I wanted to build myself an A/V adaptor for my C64 for more than half a year already, but it was not easy to find a suitable DIN-Connector for that. It is important, that the connector sits in the computer's "VIDEO" jack well, does not fall out and does not hang down, just being held by the pins. This would apply stress to the contacts of the video jack.
"Ordinary" 8 pin DIN plug ("horse shoe" configuration)
First, I thought, that a panel mount connector would be ok and I have ordered a Lumberg SVG 80. It is nice for panel mount applications and not really cheap (€3,99 from reichelt.de). The problem for my application was the short cylindrical flange around the pints. This is suitable to inserting a cable mount DIN jack, but when I have connected it to the C64, it was almost falling out. One could have machined this plug, but that would increase the cost and reduce the group of people, who are able to build it, drastically. This is not my goal!
Lumberg SVG 80
So, the idea of an A/V-adaptor had to bake a bit further "in the project oven". Finally, I have found a suitable DIN-plug (the Lumberg SV-80).
It is not a cheap connector, well, it cannot be! Pretty many parts. But is has this beautiful insert, which sits well in video jack. It is quite hard to get out, if you only insert the insert. The solder cups for the cable are long enough, too. "This is a Bingo!", I thought. Do you say "This is a Bingo"?
I had found the pivot of this project. The rest was just work. First, I had to create a footprint for it. I knew, I wanted to install the plug with some distance to the board and it should be soldered as vertical as possible.
(Eagle) footprint for the insert
I do not like long pads for footprints, because they consume too much valuable real estate on a PCB. Space, that can easily be used for layouting the signal traces. But in this case, I have decided for the long pads, because it would be easier to solder in the connector from the side, where it sits (in a distance).
Soldering of the SV-80 insert
To illustrate my thoughts on soldering the insert, here is an early view of the finished PCB.
The schematic of the A/V-adaptor is pretty simple. I wanted to provide some options, like making use of the Audio Input of the C64 (which is only an analog input, that it run through the filter, it is not for sampling), also, a stereo SID option should be served (the FPGA SID also has a stereo output).
Schematic of the A/V-Adaptor (click to enlarge)
Jumpers on the PCB provide the optional configurations. The second audio channel ("stereo") is usually connected to pin 7 of the C64 video jack, as suggested by the FPGA SID manual. The 5-pin C64 and the VIC-20 do not have this option. For a mono output, both RCA-jacks (Audio Out L and Audio Out R) are connected to the single C64 audio output to make the mono signal to appear in the middle.
Some C64 have a LumaFix64 etc. installed, which reduces the Chrominance signal to a level, that better fits the standard S-Video Chroma signal. The C64 was invented, before the S-Video standard was defined, so the chrominance signal is too high, causing different problems with the color appearance on modern monitor equipment, like over-saturated colors etc. In these cases, the 330R resistor can be bridged with a jumper. This 330R resistor is commonly used in A/V cables, but I think, it is not necessarily the best value. I am planning to put some more time and afford in finding a better value.
A/V-Adaptor pcb layout (click to enlarge)
The final board design was done in a few hours, it was a bit of fiddling to find a good geometry, at least one, that does not cover other jacks on the backside of the C64. I have seen pictures, that prove, that it even fits with an SD2IEC (no cable version) plugged into the Serial Port. It does not match the C128, though, but I have seen, that Commodore4ever has made one from my design, which fits the C128.
The prototypes had to wait a bit, since I did not want to order just one PCB from China, instead of ordering more different PCBs. So, in October 2019, I have finally received the PCBs and could hardly wait to assemble the adaptor. It was the first thing, that I have built from all the PCBs, that arrived from China that day.
A/V-Apaptor PCB in the VIDEO jack of the C64
The board worked well with the standard cables (Audio/Composite and Audio & S-Video), that I have bought. The display looks great and I would consider it a success.
In the design, I did not care for matching impedances of the copper traces (this is called a strip line). The C64 is also not designed for, so the few centimeters of traces on the adaptor would not harm the video quality.
After the PCB, there came a 3D printed case. I did not have a 3D printer, when I had finished the layout in May 2019, so the board was not optimized for such a case. Hence, the resulting case is not perfect, but it works absolutely ok.
I have constructed it with Fusion 360, which I had started to learn just a few weeks earlier. I am used to draw 2D constructions for many years, so the step towards the 3rd dimension was not very hard.
The A/V-Adaptor case in Fusion 360
The distance between the PCB (solder side) and the case of the C64 should be as short as possible, so I decided to make a groove for every solder joint in the bottom shell. It was not really hard to do so, because I have exported the DXF-files (that is a Drawing eXchange Format for 2D drawings), which included the solder pads, so I just selected those and made then "a bit deeper".
Also, I wanted to have some labels, that can be placed on the top shell. I have exported the outlines of the top shell to a DXF file (again!) and imported it to Inkscape (a freeware graphic software). After a short time of fiddling, I have printed the label on paper, put an adhesive transparent foil on top and double-sided tape on the bottom side of the paper. This is, what I usually do for labeling front panels and cases, but it did not look very good.
So, I have found a laser printable foil, that is intended to be water prove, that is already adhesive ("HERMA 9500 Wetterfeste Folien-Etiketten DIN A4") on amazon. I am sure, there are other brands, that work as well. I am quite happy with the result. Cutting out all the jacks from that foil is a bit of a drag, though.
The A/V-Adaptors for the regular C64, the 5 pin C64 and the VIC-20
This project is available on GitHub. I have seen a couple of people are building them for sales. Please, do not request me to sell one for you, I do not have any spare ones and it is not my intention to produce them for selling.