DPRG mailing list archives: [DPRG] Dot matix programming problem

Mon Apr 14 17:27:26 CDT 2008

Francesco,    

    Just on a long shot, have you tried a different display matrix chip? There seems to be some sort of latency in the column. The puzzling part is that you are getting a wrap around from what looks like a "9" display from column 4 back to column 0 in your video. Everything else seems to follow the adjacent column so the most likely fault, to me, would be a "leak in the last row of THAT specific chip. I'd say timing but it doesn't seem to be happening on any other row and I would expect to see random dots if it were a simple timing problem. The only other possibility I can see might be that the line from the PIC controlling that row is picking up some stray capacitance and not dropping to a low state fast enough. That would be odd since all the others seem OK. 
   I was recently burned by an IDE Cable with a short and I blamed everything else before I swapped the cable. I could have saved myself a lot of trouble by trying the simple solution first. (I'm not saying I de-soldered everything and started over, but I also won;t say something SIMILAR didn't happen before I discovered the real problem. Sometimes, surplus is surplus for a reason!)

Good Luck
Steve

-----Original Message-----
From: Francesco De Comité <Francesco.De-Comite at univ-lille1.fr>
To: dprglist at dprg.org
Sent: Mon, 14 Apr 2008 3:20 pm
Subject: [DPRG] Dot matix programming problem

Hi, I am looking for some help on a little problem I encounter, while 
trying to program a dot matrix circuit (namely KingBright TA21-11EWA), 
using microchip's PIC18F4620. 

The last dot of a column, if near from a lit pixel, also seems lit. 
What's could be the reason of that ? Any idea ? 

Wiring detail : http://www.flickr.com/photos/fdecomite/2413690327/ 

Little video illustrating the problem : 
http://www.flickr.com/photos/fdecomite/2414510950/ 

Source code : http://users.tvcablenet.be/personal/tvcn28401/dotmatrix.c 

Thanks in advance for your help ! 

Francesco De Comité 

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