Since we discontinued the RPi hat products, we've received many requests for continued production. To give back to the community, we've decided to open source the project.
Here's a quick and dirty guide for CRT options as of 2020. If you're CRT is YPbPr capable, get a cheap HDMI -> component box. Quality is very good and they can generate the correct sync signals as well as operate in 480i (which hats aren't capable of). You can re-tool any of the distributions for CRT use by modifying the appropriate lines in the config.txt to redirect video output back to the HDMI port.
If your CRT only supports RGB+Sync, you can use a HDMI->VGA converter. A passive sync combiner by connecting the H and V lines via a T splitter works on most displays. Note: I have never had an issue, but use with caution and at your own risk since the sync voltage is twice as high as normal.
You can also use the 3.5 mm jack for composite video output, but this will need a different software chain than the hat/HDMI options. Personally, I don't mind composite that much, but apparently I was flagged as a troll in a certain Facebook group for expressing the sentiment.
If you need S-video, composite, RGB with 75 ohm sync or multiple simultaneous output, then give the hat a try!
Here is a zip file with the Gerbers, BOM and HEX file for programming the PIC32 processor:
Update: Here is the schematic and source code for the PIC32 sync combiner:
Update: Here is the schematic for the analog and power sections: https://www.dropbox.com/s/n3s1tdl67hhq0un/RetroTINK%20Ultimate.pdf?dl=0
The PIC32 dynamically measures HSYNC lengths via its internal timer. During VSYNC periods, it stretches the length of the composite sync signal (generated by ANDing the HSYNC and a GPIO output from the PIC32). This allows the sync combiner to work at different line frequencies. At the same time, the phase (falling edge) of the CSYNC signal is always correctly aligned with the falling edge of the HSYNC signal.
I don't believe this works yet for interlaced video, but it has been tested at 240p, 480p and 720p.
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