Trouble connecting with USB and touching printer with metal object

Hello reprappers,

I've build a i3 a few weeks ago and I'm happy printing. But there's something odd and I can't figure out why it's happening.

First wierd thing:

When I'm trying to connect the printer (mega 2560) with the PC its a pain in the ass. I connect the USB to my PC and I hear the normal USB inplug-sound. After that I plug in the power of the printer. When I do this, most of the time I hear the USB unplug-sound and then the USB error-sound. At this point I cant connect tot the printer and I have to do it all over again. If I'm lucky after a few tries nothing (no unplug sound) will happen when I plug in the power of the printer and I can connect.

That is the only way to connect the printer. I can't plug the power first and the USB second because it will always make the error sound.

Its pretty enoying to plug in and out for 10 times before it makes connection.

Second wierd thing:

When my printer is connected and fully funcional, touching it with a metal object (like a screwdriver) makes it disconnect from the PC?! I hear the USB unplug-sound and lose connection. A few moments later I hear the USB error-sound and I have to reconnect it using the method above.

I think these to problems are related but it dont understand whats happening. It seems like a grounding problem from some sort but again I dont understand it.

Does any of you have a single clue? Im getting a little ignored on this haha ;-)


Nice holidays and a amazing 2015!

Edited 1 time(s). Last edit at 12/30/2014 10:55AM by navyblueboss.

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Reprap Prusa I3 - RVS with Schufco custom head

... the GND-potential of your power supply and the PC is off some Volts -- so when connecting with the GND-pin of your USB-cable, a high current peak across the USB-shield will kill the USB-connection.

With a metal/conducting object you'll interact with this potentials too, so again a voltage or current spike will run havoc and again killl the USB-connection.

Measure the voltage between GND and the shielding of the PS, and the housing/GND of your PC against the line ground - there seems to be some weird ground connections with high currents shorting through your cable shields ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Make sure you run the PC and the printer power supply from the same mains socket, via a distribution block. Don't run anything else from that distribution block. Putting a ferrite bead on the USB cable also helps with USB ground loop issues sometimes.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I measured the shield (gnd) of the USB cable and the body of the printer. There was 4.8V?! Which means the power of the USB goes to the printer and then back trough the shield (gnd) of the USB.

Because it was 5V I was sure the Ardruino had somehow contact with the body of the printer. Turned out one of the nuts that holds the Ardruino in place touches a metal pin on the bottom of the board (which wasnt the GND). So I had a loop..

Just printed a tiny washer and the problem was solved!! (Smaller nuts would also solve it but thats more work ;-)).

Thanks for the advice, you really helped me out here.

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Reprap Prusa I3 - RVS with Schufco custom head

I bought a Sanguinololu v1.3a board to replace the fully functioning Gen6 controller in my Prusa Classic. mostly because I did stuff like this before I retired. There is info regarding the butting heads of the two power supplies, the one on the Gen6 and the one on the USB bus from the host comuter. the suggestions were to cut traces on the board and other rather drastic measures and looking at the schemtic I saw that cutting the 5V wire in the usb cable accomplished the same thing. I melted the jacket about an inch and a half and spread the shields(foil and weaved wire) exposing the four wires(white,green,black and red) and snipped the red wire and folded it back. my thought was a cable was cheaper than a board and it was worth a try. It worked. keeping the black wire allows a common(no voltage offset) between the two units and so the communications worked normally. perhaps the arduino mega 2560 board has a similar construct. Just a thought.....