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musti463
Joined: 19 Sep 2013 Posts: 66
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GLCD Contrast Fluctuation ! |
Posted: Tue Dec 23, 2014 11:56 am |
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I am using 240x128 GLCD with T6963C. when i am run the code glcd contrast has fluctuation. Why? Problem is the hardware or software? _________________ M.Emir SADE |
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temtronic
Joined: 01 Jul 2010 Posts: 9246 Location: Greensville,Ontario
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Posted: Tue Dec 23, 2014 12:28 pm |
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'contrast' problems generally indicate a weak power supply...
possible causes include
1) minimal power supply
2) insufficient decoupling
3) excessive current demand
4) EMI/noise
Without knowing what your hardware is, I'd guess #1. I generally use a 5V 2 Amp 'switching wallwart' style supply for 99% of my projects, add 100mfd and .1 caps on the PCBs and do not have any LCD issues.
hth
jay |
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musti463
Joined: 19 Sep 2013 Posts: 66
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dyeatman
Joined: 06 Sep 2003 Posts: 1934 Location: Norman, OK
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Posted: Wed Dec 24, 2014 6:52 am |
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... _________________ Google and Forum Search are some of your best tools!!!!
Last edited by dyeatman on Wed Dec 24, 2014 10:35 am; edited 2 times in total |
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temtronic
Joined: 01 Jul 2010 Posts: 9246 Location: Greensville,Ontario
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Posted: Wed Dec 24, 2014 8:08 am |
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Ok, had a look at the pngs....
Just where does Vee for the display get wired to ? You have the contrast pot getting power from 'Vee' of the GLCD connector. Does that LCD SUPPLY poewr to that pin? It's not usual for an LCD to supply power.
I suspect it needs to be connected to a power source. If you post a link to the display you're using, that will help.
having 3 switching power supplies on the PCB doesn't help ! Using linear regulators would really quiet down the EMI, be simpler to assemble,cheaper too !
also, traces seem very,very thin to me.I prefer 'thick/wide' traces and big donuts.make for more reliable/robust PCB.
hth
jay |
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musti463
Joined: 19 Sep 2013 Posts: 66
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gaugeguy
Joined: 05 Apr 2011 Posts: 303
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Posted: Wed Dec 24, 2014 9:01 am |
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That is the forward voltage drop of the backlight LED, not the supply voltage. You should be using either a current limited supply or a higher voltage with a dropping resistor to limit the current. |
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temtronic
Joined: 01 Jul 2010 Posts: 9246 Location: Greensville,Ontario
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Posted: Wed Dec 24, 2014 9:24 am |
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What's the voltage going to pin 4, VO of the LCD display ?
Also, voltage at VDD of the display ?
jay |
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Jerson
Joined: 31 Jul 2009 Posts: 125 Location: Bombay, India
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Posted: Wed Dec 24, 2014 9:56 am |
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I am making an experienced guess that the 12V power supply is not rated for adequate current supply to the circuit. So, as the GLCD gets written to/there is activity, you are getting contrast flicker.
The easy way to confirm this theory is to halt your code execution using a while(1); statement after writing some data to the GLCD. No/reduced flicker should be there in this case.
As for the V0 etc, it seems okay to me. I have used similar GLCDs based around the KS0108 driver chipset. |
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