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VGA Connector Question — Parallax Forums

VGA Connector Question

mynet43mynet43 Posts: 644
edited 2007-10-22 01:00 in Propeller 1
I'm designing a Propeller board with a VGA connector. My goal is to use only 3.3V power.

I noticed that both the Demo Board and Proto Board schematics show +5V connected to pin 9 of the VGA connector.

When I looked up the spec for the pinout of a VGA connector, pin 9 is shown as not connected to anything.

Does anyone know why they're using +5 volts on this pin?

If it's not needed, that will solve my problem.

Thanks for your help.

Jim

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-22 00:06
    Here's what I found on the web:

    VESA DDC compliant monitor connector
    If your computer graphics card has plug-and-play monitor support, then your computer has a VESA DDC monitor connector. VESA DDC standard defined that monitor connector pin 9 can be used as optional +5V 300 mA power supply from graphics card to monitor (the VGA connector ground is at pin 5). The standard does not define that there must be +5V supply at that pin. If you are making small circuit for just yoour on computer, you might want to check this option.

    Remember that the VESA DDC standard demand the devices which take power from th graphics card use special VESA DDC modified version of DB15HD connector which guarantees the correct plug-in sequence of power ground and signal pins.
  • NewzedNewzed Posts: 2,503
    edited 2007-10-22 00:06
    You don"t need to connect 5V to the DB15;· however, you should have a 5V regulator in front of the 3.3V regulator.· It reduces the heat on the 3.3, and also, there are many peripherals, such as the DS1307, the 595 shift register, that need 5VDC to operate.

    Sid

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    That is why they call it the present.

    Don't have VGA?
    Newzed@aol.com
    ·
  • mynet43mynet43 Posts: 644
    edited 2007-10-22 00:17
    @Mike
    The only use for this connector is for debugging output to a small LCD monitor. It's been working fine with the old-fashioned DB15 connector, so I assume it'll work without the +5V. Let me know if you think this is a problem.

    @Sid
    The only things I'm driving on this little board are the Prop and a TI Sound Codec Headphone Amplifier, so I don't think it will use enough power to overheat.

    I'm using a surface mount regulator with 800ma output.
  • mynet43mynet43 Posts: 644
    edited 2007-10-22 01:00
    I disconnected the +5V from pin 9 of the VGA connector and ran a test program.

    It worked fine, with a nice clear display.

    I think I'll go ahead without the +5 for this design.

    Thanks Mike for clearing up the spec for that pin. It sounds like it's usually not needed for Propeller applications. Although there's an interesting point in what you said. Do you know if the Demo and Proto boards use the special connector you described?

    Jim
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