Closed stevexyz closed 5 months ago
That is an interesting link to the composite video output. It looks like it would need two pins for video (sync and data), both requiring resistors. There would also be two pins for the stero audio (1 if mono was used), also requiring resistors. Then 4 GPIO pins for the SD Card (plus 3.3V and ground), so 7 or 8 GPIO overall.
At that point I think some form of carrier board would probably still be useful? I can see why the wespi could be "bare", as I think it is connected to the ZX81 pcb via wires, but I would be concerned that a "bare" Pico with keyboard, video and audio connections might be very fragile?
However, with only 7 or 8 GPIO lines used there would be enough GPIOs free to connect a ZX81 matrix keyboard, so I can see that a custom carrier board to support composite video + audio + SD Card + keyboard matrix connection may be an interesting solution. Perhaps something like the Cytron Maker Pi Pico board could be used as the basis of a prototype board for that? Alternatively there are hardware solutions for the ZX Spectrum Pico emulator that support VGA, audio, SD Card and keyboard matrix, so using that hardware design may be possible.
"Bare" solution could be an option (and I would go for it). Also SD card might be avoided since input can be taken from cassette (or tapeduino/wespi alike). So few resistors attached directly to wires/connectors and that's it.
If a "carrier" has to be setup then probably putting also the 40 keys for the keyboard on it would be nice (adding something like https://github.com/swetland/zx81-keyboard, maybe usable also with a real zx81, or as a PC keyboard, as a "triple function" with one board), but I would still prefer the bare version!
I am trying to understand what the reason behind the request for a "bare" solution is. Is it:
My thoughts…
The idea was exactly "to achieve a simpler and more cost effective solution".
I have now added support for LCD, VGA and HDMI. I have also added code for the colour Chroma card. I have received no more requests for composite output, and no pull requests offering code to support it, therefore I am closing this issue.
Since the ZX80 and ZX81 have just black&white video output all the circuitry of VGA (mainly resitors to mix the colors) might be omitted using just one of the analog pins (analog just to generate proper front and back porch). Probably a simpler output in any sense might be the composite one with just two wires. Also the same for the audio. See for example the wespi ZX81 addon, just the bare ESP32 and some little components. Maybe one or two resistors should be attached to the cables, but there should be no need of an external board... Not sure how to program the 2040 "coprocessor" but should not be difficult for the expert to adapt. What do you think? PS: I've found also a working instance to take inspiration from https://areed.me/posts/2021-07-14_implementing_composite_video_output_using_the_pi_picos_pio/