I am intrigued with the switch circuit you mentioned. I would think it would have to be automatic, sense type switching circuit right....? I'd hate to have to run more wire from the external connector to the switching board.
How's the clearance from the cart connector towards the middle of the board? Height and width clearances... The version in the photo seems to hang off the wrong side of the mainboard.
Hi Dropcheck. The switching circuit is manual and requires a system reset after selecting a new cart (or none). Not sure how automatic selection could work, if four carts are installed at once as the original design allows for. It maybe could be changed to a software selection but would require mapping a register, so more chips. Or an expanded TK ][ re-design but that would be asking a LOT from Michael so unless this mod is wildly popular, manual monetary buttons will work.
I routed a switching board based on T0ri's circuit-
Here is the OSH Park Gerber view, but ordered from Seeed studio. IC1 is the '244 switch for the FP cart socket and IC2 is a '174 quad FF selector circuit. I was only planning for a A/B switch but went with the 4 cart option as it may be more useful.
I followed your vertical mounting idea and will use RA SIP sockets (on the 30p footprint at the top of the board as pictured) to mate with the pins on my XEL but could be changed to edge fingers. The 2x5 header is for the front panel LEDs and switches and the (bottom) 30p is for the FP cart socket. The 34p header is to connect to other controlled 'carts'; I'm routing an internal SIC cart board that includes it's own control '244.
Here is the SIC board, still reviewing the layout-
Horizontal mounting would need more height (about 15 mm above the XEL board, min.) if over hanging to the right; to clear the lower PoKEY, it has stacked sockets to allow for the PIC under it. There also might be a space problem with a Rapidus installed (or the M-PBI FM sound board I'm working on). Overhanging to the left is OK in my user case but would be a problem for someone using a mini-ITX case, so vertical seems the best choice.
So once the boards start showing up I can start testing