This might work. The Maxim data sheets specify minimum +/- 5v output, I
just measured the output not under load, and it was about +/- 5.93v
The negative side would need no regulator because of the contrast control
(and I think it can handle, in theory, up to about -10v) and a low-power
regulator on the + side. 78L05?
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On Tue, 14 Mar 2000, Micah Dowty wrote:
> On Tue, 14 Mar 2000, Geoffrey Wossum wrote:
> > > Another suggestion: use a charge pump to generate the +/- 5v. You
> > > probably have a Maxim MAX232 for your serial connection anyway, right?
> > > It has *two* buffers - use one for serial, the other for the LCD.
> > MAX232 gives +/- 10V outputs in my experience. Probably less on 3.3V
> > supply, if it would even run on 3.3 for you. You could regulate the
> > output down to 5V I suppose.
> > Big problem is I don't think MAX232 (or anything else in the family) would
> > let you draw much current off of it. They're rated for around 850mW of
> > power dissipation, which is 170mA @ 5V. Don't know if that's enough for
> > an LCD. Or if it's a good idea to be pulling current off of it.
> A while ago, when I was into Basic Stamp stuff, I had tried powering a
> mouse using a MAX232. They can't handle very much current. The MAX3241
> I'm using is designed for 3.3v, has 3 transmitters, and 5 receivers.
> It was designed for laptop computers, and Maxim guarantees that it can
> drive a mouse. Mice generally use about 10ma, which is similar to what
> an LCD needs. The voltages it produces are available on the charge pump's
> capacitors, so it wouldn't require devoting 2 transmitters to it. It's a
> good idea. I will have to test the stability of the voltages it produces.
> The negative supply can vary, because it goes through the contrast PWM
> anyway, but my LCD has been fairly picky about its 5v supply. That might
> work, and if it does it would save about $6, and of course reduce
> complexity. Also, turning off the LCD would be as simple as turning off
> the serial port.
> > ---
> > Geoffrey Wossum
> > email@example.com
> > Project AKO - http://rover1.uta.edu/~ako
> > Internet Imperialists - http://inetimperial.sourceforge.net
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> Micah Dowty
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