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Author Topic: 16x2 LCD Troubleshooting  (Read 2284 times)
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I spent a while looking through the forums for a solution to the issue I'm having with connecting a 16x2 LCD, but haven't come across anything quite like what I'm seeing. I followed this tutorial for wiring the connections: http://www.ladyada.net/learn/lcd/charlcd.html

I also made the necessary code changes to the LiquidCrystal HelloWorld sketch mentioned toward the end of the tutorial, namely the note about changing this:
Code:
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

to this:
Code:
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

Unfortunately, when I load and run the sketch this is what I see on the LCD:


As far as I can tell, everything is connected correctly. I even double-checked the header pin soldering for connectivity and shorts. The pattern shown on the LCD is at maximum contrast. This pattern was persistent before I connected the data lines (only backlight, pot, logic power connected) and goes away when the pot is turned down. I never got a single line of blocks mentioned in the tutorial at that step. I was thinking that there was something wrong with the LCD, but I tried a 2nd LCD to the same effect.

It would help if a 2nd (or 3rd, or n) set of eyes could look at this and give me some feedback. Thanks!
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What's the exact part number of the LCD?
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http://www.gammon.com.au/electronics

Please post technical questions on the forum - not to me by personal message. Thanks a lot.

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GDM1602K
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Looks OK to me. Try measuring that you have +5V on the pins that should have it.
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Pins 2 and 15 have +5v.
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The wiring and "code" look good to me too. Could be a bad display. Someone asked about this pattern in the past and if I recall correctly he/she sent it back for a replacement. Where was this display purchased?
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I got the display a few years ago from sparkfun.com. I figured it might be the display malfunctioning, so I ordered a 2nd one, different color, same model... similar result. I read that these LCDs are pretty robust, so I'm not so sure it's the display.
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I've purchased from several sources (not including sparkfun) and never had any problems of defective screens, even from surplus stores. I think the other guy with similar problem also bought from sparkfun. Maybe sparkfun got a bad batch.
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Just out of curiosity, what does the display look like without connecting the six red wires to the Arduino ?  Normally you would get 'boxes' on the top row.

Don
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Try the tutorial from Hacktronics.  It worked for me.
Make sure you have the LiquidCrystal.h library loaded
on your computer when you compile the sketch.

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http://www.hacktronics.com/Tutorials/arduino-character-lcd-tutorial.html
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Thanks for everyone's replies! I meant to get back about this earlier. I ordered a new LCD from sparkfun and when I wired it up, everything worked as expected. What are the odds of 2 bad LCDs in a row?
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