Allllright, after a bit of a hiatus, trying to get back into things. “RL” has really been grinding its axe the last 6 weeks or so..
I'm tempted to knock out a little credit-card sized PCB of the power section, standalone; it would feel like progress, and present a nice little way to test without risking anything, and also be useful for other projects. Essentially a DC jack (with optional alternate pin header) for VCC in (such as 9V), feeding a 7805 regulator to get a nice 5V output; 7805's are cheap and omnipresent so handy to use, but they emit a fair amount of heat.. still, I do not expect to pull much amperage so we should be fine without a heatsink; testing will tell. The 7805 feeds in turn through a TI TPS7133 to get us a 3.3V rail as well, and no heat at all there; all of this carries out to pin headers to get us the VCC, 5V, 3.3V and GND power lines we need for the rest of the board. Completed by having a toggle switch so power can be enabled and disabled right on the unit and good to go.
After the power board, need to move onto the more useful and serious bits.. cartridge slot, GPU, audio, etc. And not to mention separate CPU boards for each CPU, so we can drop in an Atmel, Zilog or ST chip.
I do find it off-putting to have so many pieces needing custom components in the CAD, but its really not so much trouble as it feels in my head; sort of like taxes – doing taxes is quick really, but getting your nerve up enough to actually do them, is trouble. I was going to add power posts onto the power board instead of or in addition to the pin headers, but I just can't be bothered to modify Eagle config files to add a large drill size for knocking out the hole needed, and looking up if the boardhouse in question can actually support larger drill sizes, etc. But had to measure out and test and make the schem symbol and footprint for the toggle switch and DC jack. Upcoming is the cart slot edge connector, audio jacks and so on.
Actually laying down all the wiring and stuff is fun; layout out the pcb is fun but painful; building the schem symbol and footprints.. total drag.