how to drive led matrix
The LCD drive signal is not simple.
Basically, one of the signals, usually the backplane for the character, is a square wave.
When a pixel is 'off' the signal to it is also a square wave and is in phase. The two signals, although going from 0V to the full drive voltage, are identical so across them nothing can be measured and nothing activates the LCD.
When a pixel is turned 'on' the signal to it is inverted so it is out of phase with the backplane. Now the voltage measured between the backplane and the pixel is reversing on each cycle of the square wave, it is AC. As the backplane goes high, the pixel goes low and vice versa.
You can run LCDs on DC, which is what you need for your LEDs but the electrodes quickly electro-plate to one side, hence using AC.
Although I wouldn't recommend it, you can recover the signals you want by using XOR logic gates. If you put the backplane signal into one input and the pixel drive into the other, the output will be '1' if the pixel is on and '0' if it is off. You need an awful lot of XOR gates though!
A better solution is to emulate the LCD controller in software and use multiplexed drives as suggested earlier.
Brian.