18 Nov
2009
18 Nov
'09
8 p.m.
Be warned that I don't even own a PC with audio recording facilities, and
still use real cassettes for this sort of thing. But I can suggest some
things to try..
I'm working on a Tomy Tutor tape decoder because, well, no one else is. To
that end, this weekend I managed to crack the encoding and now have a
primitive tape decoder that reads an AIFF audio file and spits out bits for
a higher-level decoder to process. To date I can now see the bit pattern for
the GRAPHIC paintbox, and can even do rudimentary decoding of BASIC programs.
So far so good.
OK, I think we can assume you've got valid data onto the PC/Mac.
However, playing back that exact uncompressed 44.1kHz 16-bit mono AIFF into
the Tutor doesn't work (before you ask, the Tutor's tape inputs are mono).
The Tutor doesn't see the sync mark, and never loads the "tape." I
recorded
this a few times, making sure that all the output got on the audio file,
and no dice. I also played with line levels and varied the output volume
level through all the fine steps the Mac would let me step, and the Tutor
just sits there.
What I would doo is grab the 'scope. Try loading a program from a real
cassette and see what the signal looks like _inside the Tutor, on the
input socket_. If you can get to the output of the digitising circuitry
(often just a comparator) -- it's not hidding inside an ASIC -- look at
that too.
Then try 'playing' the signal from the PC/Mac into the Tutor. First check
there's actually a signal getting throuigh the input socket (I've lost
cound of the number of times I've had a mis-wired cable, or when a mix-up
of stereo and mono jack plugs ('phone plugs' to you) has shorted out the
signal). See if the signal is about the same amplitude. Make sure there's
no mais-freqeuncy (50Hz, 60Hz, 100Hz,120Hz) ripple on it. If you can
check the ouutput of the comparator stage, does that look much the same?
-tony