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I've noticed before that when I use a standard USB-cable to connect my Creality Ender 3 V2 printer using its USB port to a Raspberry Pi 4 and powered off the printer, that the LCD screen of the printer stays turned on. Even when the power cable is removed from the power supply of the printer, conclusion: the LCD screen draws power from the Pi over USB.

Although that seems like a horrible design for the v4.2.2 Creality board in my opinion I bought a simple PortaPow Power Blocker USB connector as shown below:

PortaPow USB power blocking connector

I could imagine there are other solutions to this but my question is: Is cutting the power over USB indeed the right approach? Is it common to do that for this type of printer and is it indeed the result of bad design by Creality?

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If your question is whether a data-only USB cable is required in order to keep the LCD screen off until 12 V power is applied, then the answer is yes. However, then realize that you won't be able to flash new firmware onto your 3D printer board nor upload new 3D prints until 12 V power is applied again. Every time you want to upload a new 3D print to your printer, you'll have to turn on the heavy power supply attached to the wall. In the long run, this may use more energy, if for example, you forget to turn off your printer.

Ultimately, I think that I agree with you though, that this is a questionable design choice. On the other hand, 3D printers emit a ton of microplastic, and you probably shouldn't be using them in an environment where the light from an LCD screen would bother you. (Not in a bedroom, for example.)

On most 3D printer boards, everything 5 V and below is powered by the USB cable, or the 12 V power supply. If one is active, they will be powered. If you had relays attached to 5 V pins, for example, they would be "on" when the USB cable is attached, just like the LCD screen, and just like all the "thinking" parts of the 3D printer board. The "muscle" like the motors and heaters rely on 12 V and obviously aren't powered by USB. Everything 5 V and below is flexible in that way, it can be powered by USB or 12 V, but 12 V can only be powered by 12 V. (This is only within the context of 3D printer boards... there are other things called boost converters that can convert 5 V to 12 V, but there is not enough power from USB to do that to power a 3D printer.)

Some boards like the SKR mini v1.1 have a movable jumper that you can use to choose whether things like the LCD screen are powered by the 5 V USB input or the buck converter attached to the 12 V power supply. (However, this is a really cheap board.) With this board, you wouldn't need a data-only USB cable. I don't recommend this board, however.

It might also be possible to turn off the power provided to all USB ports using software on the Raspberry Pi.

You don't need a special adapter like that, either. You can use a small and removable piece of masking/duct tape, and some tweezers, to turn any USB cable into a data-only USB cable.

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  • $\begingroup$ I don't understand the inability to flash firmware actually. Nor is it about the light of the screen. The brightness can be reduced to 0, effectively turning the screen off. My main issue is that the screen stays on when the printer is off, that just seems wrong. Potentially drawing too much power from the Pi too. $\endgroup$
    – Bob Ortiz
    Commented Dec 9, 2023 at 17:24
  • $\begingroup$ If the printer’s main switch is set to is off, and the usb cable is data only (not providing power), there will be no power to flash firmware or upload 3d prints to the board. $\endgroup$
    – K Mmmm
    Commented Dec 9, 2023 at 18:36
  • $\begingroup$ The LCD draws a negligible amount of power $\endgroup$
    – K Mmmm
    Commented Dec 9, 2023 at 18:36
  • $\begingroup$ “Flashing firmware” means updating the microcontroller code on your 3D printer to let it to new things (like maybe add an activatable heated chamber or an exhaust fan) $\endgroup$
    – K Mmmm
    Commented Dec 9, 2023 at 18:38
  • $\begingroup$ I understand what flashing is but I don't see how flashing is relevant to this question at all 😅. By 'potentially drawing too much power' I meant we don't know what else draws power on the main board, the USB cable is connected to the board, which powers the LCD. I think the use case of USB cable should always be data only in the sense of 3D printers. $\endgroup$
    – Bob Ortiz
    Commented Dec 9, 2023 at 18:50

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