calc/watch LCDs

[csb]

Hi,
I'm currently building a PIC-based frequency counter, that needs 4 or 5
7-segment led displays. But I already have a bunch of recycled 8-digit
calculator LCDs. To re-use them, I suppose it would only be a question of
pinout/voltage? but that's precisely my question. There not
marked/branded. Has anyone reverse-engineered LCD pinouts? Perhaps
monitoring voltage across pins while the calculator is on?

Thanks for any help,
csb

 

[Wolfgang Mahringer]

Dear csb,

csb wrote:

I'm currently building a PIC-based frequency counter, that needs 4 or
5 7-segment led displays. But I already have a bunch of recycled 8-digit
calculator LCDs. To re-use them, I suppose it would only be a question
of pinout/voltage? but that's precisely my question. There not
marked/branded. Has anyone reverse-engineered LCD pinouts? Perhaps
monitoring voltage across pins while the calculator is on?

I suppose these LCDs are not dot matrix type.
You can try using a polarizing filter (e.g. from a photo camera) to make
the traces in the display visible.

To save pins, calulator displays are often "triplexed".
I don't see a way of triplexing an LCD with out extra logic on a PIC.
Standard LCD display (as these from LCD multimeters, 3 1/2 digits e.g.)
can be driven directly with only litte logic.

HTH
Wolf


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[Lewin A.R.W. Edwards]

7-segment led displays. But I already have a bunch of recycled 8-digit
calculator LCDs. To re-use them, I suppose it would only be a question of
pinout/voltage? but that's precisely my question. There not

There's a bit more to it than that, but you can probably see the
pinout (at least for the segment lines) by looking at the right angle.
Put a 1.5V supply on one pin and run the other line of the supply down
the rest of the connector, see what lights up. Rinse and repeat