So, having had a few fairly intensive days working on PCB design for my RC2014 computer, today was pretty much a day off. Apart from daily household chores, all I got done today was this;
Now, to the untrained eye, that may look like a schematic layout for 4 8×8 LED matrix displayed connected to a Z80 bus via some 74LS374s.
But it’s not.
It’s me tinkering on my day off. Ok, so I looked up the spec on the CSM-88041 LED matrix displays (which were manufactured in January 1998, so technically qualify for Retro Challenge) and worked out how I’d connect a bunch of them up. And, yes, I may have checked if KiCad had a 8×8 component already in it’s library that I could use – it didn’t. So maybe I might have practised my skill of component design.
But, other than that, I didn’t do anything else except for sit back and watch YouTube videos. Sure, they were videos on running data buses in KiCad, which I knew nothing of before. And, sure, I tried my hand at this data bus lark to see if it would help in linking up a whole bunch of matrix displays and tri-state flip-flops (it would!). But, really, it was just for fun.
But it does give me food for thought as to how I’m going to connect all the matrix displays up. To keep PCB costs down, it would be nice if each 8×8 matrix was on it’s own individual board that daisy chained to the next. But each matrix needs 1 ‘374 and an extra ‘374 for the whole bank. Plus a 74LS138 is needed for every 8 ‘374.
7 displays could be enough to achieve what I want. But the tub at the hackspace has a surplus of around 200, so using 7 is hardly making a dent, so maybe 15 or 23 might be more appropriate.
I’ve just got to come up with an efficient scheme for the PCBs. And soon. Or else I’ll miss out on the Retro Challenge deadline of the end of July. And if I’m able to make a good generic PCB for these displays, maybe others at the hackspace can make use of them too and build something useful from them!
Most likely, though, is I’ll end up doing this part on a breadboard with hundreds of jumper wires. Watch this space…