Decode LCD drive?

Subject: Re: Decode LCD drive?

I'm assuming you mean bare glass LCD

amplifiy the signals to logic level (eg using comparators, or transistors) and use backplane signal slightly delayed to drive an edge-triggered latch. (which latches the segment signals) or trigger an interrupt etc..

on.

) and use backplane signal slightly

I did this once for an LED display. I had to build level shifters for one of the two drives (anode vs. cathode) because it wasn't ground referenced a nd didn't swing widely.

For LCD with multiple backplanes this will require reading by an ADC to det ect the various levels. I should be something an MCU can do if it has enou gh ADC inputs since the rates on the LCD are rather slow compared to what t he MCU can do. Whether or not you will need to add more multiplexer inputs depends on the number of segments on your display.

Rick C.

I'll have a go with that and the other suggestion after a more low-tech simpler attempt, because of the multiple (varying?) levels involved. Little bridge rectifiers of 4x epitaxial diodes to each relevant pair of lines, to DC and then opto-isolators if enough drive, because of the floating nature, or buffers of some sort, to get a ground-referenced set of data.

N_Cook wrote

When more complicated is allowed:

Proof of concept, will decode any display. Does take some programming and a fixed setup. Does not void guarantee on whatever you want to decode.

Maybe use 2 LCDs in parallel, one for this methods...

I like this idea a lot better as compared to the brute-force idea of decoding the drive lines directly with a bunch of latches and logic, seems very inelegant and clunky. This is a Zen-solution. Go with the stream, not against...

So far so good , tried 1X4 epitaxial bridge diode , consistent 1.6V for lit segment and 1V for off, good discrimination but floating levels of course. But 120K load the on-voltage DC drops to 1V so opto decouplers are out. For decoding purposes you can ignore the 7-segment d segment to uniquely define the digits 0 to 9, but can you get away with a minimum of 5 segments decoded?

a f b g e c d

I think 'C' is also unneeded for decoding

confirmed. Next is to check a basic differential comparator works, rhwn replicate for each segment. Then hopefully no inter-digit corruption of the drive to the LCD by multiple cross-connected diodes.