Direct LCD drive with a PIC is real easy.
Attached one output pin to the LCD common. Drive the LCD segment inputs
with more PIC outputs. Setup an interrupt to run at about 50 hz. At each
interrupt
switch (invert) the common state and the segment states.
Make the segments you want on, the opposite of the common state.
The segments you don't want on, make them the same as the common state.
This will give you AC across all the LCD segments, lighting the ones you
want.

For 2:1 or 3:1 multiplexing put a resistor divider across the commons. For a
high,
drive it high, for a low, drive low, for a mid voltage (2.5 typ), make the
pin
an input.

With a 16C62 and 22 I/O's, you can direct drive a 3:1 mux LCD with up to 57
segments!

Jason Wolfson

___________________________________________
 Lipidex Corp
  50 Franklin Terrace
    Duxbury MA 02332
          781-834-1600
              781-834-1601 FAX
                      jason@lipidex.com
____________________________________________

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Lea
> Sent: Monday, June 05, 2000 12:03 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC] How to control a dumb LCD
>
>
> Hi People of the list
>
> I'm trying to control an LCD 3 1/2 digit display, this one has no
> controller,
> the main reason for use this, is the cost, about 3$ each.
> the data sheets says that it works with 30 - 150 Hz AC 5V ps, so I build
> an small oscilator and test the display, all Ok, It works, but how can I
> control it with the pic without a dedicated chip 4 it.
> If I connect the oscilator to the common lcd pin and all the
> segments to a PIC, all segments will lite on, doesn't matter if the ouputs
> are high or low because it is AC.
> So, the question is: It's possible to turn on/off the segments setting the
> tris registers???, so if the pin is input the segment should turn off.
> I don't know if the small leakeage of the pic's input is enough to turn on
> the LCD segment because they need almost no current to lite on.
>
> Also I was reading, (don't remember where) that an intermediate voltage
> on a pic's digital input will cause an increment of the pic current. is it
> true?, if almost all ports are connected to the LCD, it will be
> dangerous to
> turn all as inputs?.
>
> I know that what I am trying to do is quite weird but if it works will be
> nice :-).
>
> Thanks.
>    Leandro J. Laporta (LU2AOQ)     mail: lu2aoq@yahoo.com
>  wrk: Arg. Assoc. for Space Tech.   ham: TCP/IP high speed group HSG
>
>
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