lcd4linux-users

[lcd4linux] Data pins seem to be shorted on HD44780

[Aaron K. <aar...@ro...>]

FIrst off here is my LCD info:
it is a HD44780 (or compatible) 20x4 backlight display from:
http://cgi.ebay.ca/HD44780-characte...QcmdZ ViewItem
(just as a not mine is a little different then the photo there. THey
have 5 circut things/blackblobs where as mine has three)
as for the type of backlight i presume LED as that is what the auction
says and this is not a thin lcd.

Basically the problem is that all the data pins seem shorted...sort of.
I get the the test screen okay when i connect the power. But if i don't
connect the power and just have the parallel port connected and the
backlight turned on (i put a swtich in) the backlight kinda flashes.
What i eventually figure out is that somehow and signal being sent along
the data pins is being sent to the 5+ pin for the controller which
shares a [ath with the backlight so it causes the backlight to flash. As
well there is a non-inf resistance between the data pins and the +5v pin
(about 3 k one way (with +data pin and -the 5+ pin) and 20k the other
way)
i have check a few things.
Could not find any shorts
that resistance value is still there without the wires connected
placing a diode did not help (trying anyhting i could think of and i did
not think it would work either)

SO is this some internal flaw on my lcd or something else?

THanks

Re: [lcd4linux] Data pins seem to be shorted on HD44780

[Michael R. <re...@eu...>]

Hi Aaron,

> FIrst off here is my LCD info:
> it is a HD44780 (or compatible) 20x4 backlight display from:
> http://cgi.ebay.ca/HD44780-characte...QcmdZ ViewItem
This link does not work...

> Basically the problem is that all the data pins seem shorted...sort of.
> I get the the test screen okay when i connect the power. But if i don't
> connect the power and just have the parallel port connected and the
> backlight turned on (i put a swtich in) the backlight kinda flashes.
> What i eventually figure out is that somehow and signal being sent along
> the data pins is being sent to the 5+ pin for the controller which
> shares a [ath with the backlight so it causes the backlight to flash. As
> well there is a non-inf resistance between the data pins and the +5v pin
> (about 3 k one way (with +data pin and -the 5+ pin) and 20k the other
> way)

The resistance look fine to me. As for the flashing backlight... I've
never tried it this way.

Are you sure you're using the correct wiring? I've seen displays where
the pins are not 1-2-3..14-15-16, but 15-16-1-2-3...13-14!

What do you mean by "test screen"? alternating black/white bars? Then
the display should be ok, and it means that your contrast voltage is in
a reasonable range (don't ask how much hours I've spent looking for
bugs, when everything was fine, but due to wrong contrast settings I was
unable to see the display running correctly :-) (Sam, are you listening?
SCNR)

What happens if you connect everything and run lcd4linux?


bye, Michael

-- 
Michael Reinelt <re...@eu...>
http://home.pages.at/reinelt
GPG-Key 0xDF13BA50
ICQ #288386781