This is likely to be a fair challenge, since the C64 cassette deck is not an audio deck. I don’t recall the details of its circuitry off-hand, but but they used some tricks to make it a lot simpler than a standard audio deck.
You can build one for under $15. The most expensive part is the ATmega1284P MCU, which can be had for less than $8; the rest is an SD card to SPI adapter (a buck for one that includes a 3.3V regulator and level conversion) and some discrete parts. I don’t have full details right to hand, but this blog entry and this one may help.
Note that older versions of the SD2IEC used an ATmega644; this has only half the flash memory and so not enough room for the very latest firmware images.
I’ve got a couple of friends using it and it works quite well. I’ll no doubt be building one myself whenever I get back to using my C64 again.
While apparently not a preferred option for @IsaacKuo, this video on assembly, setup and operations (on DOS, using Star Commander) of the XA1451 serial to parallel port floppy adapter is somewhat complementary to this thread. (What this does is allowing you to directly access a C64 drive for read and write under DOS or similarly under Linux.) The video description also includes some useful related links, like to https://sta.c64.org/xa1541.html.
PS: Have a look at the comments, as well, regarding a few hiccups occurring in the video.
Just in case anybody wants to chase this down, I now suspect that the Commodore deck is using saturation recording, which is well described in that link. It’s very cheap, very cool, and in no way audio.
And (me being grumpy here) what’s up with all these guys calling things like the XM1541 a “cable?” Since when do “cables” have entire CPUs, 16 KB of RAM, etc.in them?
Thanks again for the info and suggestions! At this point, I’m going to bite the bullet and import an SD2IEC. Things are a bit … hectic. So I can’t really experiment around, and I have fewer spare computers to muck around with since I’m devoting two of them to work-from-home. What might have been my “experimenting around” space is instead my work-from-home space.
So, a simple little compact device directly attached to my C128 is looking a whole lot better, even if I have to spend a little bit of money for it.
My C128 setup is essentially unchanged in the last months - nothing more than a C128 attached to a 1702 monitor. My 1541 drives are in a closet right now. The kids love making PETSCII art on it, and are amused by simple BASIC programs I type on the fly to make PETSCII animations.
A simple little SD2IEC will let me introduce them to “real” C64 games and stuff easily enough.
