Alexander wrote:
"Chris Fonville" schreef in bericht
...
Alexander wrote:
"Chris Fonville" schreef in bericht
...
Alexander wrote:
"Chris Fonville" schreef in bericht
...
This is my first LCD and I am not having much luck. I have checked
over my wiring many many times and cannot seem to find the problem. It
is a 4x20 hd4780 LCD. When I turn it on the backlight comes on and I
receive the test signal, but some lines are missing. The top 4
squares, or I guess pixels, are on but then the next 2 down are not.
The bottom 2 are also on. Here is an example of one character:
*****
*****
*****
*****
*****
This is repeated for each character on the 1st and 3rd line of the LCD.
Is this a bad LCD or do I have my wiring wrong? Also, I can use LCD
Smartie and the LCD will respond but I can only make out some
characters, but most of the screen is gibberish. How can I go about
fixing this problem? Any help will be appreciated. Thanks,
Chris
Chris,
normally you send the ascii code of a character to the LCD (controller),
if this character is displayed on one or more line(s) correctly, you
have initialized and send a succesfully this character. If you only use
the controller's own characters this character is always displayed
correctly, if this character is missing a line (or more) then most
likely the display is broken.
So in your case send one character to all positions, you should see 4*20
of the same character (or one different because of cursor), if not try
another display.
Good luck,
Alex
The example I posted above was just from the test screen. This happens
when the LCD is not connected to the parallel port, but is just receiving
power. If I understand correctly, every other line of the 4 should be
on. This happens with mine, however each character is 8 blocks or pixels
high and only the top 4 are on, 2 are not, then the bottom 2 are on.
This happens all the way across the screen. This is hard to explain in
words, I have uploaded some pictures:
Test screen with and without parallel connection
http://www.chriscomputers.com/lcdtest.jpg
Using LCD Smartie to put "ABC" on all 4 lines
http://www.chriscomptuers.com/lcdabc.jpg
You can sort of make out ABC in lines 2 and 4. Because I can actually
send it commands and it display them somewhat, and because the LCD test
screen is not fully working with just power, I think it is either my
power wiring is wrong or the LCD is defective. Thank you for your help,
Chris
If you connect the first three pins only Vss, Vdd and Vo, the first line
(and perhaps the third line) should be all blocks with the character
width and height.
With only the first 3 pins wired I receive the same test screen, without
the backlight. (http://www.chriscomputers.com/lcdtest.jpg)
Pin 1 - Ground
Pin 2 - +5 volts
Pin 3 - Ground
So I am pretty sure it's a defective LCD. However, is this problem
because of bad wiring on my part, or did I simply receive a bad unit?
Thank you for your help,
Chris
Chris,
That's a good question in my experience (production lin also) there are
always some bad unit's, some with a similar problem.
The problem may also be caused by e.g. ESD or simply by cutting the display
out of the package and damaging the traces of the PCB. Or you might even
have previously connected it wrong.
Because of this problem many retailers don't take any Electronical
Components back, so you're probably out of luck with this one.
Better luck next time,
Alexander
It might have been ESD but I always touch metal before handling any
components and this was no exception. The package was closed with a
string and so I did not damage it when unpacking it. Also, unless my
first wiring was wrong, it was the only way I tried it. I received this
LCD from eBay for $10 + $5 shipping. The seller has refunded my $10 but
I am only out $5. I might try to buy from another seller, but like you
said they all seem to have a no refund, no return policy. I guess I am
lucky to get my $10 back. Any ideas on where I could get a cheap 20x4
backlit LCD from an internet retailer? Thank you for your help,
hopefully if I do get another unit I won't be back here looking for
help! Thanks again,
Chris