Put tape on the 5V pin - Why and how

It looks like a dumbed-down version of my project.

Yep, dumbed down, but they work, I've just ordered a stack of USB breakout boards from Aliexpress to make the next batch. Might even make a 3D printed case for them :smile:

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They don't work for my own Robo control board (Robo 3D). It will throw an error in OctoPrint if there's no 5V line.


I tried to apply this tape fix on the cable to my Prusa MK3S.
But it doesn't work: the octoprint can not connect anymore to the printer...

Do I have the correct understanding that the picutures on top of the page are the plug on the wire side to identify pin1 +5V?

Is it normal with my printer or I missed a trick?

Thank you for your help


Doesn't work on all printers. Doesn't work on Prusa, doesn't work on bq Hephestos 2 from my own experience.

OK I stop trying then! Thank you!

I was having occasional undervotage and other gremlins on my printer, so I was looking for a way to isolate 5V and saw the tape-pin method suggested. Unfortunately, my board would no longer communicate (2560 / Ramps 1.4). Looking at the schematic for the 2560, it uses an ATMEGA8U2 as a USB to UART converter, and on that chip, if the USBVcc is unpowered, it won't power the USB side of the converter. If you don't have 5V on your cable, no USB communications will happen. So give it 5V! But, from your printer's control board, not your Pi :wink:. Most boards should have a ton of 5V pins on aux I/O.


Just made a cable to do this on my printer and it is working great. Time will tell if it solves my undervoltage and other gremlins.

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One of the designs—on paper—which I created was something like...

  • Pi-side relay, if on, allows the Arduino to see its own 5V on that Arduino-side 5V serial pin
  • Arduino-side relay, if on, allows the Pi-side relay to have power

So basically, if either side is off then there is no communication. But if both sides are on, the 2nd relay powers the first which then allows the Arduino to see its own 5V. The Pi never sinks power but neither side are fooled into thinking the other is up when it's not.

Perhaps some cleverness with resistors such that the 5v pin was logical Hi but very little current?

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Possibly. We're mostly concerned with the current-limiting aspect of this.