Re: Poor-man's Catweasel

["Michael J. Mahon" <mjmahon@aol.com>]

mwillegal wrote:
> Hi Michael,
>
> Yeah, I thought about driving the 5 Volt regulator from regulated 12
> Volts, but I figured that would put extra load on the 12 Volt
> regulator.  At some point, when I get time, I've got to measure
> current and see if I need to make any changes.  I know that
> accidentally inverting the level of the stepper motor controls didn't
> help with the 5 volt supply, so the heat issue may already have been
> solved. I haven't thought about checking it after making that fix.  So
> far, after many hours of operation, the power supply hasn't given any
> sign of trouble.

The stepper phases and the drive motor are both powered by +12v, so
the +5v was not significantly affected by the phase inversion.  On the
other hand, that placed a significant load on the 12v, by increasing
the current, and especially the duty cycle, of the phase windings.
(I'll bet the stepper motor got pretty hot, too.)

I'd estimate the total +5v current requirement at under 100ma, while
the +12v must supply well over an amp during stepping and motor start
and run.  You'll probably see more current consumption while the head
is on the outer tracks of a diskette than when it's on the inner tracks,
and individual diskettes will cause quite a variation.

> I also thought about looking for a inexpensive switcher with the right
> voltages.  I was even contemplating using a spare Apple II supply for
> initial debug.  12 Volt wall warts are everywhere, dirt cheap and
> don't take up much space.  In the end, adding a few power supply
> components to the board really took less effort than messing around
> with finding the right switcher and figuring out how to mount it.

I can see that--particularly if heat is not an issue.

> This is definitely intended for a box.  Size and shape will probably
> be driven by finding the best way to expose the 20 pin Disk II header
> from a standard enclosure.

Yep--that's fun...  I've found the "boxed" male connector a good way
to bring the connector out in the open.  In this case (!), I guess
you'll want a right-angle version.

> Regards,
> Mike Willegal
>
> On Feb 6, 4:49 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> > mwillegal wrote:
> > > I'm pretty far along on a "smart" version for DIsk ][ drives,
> > > formatted in DOS 3.3 format.
> > > http://www.willegal.net/appleii/appleii-disk-int.htm.
> > BTW, you can cool down your +5v regulator by running it from
> > the *regulated* +12v instead of the unregulated.
> >
> > A small switching supply that outputs +12 and +5, and maybe
> > even -12 and -5 (though that's less important), is probably
> > available surplus for under $10.  (When I tried this--without
> > the microcontroller, hoping the parallel port would work--
> > I used a "brick on a rope" that supplied +12, +5, and -12.)
> >
> > (I'm assuming that eventually this will all go into a box
> > anyway.)

-michael

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