Re: Apple IIc with colour LCD demoed at KansasFest?

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

Bill Garber wrote:
> "Michael J. Mahon" <mjmahon@aol.com> wrote in message NK2dnUuhDPJvWIXfRVn-gQ@comcast.com">news:NK2dnUuhDPJvWIXfRVn-gQ@comcast.com...
> : Bill Garber wrote:
> : > "David Wilson" <david@uow.edu.au> wrote in message news:42182773$1@news.uow.edu.au...
> : > : "Michael J. Mahon" <mjmahon@aol.com> writes:
> : > : >I don't know (offhand) how much an external device is permitted
> : > : >to draw from the video expansion connector, or what voltages are
> : > : >provided.  Since it sags with floppy access, I'm guessing that
> : > : >it's the +12v line (used by the floppy motor).  The permissible
> : > : >current drain would have to be at least as large as what the
> : > : >LCD requires or it's a bad idea to use it.
> : > :
> : > : Good guess. According to the Apple IIc Technical Reference Manual
> : > : pin 8 is 12 volts (regulated) and can supply up to 300mA.
> : >
> : > As I had stated previously, there is a fix, and someone
> : > was supposedly going to give me info on how to pull that
> : > up so I could use that supply and still keep a steady
> : > screen display during floppy accesses. I wish they'd
> : > read these posts and fill me in.   :o)
> :
> : I don't know who offered a fix, but I can suggest some limits
> : on what can be done easily.
> :
> : If the LCD you want to use requires 12 volts (and can work
> : within the 300ma limit), then it is not so simple.  You would
> : need a "boost" switching supply to recover a stable +12v from
> : the sagging one present in the //c.
> :
> : If, on the other hand, your LCD can work with 10.5 volts or
> : less, at 300ma or less, then a very simple voltage regulator
> : circuit (one LM340 and a couple of resistors and capacitors,
> : at worst) can do the job.
> :
> : If your LCD requires less than 12v (say, 6v) and more than
> : 300ma (say, 450ma), then a "buck" switching converter can do
> : the job.
> :
> : Both switching converter solutions are more complex than the
> : simple regulator solution.
>
> Heh Heh, it's not even an LCD. It's a 12v monitor that was
> used primarily in Ultrasound systems before the advent of
> inexpensive LCDs, which they use now, most of the time.
>
> There is a picture of this monitor on my web site at:
>
> http://garberstreet.netfirms.com/JPG/DR6509.jpg

Hmm. In that case, I imagine that it uses at least 600ma,
and therefore draws well beyond the video port limit.

If you add its drain to the drain of the disk drive motor,
it's probably overloading the +12v supply and causing it
to sag a volt or more!

Your best bet is to use an external 12v supply, of at least
1 amp capacity.

-michael

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Home page:  http://members.aol.com/MJMahon/