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Keyboard / VGA from a 3.3 volt source.. — Parallax Forums

Keyboard / VGA from a 3.3 volt source..

KPRKPR Posts: 189
edited 2009-04-23 14:17 in Propeller 1
I just built a YBOX2 kit and just realized that it doesn't have a 5 volt source.. Is there any way I can still get them to work with the 3.3 volt source or am I out of luck?

Abysmal

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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-04-22 23:06
    All you need is to add a regulator for 5V. You're not talking about a lot of current. You could easily glue an LM2937-5.0 on top of the existing LM2937-3.3 and connect the ground and input pins together. You'd need a small tantalum filter capacitor, but that's easy to mount and connect in, probably by soldering directly to the ground and output pins of the regulator and just letting the capacitor float in the air. Since the tab is ground, you could even use a longer screw and spacer instead of glue to hold the 2nd LM2937 in place.

    I just looked at my LadyAda version of the YBox2 and it uses an LM1117-3.3 regulator with the tab soldered to the board. I'd use an LM1117-5.0 regulator and glue it, then connect the ground and input pins together (between the two regulators). The pin assignments are different between the two regulators. Consult the datasheet for specifics.

    Post Edited (Mike Green) : 4/22/2009 11:18:30 PM GMT
  • KPRKPR Posts: 189
    edited 2009-04-23 00:05
    I'm thinking of adding a piggyback board then.. for the keyboard and mouse and vga... i'll just put the regulator there and just feed off of power of the ybox2..

    thanks Mike

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  • Nick McClickNick McClick Posts: 1,003
    edited 2009-04-23 00:25
    I don't know about VGA, but many keyboards / mice work just fine with 3V. Not all, though - ymmv

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-04-23 12:57
    Most of my keyboards are ok on 3.3V, but not all. Other way round for the mice though.
  • KPRKPR Posts: 189
    edited 2009-04-23 13:00
    For what its worth, I was chatting with Harrison Pham last night and asked him how he did his VGA Out on his propIRC, and asked if he had dual voltages ( 3.3 & 5 ) and he said no.. he just didn't connect the 5 volt pin on the VGA.. So I'll try it that way as well..

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  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-04-23 13:02
    Should work. You might have to turn off and on the power button
    if the monitor goes into sleep mode. (newer monitors)

    OBC

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  • Brian FairchildBrian Fairchild Posts: 549
    edited 2009-04-23 14:17
    The 5v on a VGA connector has a different purpose to that on a keyboard or mouse. On the keyboard and mouse it's there to power the device and needs a decent amount of current, around 100mA for a keyboard. On a VGA it's just a signal to the VGA and is a very low current. You could easily fake the 5v to the VGA if you needed to. Just add a small diode/capacitor voltage doubler onto the 'H' or 'V' sync signal and you'll be able to generate the necessary voltage for very low cost.
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