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Solved LCD screen power source

Discussion in 'General Questions' started by joea, Apr 5, 2021.

  1. joea

    joea Active Member

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    Minor concern. Adding the LCD screen was fun. Not sure it really does anything useful, but it looks nice.

    However, as long as the USB cable is plugged in, at both ends, the display is "on", even with the ac power switched off.

    Is it possible, advisable, to change the power source for the board, so it only glows when the AC power is on, or is that just how it is?
     
  2. Wesley Knapp

    Wesley Knapp Active Member

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    That's how it is but you can get (or make) a usb cable with a switch that disconnects power.

    Sent from my Pixel 5 using Tapatalk
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    If you do NOT want it powered from the USB then as @Wesley Knapp says -- get a USB power switch. Example here:

    https://www.amazon.com/Switch-Extension-Upgraded-Strips-System/dp/B07T9BRNHW

    edit: Actually in that case it shuts off both data and power so no help for your case.
    It is fine to run them both on the RAMPS because it uses a diode to select the one providing the highest voltage and does not allow them to 'buck' against each other. But if you are really concerned remove the D1 diode. Read here: https://reprap.org/wiki/RAMPS_1.4#D1.2C_D2_-_Diodes
     
    #3 mark tomlinson, Apr 6, 2021
    Last edited: Mar 17, 2023
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    One thing to be careful of -- some USB power switches ONLY pass through power and not data. The one I linked does both.
    If you use one that does NOT pass through data then while the power will get to the printer, the slicer can not.
     
  5. joea

    joea Active Member

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    I know this is an old thread, but never really addressed the issue. I guess I don't understand something here.

    All I really want to do is avoid "mixing" the +5v power from the printer and the USB cable to avoid any "noise" or other electrical problems that I have read about. Most all say they should not "mix":

    I should look at the schematics again to see if there is some internal way to do this, I know my other printer has the two supplies "isolated". Seems I should be able to do that on the Robo as well, through some existing jumper or careful cable (not USB) snipping.
     
  6. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Use the USB power switch referenced above or modify the board to remove the diode that handles the shift from the power supply to the USB power (on the ramps board).

    https://reprap.org/wiki/RAMPS_1.4#D1.2C_D2_-_Diodes

    D1 diode must be removed to totally isolate the two.
     
    #6 mark tomlinson, Mar 17, 2023
    Last edited: Mar 17, 2023
  7. fred3d

    fred3d Member

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    It's been a while since I've pulled the R1+ out of the pile in the junk room, but I think I wired inside the case to the mains power leads a USB power adapter. Since it's upstream of the main power supply, it's as clean as the mains source and has no interaction with the printer's power supply. Being placed inside means that the case power switch cuts power to both devices at once.
     
    mark tomlinson likes this.
  8. joea

    joea Active Member

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    I'll look into D1. The switch would still supply +5 while "on" and now allow me to print when "off".

    Will also look into adapters I can modify or other ways to isolate the +5v line in the USB cable. All I want is for the LCD, backlight at least, to be "off" when when the printer power switch is turned off.
     
  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yep, more about it here too: https://reprap.org/forum/read.php?219,468926

    D1 is the key :) You can make the RAMPS only powerable via the USB.
     
  10. joea

    joea Active Member

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    But I want the opposite, only powered when the printer power is on. I just want to cut power from the USB to the LCD. If I had a "real" circuit schematic it might help. I'll check your link.
     

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