mac_classic_crt_pi_hat: A repository from nilseuropa

Classic Mac CRT driver HAT for Raspberry Pi4

⚠️ Proof of concept running PoP on minivmac:

This method is utilizing the Display Parallel Interface of the RPi. The DPI device tree overlay has to be configured correctly to make this work. (For fine tuning, troubleshooting or more detailed explanation please follow the link in the credits section to nerdhut's original article.) ⬅️ KUDOS

Configuration

dtoverlay=dpi24
overscan_left=0
overscan_right=0
overscan_top=0
overscan_bottom=0
framebuffer_width=512
framebuffer_height=342
enable_dpi_lcd=1
display_default_lcd=1
dpi_group=2
dpi_mode=87
dpi_output_format=0x76017
dpi_timings=512 0 14 178 0 342 0 0 4 24 0 0 0 60 0 15667200 1

Schematics

Theoretically you can invert the data signal by just configuring the video hardware, but instead of that I have decided to sum the highest bits of the green, blue and red channels through an inverter IC. ( It could have been just 3 transistors. )

Board layout

The board has been quickly put together as an afternoon project. The goal was to quickly make a single sided prototype version based on DIP components. Feel free to edit the eagle source files included in this repository to your needs.

Top side

Bottom side

Build

As this was a quick and dirty build, I have just mounted the RPi with it's connectors facing outwards to a depron plate, held by a piece of aluminium angle that was lying around. This way I have access to the ethernet and USB ports.

I used a cheap SD Card extension cable, so that I can fiddle with the card without disassembling the whole contraption. ( I have reused the DSUB connector in my Apple // --- nothing goes to waste here ... 😄 )

Final result

Further plans ( big ideas, don't get any )

Currently the ADB connectors are hooked up through a microcontroller, that is totally unnecessary, the interface could go straight to the HAT instead.
An additional SPI USB controller chip could be added to the HAT, supporting USB-SCSI.
It would be nice to interface the floppy drive ( maybe through an integrated greaseweazle )
Another idea is to add an analog amplifier as well, so that the internal speaker is driven directly by the SBC. ( ... and the audio jacks )
The whole thing could go in place of the original motherboard, with the connector interface matching the holes on the enclosure.

Credits

Most credits go to nerdhut for doing all the heavy lifting. A truly elegant solution. 👏 https://nerdhut.de/2020/03/17/raspberry-pi-dpi-control-crt/

nilseuropa/mac_classic_crt_pi_hat