> You run the risk of eventually ruining the display by causing
> electrochemical
> action if you don't use AC, although reportedly modern
> displays are cleaner
> inside and less easy to damage than early models.

Hmmm...sounds like a quick and inexpensive way to go for *some* projects...

Seems to be that larger displays can handle higher freq this way..although
this seems counter-intuitive ahen considering the capacitance of the
segment,. Hmmmm...


> Imagine you apply a 50% duty cycle clock to the backplane of
> your static
> display. Apply the same clock to one input of an exclusive OR gate.
> Now if you apply a "0" to the other input, both the backplane and the
> gate output have a 50% duty cycle square wave on them- in phase. If
> you measure between the two points (backplane and gate output - or
> segment driver) you'll get very close to zero volts AC or DC.
> Now apply
> a "1" to the input of the exclusive OR gate. The output of
> the gate will
> still be a square wave of the same frequency, but now OUT of
> phase with the
> backplane. If you measure the voltage between the two points
> you'll get
> very close to 2* Vdd peak-to-peak, with an average voltage of zero (it
> spends half the time at +Vdd and half at -Vdd, so the average
> is zero).

That would be the same sheme that I found here:
http://www.lxdinc.com/AppNotes/BasicsofLCDOperation.htm
> You can think of the LCD segment as being like a small capacitor.

And it's the capacitance that causes the lcd to see AC then, isn't it...?!

Well, I've ordered a few drivers that I found at digi-key in the meanwhile,
also some quad XOR's.
The gates are useful perhaps with single digit use - it would take two quad
gate chips to control one 7 seg digit & decimal pt. Granted they are around
$0.40 each, but the wasted real-estate would be massive for a 4 digit
display.
The driver chips are sounding more promising.
Writing the code to toggle the commons and the segments in opposed phase is
beyond the limits of my available time.....

Thanks all for the great replies on this....The piclist is definitely a good
thing.

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