Recently, I've been fascinated with LCDs and how to drive them from a microcontroller. They're not simple like LEDs, you have to give them an AC signal. If you drive them with a DC signal, it will destroy the LCD.
So I read a bunch of pages about driving LCDs searching google on "driving lcd microcontroller".
In the pdf at http://www.atmel.com/Images/doc2569.pdf it describes how you can make the necessary voltages to swing from -vlcd to +vlcd using waveforms that runs from 0 to +vlcd and are out of phase with one another.
This totally baffled me, how could you make the negative voltage differences with only positive voltage?
I was stumped before I realized that the negative voltage difference wasn't from COM to ground or SEG to ground but instead from COM to SEG.
When COM is +vlcd and SEG is 0, you get +vlcd across COM-SEG.
When COM is 0 and SEG is +vlcd you get -vlcd across COM-SEG.
This page was pretty helpful to see this:
http://www.arduinoos.com/2014/08/lcd-direct-driving/
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