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Classic Mac Video Signals Demystified Designing a Mac-to-VGA Adapter with LM1881
- artiscode 3y agoCan someone smart in EE explain why the author wants to avoid using a microcontroller? Cost per unit isn't an issue for this type of project, it makes things easier, allows to employ more advanced logic like sensing the monitor type to decide what monitor ID to send to the computer, you can have LED's and so on. It already requires 5V power for the chip, what would be the downside apart from added complexity?
- ianlevesque 3y agoSomeone was able to output 1080p(ish) with an RP2040, so yeah, it'd be doable. https://hackaday.com/2023/03/31/could-1080p-video-output-from-the-rp2040-be-possible/ https://hackaday.com/2023/03/31/could-1080p-video-output-fro...
- happycube 3y agoThe monitor signal is analog which means you'ld need a three-channel ADC to get it captured. might be able to do it with 4 or 6 bits per channel on a single rp2040, but you're probably getting into small FPGA (ice40?) territory there. Maybe an pi5 could handle all three channels in 8-bit, depending on how the RP1 actually works. I'm hoping that it can handle a 40msps 10-bit ADC - a Domesday Duplicator hat would be wonderful. The other option would be to find a vga->hdmi convertor that likes the signal coming out from this board, then you could plug that into anything modern. --- When I first saw this I thought it was about an actual 9" classic mac, which I guess would be useful but IMO those are really designed around the CRT too much to make a replacement 'fit' well.
- ianlevesque 3y agoMy approach would just be to sample one channel, like green, with the ADC and generate the sync signal, avoiding digital processing of the video itself. Just pass it through with any necessary level shifting in analog.
- happycube 3y agoThat'd definitely work.
- bogantech 3y agoRGBtoHDMI will convert the classic mac video to HDMI https://tinkerdifferent.com/threads/my-little-guide-on-rgbtohdmi-installed-on-classic-plus-etc.2475/ https://tinkerdifferent.com/threads/my-little-guide-on-rgbto... It is also useful for several other kinds of machines such as the Amiga
- artiscode 3y agoInteresting read, albeit the comments seem to suggest it's clickbait and a thought exercise, rather than a PoC or working solution. I was thinking more about an MCU that supplements the LM1881, not replaces it.
- bogantech 3y agoThe part where he talks about avoiding a micro is in regards to detecting activity on the various sync signals to turn on LEDs which is really simple and easy to do without having to resort to a micro The microcontroller can't really help deal with the dip-switch mess because it would have no way of sensing whether the monitor supports Composite sync/Sync-on-green etc
- squarefoot 3y agoShort of using microcontrollers or just discrete parts, the same function can also be obtained by less specialized chips such as the 74LS123. Here's an application schematic from Elektor. https://www.worldradiohistory.com/hd2/IDX-UK/Technology/Technology-Modern/Archive-Elektor-IDX/IDX/80s/Elektor-1985-07-08-OCR-Page-0083.pdf https://www.worldradiohistory.com/hd2/IDX-UK/Technology/Tech...
- ianlevesque 3y agoThe hero we really need, nice work.
- scelerat 3y agoScreenshots include cameo of much-loved (by me anyway) network tank game, Bolo. https://en.wikipedia.org/wiki/Bolo_(1987_video_game) https://en.wikipedia.org/wiki/Bolo_(1987_video_game)
- ianlevesque 3y agoHa nice. Programming 'Bolo Brains' or whatever they were was a cool challenge at the time.