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liquid crystal display - why should i use AC?

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ZeleC

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using the cd4543

hello i m using a six digits liquid display
i read that it needs ac power but im using dc and im not having any problems.so why should i AC ???
will the problems appear later althoughits been quite a while since i ve been using it
and can some one give me schematics that uses AC power to control the lcds ,and what drivers should i use . i found one in microchip but it has a serial input as i read (AY0438 familly).
can any body help me

thx guys
 

Hi ZeleC,

if you use a DC voltage to drive your LCD the segments will be destroyed after a while. This is because the crystals are oriented always in one direction (dark) and if you turn off the segment it wont get back to the clear state. If you use AC to darken the segments the crystals can never 'store' an orientation and this problem won't appear. Normally you use a frequency of about 300-1000Hz.
There exist some 7-segment driver chips in the CMOS4000 series that are capable of driving LCD's.

Bye
 

im already using a cd4543 on my board i have used before for led display but i changed to lcds .it s not giving me any problem till now i been using it for two weeks but maybe later it will, so thx to mr_ghz i rewied the cmos4000 familly and found out that this same chip can be used for lcds , but we should apply a square wave form on the ph pin (pin 5). so thx mr_ghz
and guys im still looking for a single chip that controls more than one digit and that can be controlled from a databus (not serial)
thx in advance
 

Is it possible that the AC power is used by the backlight system for the LCD?
 

INTERSIL

ZeleC said:
im already using a cd4543 on my board i have used before for led display but i changed to lcds .it s not giving me any problem till now i been using it for two weeks but maybe later it will, so thx to mr_ghz i rewied the cmos4000 familly and found out that this same chip can be used for lcds , but we should apply a square wave form on the ph pin (pin 5). so thx mr_ghz
and guys im still looking for a single chip that controls more than one digit and that can be controlled from a databus (not serial)
thx in advance[/quo

another kind of chip for same uses is 4556 if you have to drive more display you can used a multiplixer chip 4553, see cmos data sheet for information

if you want to use a singal chip then intersil (ICL) have these kind of chip up to 4 1/2 half digit driver
Click to expand...
 

I READ YOU!!

HI
I'M JUST AT THIS MOMENT DOING THE SAME YOU ARE DOING !!
I DECIDED TO USE A TEXAS MPS340F413 A VERY INEXPENSIVE CHIP
A $2,60 16 BITS CPU WITH LCD DRIVERS BUILT IN
I ALSO GOT ME A LCD DISPLAY FROM LUMEX 4 DIGITS ( YOU CAN USE TWO) FOR $.40 EACH IN VOLUME
SO I HAVE A CPU + LCD SOLUTION FOR $3.00
TRY TO BEAT THAT!!!!!!!!! ..
ON TOP . YOU CAN BUILD THE PROGRAMING/DEBUGGING LPT ADAPTOR FOR $1 AND YOU CAN DOWNLOAD THE DEVELOPMENT
ENVIROMENT ( IDE + C + ASSAMBLER) FOR FREE ( 4k CODE LIMITED)

IS UP TO YOU!
 

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