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Color bleeding — Parallax Forums

Color bleeding

James NewmanJames Newman Posts: 133
edited 2008-01-21 07:31 in Propeller 1
Hey guys,
I'm trying to finish up a motion control project I've been working on. I'm using the standard VGA-Text module for output, and have started to mix a palette up that will be suitable. I've noticed I have alot of color bleeding going on. I'm not sure if it's intensity or what, but I noticed that %%200 on %%000 looks great... if your in to red... it doesn't seem to bleed at all. Does anyone else have any color bleeding going on? Would adjusting some sync values help this any? This is on the proto-board, and soldering the vga/ps2 connector was my first soldering job, could a bad connection cause excessive bleeding?

Thanks for any help. I searched the forum (search.parallax) and either came up nothing usefull, or spammed pages of 'bleeding edge'...

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-01-14 03:55
    If red on black looks okay, and if you think it might be a bad connection, try green on black and blue on black. This will isolate the problem to one or two connections. If that doesn't help, try a different monitor and a different cable to make sure neither of those is contributing to the problem.

    -Phil
  • cgraceycgracey Posts: 14,239
    edited 2008-01-14 04:35
    Be sure that you've got really good decoupling capacitance on VDD/VSS. A 1uF ceramic cap right on the power pins can be critically important. The problem is that a noisy power supply will increase PLL jitter that will cause time-smearing of video data. Also, some LCD monitors have better/worse internal PLL's than others (which are used to INPUT the video signal). A good old CRT monitor is a great way to check video jitter coming from the Propeller, itself, as it doesn't suffer from a finite pixel grid. Also, if you are sending an LCD a non-native-resolution signal, it will have some degree of trouble registering the pixel boundaries, resulting in visible jitter.

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    Chip Gracey
    Parallax, Inc.
  • James NewmanJames Newman Posts: 133
    edited 2008-01-21 07:31
    Sorry for the late reply guys, actually forgot about this... tongue.gif

    I find that using bright colors seems to cause the bleeding. If I use palette colors containing any '3's I get alot of it. I am actually using a crt monitor, so it's not that.

    I don't have any capacitors on the board aside from the one(s?) that are already on the Proto board when it arrived. Are you suggesting that I add a small ceramic capacitor across the vss/vdd connections going to the vga db15 connector? I have to admit, being quite a newb when it comes to electronics I think I've almost no knowledge on how I should choose capacitors, and their values. I understand that some are polarized, and the importance of that. I understand that everything that can carry current has a capacitance, and that in some cases I should bleed that off with a resistor or capacitor... but as far as choosing the right one... I'm lost. It's not too important in my current project, but I have another on the back burner that deals with alot of switching, and I would like to be able to take care of the possible problem, or atleast heat/energy lost from charge being trapped in all my wires and such...

    So, if someone had a great resource on capacitors, I would be greatfull [noparse]:)[/noparse]
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