I've been working on a uart-to-cassette interface[1] for my
simple z80 SBC for some time now. The design (which is in
the notes at the link below) was simple, but I could not get
it to work "out of the box." I got some help on an electronics
forum, and it worked with a loopback setup. I think I may have
already mentioned all of that in my phlog somewhere...
In any case, it worked, but when I tried to record the output
on my Sony ICD-PX312 audio recorder, and play it back into
the circuit, the levels were just too low. After a few tries,
I'm happy to report that I was able to find and build an
LM386-based amplifier, to get that signal up to the level I
needed. The original text now comes back through and is
converted properly.
Next, I'll get the whole thing integrated with my z80
computer, using a 7408 AND gate (per some help from bboard
folks over at SDF). It's going right between the max232
IC and the 68B50, so it can essentially save/load whatever
is typed through the serial interface. This isn't at all
how a vintage computer of this type would do it, but since
I don't know much assembly, I'm opting for something easy.
Basically, you'll get your program typed in, type out the
command "LIST" and then start your recorder. Hit enter, and
as your programs lists, it will be saved as audio to your
recorder. When you want to load it again, you simply get
your Basic ready to take lines and hit play. This all
happens at 300 baud (I have a hardware clock switch on
my sbc so I can live switch the clock on the 68B50 between
115200 and 300 baud. tested and working.)
I realize this is not that exciting in general, but I've
been working, and learning, on this schematic since the
beginning of Dec17, and planning it since Oct17. I didn't
know a thing about 555's, LM358's and LM386's before I
started, and now I've learned a ton. It's a fun hobby,
for sure.
[1]
gopher://grex.org:70/1/~tfurrows/projects/uart_cassette/
