3B+ Direct connect to MK3 Einsy


What is the problem?
Direct connection works when all 6 pins are used to connect the pi to the einsy. However, i wanted to retain use of the external power supply for the pi so it was not dependent on the printer being ON to function. When removing the 5v and GRND pins for the equation, Octoprint will not connect to the printer.

What did you already try to solve it?
Nothing. It works with all 6 pins, it does not work with only 4 pins. I dont know what else to try.

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)
ocotopi 0.15.1, ocotoprint 1.3.8 on rpi 3b+

The reason i wanted to have the power seperate from the printer is because i wanted to be able to use the PSU control plugin to remote shutdown the printer. But from a clean cable management standpoint, having a direct connection inside the case (custom pi + einsy case from thingiverse) is much neater, and more attractive than running a USB cable from the bottom of the case to the top of the case, just to make the USB connection. Since it only seems to want to connect when using all 6 of the direct connection pins, that would probably lead to a corrupt SD card when cutting the power to the printer, without a proper pi shutdown.

So, basically, why are all 6 pins required for Octoprint to communicate with the printer? I can skip the 5V and GRND and give it power over its normal power supply. In my mind, it should still have everything it needs to be powered AND talk to the printer directly.


You can power both devices from different sources but the GND must be connected because GND is the common potential for almost everything.
If you don't connect the GND there are different references on both devices for all the data signals, that wouldn't work.


Thanks Bernd. So there is no harm in connecting the normal mini USB power cable from the wall no power the pi, and also connecting JUST the GRND between both pi and einsy? nothing will blow up?


Nothing should blow up - but don't sue @BerndJM or anyone else on here if it does for whatever reason after all :wink:


that doesnt sound very legally binding :wink:

ill give it a shot. worst case i guess its only $40 for another pi.

thanks for the help!