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[Lcdproc] HD44780 40x4 with Backlight and winamp wiring

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  • From: sascha.zielinski at (Sascha)
  • Subject: [Lcdproc] HD44780 40x4 with Backlight and winamp wiring
  • Date: Thu, 22 Jan 2009 21:16:27 +0100

Am Donnerstag 22 Januar 2009 20:24:31 schrieben Sie:
> Ethan Dicks wrote:
> > On Thu, Jan 22, 2009 at 12:23 PM, Sascha <sascha.zielinski at>
> > wrote:
> >> Hi,
> >>
> >> I bought a 40x4 LCD with LED Backlight...
> >>
> >> The Documentation describes to connect the Backlight pin through the
> >> BC327 Transistor to Pin 17 of the Printer Port.
> >
> > Yes. That is the "standard" way to hook up a backlight.
> >
> >> Should I then connect the EN2 to GND?
> >
> > If you do that, then you will only be able to use half of your display.
> >
> > The "problem" is that there aren't enough pins for an 8-bit interface,
> > plus 2xHD44780 (EN1 + EN2), *plus* backlight. AFAIK, all 40x4
> > displays are implemented as two HD44780s with all pins tied together
> > except enables. This is because there isn't enough onboard RAM (or
> > column/row drivers, too?) to handle 160 on-screen chars with a regular
> > HD44780, and I don't think anyone extended the chip that way - it's
> > easy enough to add a second controller chip to the back of the LCD,
> > and there's plenty of room.
> It is not only RAM. The display controller has to address each pixel by
> a row and column line. There would be just too many lines for a single
> chip. Additionally there are limitation regarding the current flowing
> through the chip.
> On displays like 40x4 you will not only find two controllers but also
> some extension driver chips which are conntected through an internal
> interface to the controller.
> >> I use Debian Unstable/Experimental. The Version 0.5.2 compiles fine and
> >> runs now for about a day without a problem. I tried also the the version
> >> from cvs server (checked out on 01.22.09 at 5.00 pm CET). If I start
> >> LCDd with my LCDd.conf from stable version, the Lines 3+4 stays blank.
> >
> > If you read C, you could try browsing the hd44780*.c code and see if
> > there were any changes made since 0.5.2-stable that might come into
> > play. I'm wondering how long tying two displays into one virtual
> > screen has been around, or if perhaps the default line for EN2 may
> > have changed in the past couple of years.
> It is true that you cannot have a switchable backlight and a multi
> controller display like a 40x4. As there has been no change between
> 0.5.2 and HEAD regarding this, something other must be wrong.
> If you do like to have both you could just change the one or two lines
> of code, but you will have to keep track of this change.
> > I don't know that lots of the people on this list have 40x4 displays,
> > but perhaps someone with a parallel-attached LCD can comment. I
> > mostly work from laptops now, and few laptops provide parallel ports
> > anymore. Even serial ports are getting scarce. :-( I'm doing more
> > and more work with USB-attached displays even though I miss the
> > directness of driving ones own I/O ports without an intervening
> > software layer to debug.
> I have one 40x4 I use with lcd2usb, but I currently don't have a spare
> connector to hook it up to the parallel port directly. I may give it a
> try this weekend.
> Regards
> Markus

Thanks for the fast replies. I've tried to switch the Backlight menu Option
and off. If the Backlight in Menu is on, I am getting the same behavior as in
the cvs version. So I think setting Pin 17 to High/Low. This is why The LCD
thinks there is no 2nd controller anymore. Is The Backlight Menu Option on by
default in CVS? And how could I change / reset the settings in the menu?

I tried changing the Menu Backlight option by using the joy driver. But I
wasn't able to disable / enable this option I think.

Sascha Zielinski

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