As I recall, you need to invert the wave that you're putting in through the
common terminal, and use THAT to drive the segments.

-Randy Glenn
PICxpertANTISPAM@techie.com (remove ANTISPAM)
http://i.am/PICxpert

"My Finder has died of fits, chokin',
My Finder has quite ceased to be.
OS X's new Finder looks broken,
Please bring back my Finder to me!" - A concerned Mac user

-----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: [PICLIST] [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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