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[DPRG] Driverless LCDs

Subject: [DPRG] Driverless LCDs
From: Mike McCarty jmccarty at ssd.usa.alcatel.com
Date: Fri May 26 16:50:40 CDT 2000

On Fri, 26 May 2000, Patrick Innes wrote:

> Hello, all!  Another question for the list:
> 
> I recently acquired a couple of bare-bones LCD
> displays (no driver electronics), and would like to
> find some information on how to drive them.  

[snip]

> I'm wondering if properly driving them is simply a
> question of supplying power/no power to the correct
> pins, or is there some other secret I should know
> first?

There are several secrets you need to know, if you truly have raw
displays. One of them is that they should *not* be run off of DC
levels. They need AC drive. Driving them off DC eventually causes a
permanent change, due to ion poisoning. A common way to derive the AC
drive is to connect them between gates which can invert the signal.
Like this:


                        +-----+
        Signal o--------|     |      +------------+
                        | XOR +------|Display Cell|--+
        AC     o---+----|     |      +------------+  |
                   |    +-----+                      |
                   |                                 |
                   +---------------------------------+

The signal marked AC is of course logic levels for the system, going
>from 0V to say 5V, not below 0V. Also, normally, the output of the XOR
and the AC both go through buffers, which may be either inverting or
non-inverting.

Mike



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