I have bought a cheap radio controlled clock, and I want to make a hack that replaces the existing LCD display with 7-segment LED's. With my voltmeter in AC mode, I can measure voltages(with respect to battery minus) on the connectors to the LCD of 0.4V(presumably off) 1.4-1.6V(presumably on). I do not know the waveform or frequency of this voltage, but I suppose I can measure it, if I find an oscilloscope somewhere.
How do I convert this AC to a logic signal, that can be used to drive the 7-segment? Is there any standard regarding LCD drive voltages? Does there exist a single drive chip for this purpose? Do I need transistors, op-amps or a chip to make enough current?
UPDATE: There is absolutely no logic in the display itself - it is just a glass plate(with liquid crystal). I can even make the display turn on shortly with dc. All the connector seen on the picture drives the display directly.
Update (Wikipedia LCD) says:
Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field). Displays for a small number of individual digits and/or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment.