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Re: Apple IIc with colour LCD demoed at KansasFest?
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.
-michael
New Applesoft BASIC interface for NadaNet networking!
Home page: http://members.aol.com/MJMahon/