OPL3 ST cart schematics ready!

Schematics ready, routing and component placement just barelly started.

I’ve made some more on Atari ST OPL3 cartridge project. After going back and forth I’ve finalized schematics and began creating pcb layout (I don’t like this stage (boring!), so it will take me awhile). I try to do this cart as small as I can (currently on screenshot it looks like train, but it’s just a phase ;) ). This time I went with majority of SMD parts, several are still THT (mostly socketed, so they will be easier to repair without soldering). After that I will produce prototype boards to check it’s operation (5 pcs max), test them, fix potential issues on pcb if any and send gerber files to pcb manufacturer (still not sure where in what amount). Need to source parts to assemble first small batch too (if there will be interest of course) and start to think about suitable cartridge cases and labels. Of course I will need to finish suitable drivers, but this is the easiest part of whole project.

Board will have stereo line in (to provide sound from external source e.g. Atari), stereo output (I’m still thinking about adding another headphone output with potentiometer, but this will increase overall production cost and probably board size) and hardware reset button (after experimenting with OPLxLPT devices turns out it’s good to have one as an emergency). Not fully sure if I will need some external power supply, I hope that power from cartridge will be enough.

I’m also thinking about making several variants of these boards (dual opl3 chips, 4 channel output), but it depends how much time I will want to spend on reworking projects, how many MMU’s will have to burn, potential costs, how well first versions will work (still I’m not 100% sure what I’m doing :) ) and if there will be any interest at all.

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