Oh, can't believe I hadn't even searched for Syntec here.
I have literally spent the last week looking for used SK panels and trying to figure out what's what with them.I would be very, very interested in hearing more about your exact board and what's underneath your Arduino and next to it.
Now, feel free to skip to the bottom as next I was asking questions that you have actually answered already - I just didn't know enough to realize:)
Skip From Here...
Newer SK panels have a small "matrix chip" surface mounted to the button side of the PCB (just inbetween button switches), older ones have a larger one on the backside (often a Holtek) and even older ones have a whole daughter board attached to the back side with a what Syntec calls a "decoder module". I always assumed the chip would spit out a proprietary serial link. I had no idea they were talking PS/2... Well, I thought perhaps the older ones were based on the Holtek model numbers.
But I have been trying to avoid newer boards because I wanted easy access to the matrix. I also had no idea the matrix is actually availble on the "HK Connector" - but that's how it looks from your picture. It looks like the Arduino is connecting to the HK. Or is the HK sending out PS/2 to your arduino? In which case your panel must indeed still have a "matrix chip somewhere" and your Arduino turns PS/2 into USB?
Also, how do you control the button LEDs?
If you could find time to share some more on how you made this work, I would be very grateful. I would mostly likely go this way as apart from ideally wanting more overide knobs, the SK4/6M panels have a really nice set of control buttons - plus the alphanumeric keys, too.
On a related note - as for turning the matrix into USB, when I asked AI about how to hack older SK panels it suggested this approach but to also make a combo USB protocol of HID plus a gamepad or joystick library. That way, supposedly, when doing the HAL connections you don't have to venture into weird combo USB presses to map the buttons that HID has no library for. So, you'd use HID for the regular stuff it already has and then gamepad library for everything "CNC" and it would just be passed through as button 1, button 2, etc.
Also, I did talk to a Chinese vendor had to check back with the factory on the protocols and how open they actually are but between the language barrier and me only wanting to buy one, he kinda lost interest, haha. But I think he said they could deliver bare matrix, USB-HID and more.
Skip To Here:)
[EDIT] I really should learn to read. You specifically explained the SK panel does both PS/2 and matrix. So, now I think the PS/2 signal may be coming into your arduino from that 5 pin connector in the corner of the board that says "to keyboard" and the matrix comes out of the HK Connector. Also, you even said the matrix is shared for both buttons and LEDs. So, there we have it:) What wonderful detective work you have done to make these panels work!
So... would you be inclined to share the code and pin mapping to help others along:)?
