14 Dec
2007
14 Dec
'07
10:55 a.m.
...don't you also need to *write* at the same speed? I'll bet
there's something in the design of the audio cassette heads that
makes it hard to do that.
I'm pretty firmly in the camp of (at least initially) abusing
technology by changing as few parameters as possible. That'd mean try
the experiment with a (or 8, but since it's a serial computer .... )
head mounted over a drum (or disc) that pulls tape past it at the
design speed for that head, 1 7/8 ips (?) for a cassette tape head.
That also implies the max. data rate will be something like the max.
bandwidth of the tape recorder, maybe 10 kHz. (Hey! Stereo recorders
will give you 2 bits parallel, at close to 18 kHz....)
Once you get it running at that clock rate and get the
distributed.net client compiled and running ( :-) ), then work on
speeding it up. I'd say the kewl factor on that machine will so blow
away anything I've ever done that you need not also have a MHz
advantage... Good luck!
At 9:43 -0600 12/14/07, cctalk-request at classiccmp.org wrote:
--
- Mark, 210-379-4635
-----------------------------------------------------------------------
Large Asteroids headed toward planets
inhabited by beings that don't have
technology adequate to stop them:
Think of it as Evolution in Fast-Forward.
Very
interesting project. Won't standard tape heads only work reliably if
the magnetic material's passing by at quite a narrow range of speeds,
though? Google suggests that's 1 7/8" per second, which isn't very fast at
all - a drum that can do a few tens of RPM seems possible, but 6000??
I don't think it makes a difference. The higher the speed, the larger the
voltage from the flux transition, but that shouldn't be a problem (within
reason). The head gap and medium speed dictates the "resolution" of the
system. You can think of it as being like trying to write with different
sizes of pen nib.
Look at reel-to-reel audio recorders - they may run at a variety of speeds,
giving a tradeoff between audio quality and recording time. You can use a
higher flux density with a larger head gap (and a correspondingly larger
drive signal), but you need to haul the tape through faster to maintain the
bandwidth.
On playback, you get the problem that higher frequencies produce a higher
voltage, hence the need for equalisation (not unlike the RIAA curve for
magnetic record pickups).
In this case you probably just want to detect the presence or absence (or
possibly polarity) of a pulse. Equalisation won't be a worry.