RGB composite sync Amplifier from 0.7vpp to 4vpp

Discussion in 'General Electronics Chat' started by xnihilo, Jan 9, 2010.

  1. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    Hello,

    I need to amplify VGA card sync output.
    The VGA card has 0.7vpp horizontal and vertical sync connectors.

    I need to connect my VGA card to an arcade monitor which expects Composite sync with level between 1 to 5VPP negative polarity.

    I need to combine the two sync signals (vertical and horizontal) and then amplify from 0.7Vpp to something like 1~4VPP.
    The sync signals have negative polarity.

    Combining the signal should not ve so difficult but I have no idea of how to amplify the signal.

    Could anyone help me out with that challenge?
    Thank you very much for any hint.
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    If the monitor takes a standard composite signal, it should handle 1V p-p.

    Doesn't you video card have a TV (composite) output connector? Many do, either as a phono (RCA) socket or a mini-DIN with an adapter to a phono socket.

    With that, it should be a direct connection.
     
  3. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    It is an arcade monitor.
    It has R,G,B and sync inputs with levels of 1 to 5vpp.
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Right, the monitor is an arcade monitor.

    What rjenkins was saying was your VIDEO CARD most likely has a composite(TV) out. That way you need no conversion.

    And for the price of Composite-ready video cards, ~$20, you should go that route.

    Unless you REALLY want to build the adapter. But you could really screw things up. "Releasing the magic smoke" from your arcade screen could be a definite possibility.

    Are you hard-set on building this?
     
  5. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    You still don't understand.
    It is an upright arcade cabinet monitor. It has NO composite video input.
    It has 5 wires: R,G,B,sync and GND. That's it.

    Moreover composite video is a PAL signal, whereas RGB produces clearer image.

    Anyway, I need to amplify my sync signal...
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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  7. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    I'm looking for Synch signal amplification.
    At ultimarc they have a CGA amplifier which will cost me about 50 USD. I wish to make a simple sync amplifier...
     
  8. SgtWookie

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    Jul 17, 2007
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    Last edited: Jan 17, 2010
  9. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    Thank you. I already have visited this page.
    Which of the two circuits should I use? The one without the BC547? It seems the VGA sync is a TTL level signal 0 or 5V... so the 74LS86 chip should be enough, is that correct?
     
  10. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    According to what I just read, the VGA signals, except for R,G and B are TTL levels, so I don't need to amplify it, just combine V and H sync.

    I guess I got it right.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    It looks to me like you could simply add in the other stage if necessary.

    Pretty cheap solution.

    Make certain to use 0.1uF bypass caps across the Vcc/GND terminals of the IC's used.
     
  12. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    Hello,

    What would be the use of the other stage exactly??
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Lower output impedance. There's a limit to how much TTL IC's can sink or source. Transistors are much more capable. Ideally, your converter should have an impedance of 75 Ohms to match the impedance of the cable and the monitor. If there is an impedance mismatch, you might get "ghosting" caused by ringing on the cable due to the mismatch.
     
  14. xnihilo

    Thread Starter Active Member

    Nov 20, 2008
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    SgtWookie,

    Thank you for answering all my question, I appreciate it.
    I'm sorry if my questions look dumb, I don't know much about electronics so that's why I'm seeking for some help.

    I'm not building a big project, I'm just trying to connect a PC to an arcade monitor to run arcade games with an emulator and trying to have a good picture quality.
    Can I ask you what you would advise me, regarding the two schematics on the first link you gave me.
    I successfuly connected the VGA card to a TV as the levels were the same.

    As the VGA sync signals are TTL level, I don't need any amplification, just combining the two sync signals (V and H sync to create a composite signal). I might have used the Composite video output to get the sync signal but the level is incompatible with the arcade monitor.
    I guess combining the VGA TTL sync signals should be fine but then, I still don't understand why I should user more circuitry than just the 74LS86.

    Please could you clarify this for me?

    ???

    Ok

    Uh? I read that VGA sync level is TL (0-5v)...

    This sounds like chineese to me

    Is that the case of my arcade monitor?
    What is "buffering"?

    Hope I can get some answers...

    Thank you anyway.

    Regards

    PS: with the circuit I'm currently using (based on diodes for sync combining and some amplifier I see ghost lines running down the screen at something like 1Hz... I think I'm amplifying what is already a TTL output from the VGA card and I might have some interference somewhere, the rendered picture looks lame and I would like to have a nice stable picture...

    On the first of the two circuits the pin 13 is connected to GND while in the second schematic it is connected to +5V... Why?

    Whats exactly the use of the two BC547? It amplifies? It acts like a kind of darlington pair???

    What if I use the Composite Video output with the LM1881N IC to get a composite signal? I don't know if this chip will output a TTL level output sync signal...

    I also read:
    And this:
    But I thought the output level was about 0.7VPP while the lines above state that it will be TTL level...

    And finaly this:
    So it is what I should use, provided my VGA card simultaneously outputs on the VGA and on the Composite output connectors...


    at: http://www.mail-archive.com/msx@stack.nl/msg13217.html

    I'm using circuits from:

    http://members.optusnet.com.au/eviltim/vga2arc/vga2arc.htm#acvid

    And it not bad but I have the problem with the ghost interference...
     
    Last edited: Jan 19, 2010
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