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swap lcd 16x2 with 20x2
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swap lcd 16x2 with 20x2

by kzeoprf on Thu Sep 01, 2011 3:13 am

Hi I am new in this forum, and I want to ask a question concerning the swapping of the two lcds. It seems in this forum there is great experiance in LCDs. Is it possible without changing nothing (swap lcd 16x2 with 20x2)? I have a situation where the 16x2 (lcd1602 blue backlight) is working ok but when I use the 20x2(rt2002a2 blu backlight) it does not. If I connect all the pins on the 20x2 I get in the the straight line but in very week black color. No messages -data. If I disconect RW or/and EN then I get the straight line white OK but no messages. I use starnded hook up wire to connect the LCD with the PIC. Do you have any clue what to do. The fact is that I have a delevirable and last moment I have to use biger display and it does not work.
Any help is welcome. Is there any chance the LCD to be out of order? I am waiting for a new one.
kzeoprf
 
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Re: swap lcd 16x2 with 20x2

by richms on Thu Sep 01, 2011 7:42 am

Some LCD's need a negative voltage for the contrast pin, I have a large one that I got for a PC ages ago that would just show something slight onscreen before initing, but once configuring it properly was as good as blank except from certain angles, took about -1.2v on the contrast pin to get it showing well.

Was something to do with it being an extended temperature range one. In anycase, I just grabbed the negative voltage from the ATX connector for one side of the pot and it worked, till upgrading PSU to one that lacked the -5v rail ;)

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Re: swap lcd 16x2 with 20x2

by meseta on Thu Sep 01, 2011 6:12 pm

Do you know what the chipset on these are? Are they both HD44780s? And are you running the recommended initialisation sequence?

I've had two LCDs before that behaved differently on startup, one of them works without initialisation, the other one requires the initialisation sequence (could have been different chipsets).

But besides that, as richms mentions, try adjusting the contrast on the contrast pin. (Though try the positive voltages before doing into negatives first).
meseta
 
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Re: swap lcd 16x2 with 20x2

by kzeoprf on Fri Sep 02, 2011 12:01 pm

It was chosen to have the same controller and the same sequence.
16x2/ http://www.ic-on-line.cn/download.php?i ... &file=0053\lcd1602a_398762.pdf
20x2/ http://www.electronikdreamz.com/data/LC ... 0_20x2.pdf
kzeoprf
 
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Re: swap lcd 16x2 with 20x2

by liudr on Fri Sep 16, 2011 10:45 am

Is it possible that you took pin 16 and thought it was pin 1? If you completely reverse all the pins 1-16, 2-15, etc. it is possible that you will still see back light on and power on and blocks. When you turn potentiometer, do you see contrast change? Are you sure the contrast setting of thie 20x2 is identical to the 16x2?

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