I’m considering adding a custom serial-based protocol to Eyesy. I think it could be possible by repurposing UART connection used for serial MIDI. I mostly understand what needs to be done in software part, but I’m not sure about some hardware details.
AFAICT, MIDI uses first UART port that is connected to GPIO 14/15 of RPi Compute (pins 51&53). I’ve found that there are exposed vias connected to those pins that should be fairly easy to solder to. But I’m not sure what is TX line connected to.
Can I get a confirmation that I’m looking at correct UART pins and won’t summon The Dark Lord himself by using them?
Sounds interesting… what will you be connecting to the EYESY?
Assuming you are sending from a microcontroller like Arduino running at 3.3V or 5V, you shouldn’t need to solder anything to the EYESY board… you can just send serial data into the 1/8" jack and as long as the software / baud settings are correct you should be able to receive just fine. If your source is an old time serial (RS-232) cable, you would need to convert to TTL.
The hardware that runs on the other end is STM32 MCU on Rebel Technology Owl & Magus. They support a UART based protocol for sending device parameters, buttons, custom commands, messages, data or passing MIDI. It’s not enabled in their official firmware and has some issues, but I’m working on reanimating it.
Another interesting thing about this protocol is that it can be used as a ring bus, with one device forwarding data to next one.
The protocol is bidirectional, so I’I need both UART RX and TX lines, while there would be only RX data coming from MIDI input. That’s why I’m trying to figure out what happens to this UART’s TX line. Also, I’m not sure if optocoupler on Eyesy would work reliably on 115200 baudrate, so I may have to bypass it.
USB UART port would certainly work, in fact I’ve already though about using it to avoid any hardware modifications until I have the software part working. But I would prefer to end up with hardware UART and USB port available for other duties.
I thought that TX line was connected to something when I’ve opened up Eyesy, but apparently I’ve looked at the opposite side of SODIMM slot. So if I’ll want to use hardware UART, I’ll have to solder RX line to via and TX line to SODIMM connector.
Anyway, I think I have all my questions answered for now, I’ll update this topic when I’ll make some progress with this project.