Some chars duplicated (w,n) when used ?

miniGranis · Post by **miniGranis** » December 22nd, 2005, 9:26 pm

Hello !

I have a very strange problem with LCDSmartie.
I use this LCD http://www.fractronics.com/2x20oled.shtml
with this wire http://www.fractronics.com/lcdcontrast.gif
This is HD44780 compatible.

LCD works fine except for the following:
Some characters get written two times on my LCD, not all but some.
For instance:
If I type "ww" in a screen LCD shows "www"
If I type "wp" LCD shows "wp"
If I type "Snow" LCD shows "Snoww"

The onscreen display always displays the text correct.

Same behaviour exists for "n" as well.
I have tried several version but problem exists on all versions..

What can be wrong ? Same problem exist if I use a PCI parallel card.

_X7JAY7X_ · Post by **_X7JAY7X_** » December 22nd, 2005, 9:31 pm

Is it only those two chars?

J

miniGranis · Post by **miniGranis** » December 22nd, 2005, 9:37 pm

_X7JAY7X_ wrote:Is it only those two chars?

J

I havent checked all (yet) but sofar Yes, it also seems to happen only if "w" or "n" is the last character. Adding a space after "w" or "n" doesnt make a difference but adding any other character removes the duplicated one.

Code: Select all

Screen def      => LCD output
"abcw"                 "abcww"
"abcw "                "abcww"
"abcwp"               "abcwp"

Do you make any sense of this ?

Edit:
The following characters are suffering from this:
"n","o","v", "w"
An even weirder thing is "z", if I enter "zz" in a screen all is OK
if I enter "zzz" I get "zzzz" one "z" is displayed ok. This thing with "z" is not consistent though.

miniGranis · Post by **miniGranis** » January 2nd, 2006, 10:16 am

No one ?

Post by **limbo** » March 9th, 2006, 11:44 pm

Hello miniGranis
Are you still having problems with the display?

There is no known issue about this problem...
Please check the wirings once more and report any result here..

_X7JAY7X_ · Post by **_X7JAY7X_** » March 10th, 2006, 12:26 am

I would say its a "bouncing" enable line, however it only does it on some characters.

Thats weird.

J

ReverseEngineered · Post by **ReverseEngineered** » March 10th, 2006, 9:17 pm

I would definitely check the wiring. Smartie doesn't actually read the busy flag to determine when the write is done (since reading from a parallel port isn't very portable). If the wires are long, or are very different sizes, timing problems could cause this. Really, the only reason it would ever print two characters is if the enable line was being triggered falsely. This could happen if the voltage is weak (sitting somewhere between high and low), or if there is enough noise to make it look like the enable changed quickly.

Recommend lengths of wire are no more than 6 inches. If you need something longer than that, use a good, shielded extension cable like you would buy from the store. Anything that's unshielded should be less than 6 inches.