design, Commodore added 1N4148 diode clamping on the four primary signals and one in-line on the /RESET line. I don't think Commodore ever buffered /RESET but I would have to dig through all of the schematics to be sure. I know on the C64 they did not.

While on the topic of the cassette, is there a way to use a regular tape player with the Commodore machines? My thought -- and easy to add -- is if a regular cassette player can work (or an MP3/WAV source) in lieu of a Datasette, then I could add that to preserve some cassette capability. ISTR a circuit LONG AGO which could do it, but I can find it. I converted most of my tapes to WAV files as a way to preserve them.

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org

It's been a year since I've updated everyone on this project. After building it, I had some serious screen corruption that it took me a while to figure out, and naturally, other projects got in the way. It turns out there is an error in the originally-transcribed schematic regarding the memory read/write signal which, when fixed nearly made it work perfectly. I also had a corrupted ROM. So, after fixing both, it works great! Very happy.

Right now, I'm making a "revision C" which fixes that error, re-spaces the connectors to match the original (more for esthetics) and adds a card-edge for the user port on the left side. The board is prototype width (5.375") but shorter (10"). There are some compromises due to the size: the expansion port is vertical rather than horizontal (this saves nearly 2" of board width), the user port is on the side of the board, and there is no external cassette port (it instead relegated to a 1x6 0.1" header). I'm using a Penultimate cartridge and an SD2IEC adapter so I don't think the vertical expansion card is the hugest deal. The downside is that you'd need to make a custom multi-cartridge expansion (which is what I did back in 1982 for my own VIC; wire-wrap too. Still surprised it worked).

I have mine mounted on wood like the original Apple I and I'm using Dan Werner's keyboard reproduction (which is excellent, by the way); I attached a picture from my bench. All in all, pretty happy with the result.


Rich

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Rich Cini
Build Master and maintainer of the Altair32 Emulation project
http://cini.classiccmp.org
http://altair32.classiccmp.org