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For LCD pixel activation need reverse phase rectangular voltage against backplane (common). Frequency about 20...100Hz. For testing make short all row, and make short all columns. This two terminal can activate all pixels.
The character-LCD module have a driver chip with parallel or serial interface. My test-method works only with "naked" LCD. For testing equal backplane or dot-segment. If You have e.g. a four digit 7segment LCD with one backplane (not independent BP for each digit), this is always the pin1 and/or pin40.
thanks Sebi, i can test a 7 segment lcd now. But could i use the same method in testing a character one? i know a character one has a controller and driver to light up the lcd but is there anyway to test it without the driver and controller?
one more thing. is there any datasheet on the web which is for the "naked" lcd(dot matrix character). Most of them which i have found are the modules which already comes with the driver and controller.
I think today no more existiert the "naked" version of dot matrix LCD.(the driver circuit too complicated with many IC-s and expensive) The modules contains a driver, character generator,some flash for customer definied characters, and parallel or serial interface. In the very old time i've seen a few pieces, but - just thinking about - need one EXOR-gate for each dots for driving or staircase signal generator for multiplex-mode (DC-component of drivig signal not allowed)! So this method is dead.