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40inD
Joined: 30 Jul 2007 Posts: 112 Location: Moscow, Russia
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SAA1064 flickering |
Posted: Tue Apr 22, 2014 1:44 am |
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Problem is when SAA1064 drives 1.8" LED displays at max. current the image has SOMETIMES flicker (or running wave) effect, which is noticeable by naked eye. At minimum current this effect is not appearing.
The other chip on same board which drives 0.8" LEDs does not have such problem.
In both cases timing capacitors are 2.7n, decoupling caps - 0.1u and stabilized power - 5V 1A.
Perhaps, need to try to reduce timing capacity? |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19480
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Posted: Tue Apr 22, 2014 4:36 am |
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Probably your supply is not actually maintaining regulation as the LED's switch. |
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40inD
Joined: 30 Jul 2007 Posts: 112 Location: Moscow, Russia
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Posted: Tue Apr 22, 2014 4:51 am |
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You suggest to add more electrolytic capacitor? |
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oxo
Joined: 13 Nov 2012 Posts: 219 Location: France
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40inD
Joined: 30 Jul 2007 Posts: 112 Location: Moscow, Russia
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Posted: Tue Apr 22, 2014 5:53 am |
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No, in my case I2C works ok, and i don't think that flickering is I2C problem. The second chip on same pcb works fine. And flickering also appears when there is no I2C activity with addressed chip. Also, flickering appears not always but in some very slow period.
It's look like some interference between 2 processes with close frequencies inside the chip. |
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temtronic
Joined: 01 Jul 2010 Posts: 9216 Location: Greensville,Ontario
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Posted: Tue Apr 22, 2014 6:26 am |
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'Old School' power supply rule is to build it 10X greater than the steady state current demands.
So, if your LED draws 150ma( all segments on, worst case) you need a MINIMUM of 150 * 10 = 1,150ma . Be sure to ADD whatever current the PIC and support chips draw as well !! They could easily add another 50 - 150 ma ,so in this case you need 1,150 + 150 = 1,300ma or 1.3 Amps.
hth
jay |
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Mike Walne
Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK
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Posted: Tue Apr 22, 2014 10:56 am |
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It's time to get the 'scope out and make some very careful observations.
Look for power supply drop-out, timing jitter etc.
Mike |
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