ethernet cables, why remove the ports?

In the very near future I will have all the parts to build a Mendel. I wanted to build the Mendel first since it is VERY well documented, anyways I just received the electronics from Makerbot, and i am reading about the modifications needed to make it reprap compatible.

My question is why am i removing the ethernet ports? Why not just use them? Is there a problem using ethernet cable to connect things? If there is nothing wrong with the cable then i will just use them.

Someone please let me know if it matters... thanks

I haven't finished mine yet, but I don't think there's any technical reason to do the modifications. Those changes are basically just to make it a lot easier and cleaner since the ethernet cables are kind of bulky and difficult to plug in.

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Tony Buser http://tonybuser.com * http://reprap.org/wiki/User:Tbuser#Projects

gr0k Wrote:
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> I haven't finished mine yet, but I don't think
> there's any technical reason to do the
> modifications. Those changes are basically just
> to make it a lot easier and cleaner since the
> ethernet cables are kind of bulky and difficult to
> plug in.


ok thats what i thought, i was just worried the wire might be too thin or something like that

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My Reprap Project "Work In Progress" Walkthrough: [echovoice.com]

Another I think is that when people are buying very short ethernet cables is they have a tendency to purchase swap over patch cables which are not a one to one connection.

Using a swap over cable has been reported to kill the opto endstops.

Ethernet cables (CAT-5e is typical) have four twisted pairs and were designed for differential signaling and with matched driver output and receiver input impedances (i.e. 100 ohms differential).

The signals on the stepper motor controller really isn't a good match for this. The signals are single-ended and don't have matched termination impedances. Taking two single ended signals and twisting them together for the length of a cable increases the coupling between these signals which increases interference and decreases signal integrity. This is really opposite the purpose of differential signals and use of twisted pair cabling. However, this doesn't mean it won't work. It just isn't optimal.

Note that one could take untwisted cable and terminate it with RJ-45 connectors to avoid the increased coupling due to the twisted pairs of CAT-5e cables.

Note also that the flat ribbon cables are also not ideal. Wires are held in close proximity for the length of the cable which also results in coupling between the signals. If one were concerned about signal integrity with single ended signals run through ribbon cables then it is common to allocate pins such that every other wire is a ground (signal, ground, signal, ground, etc.). However this isn't possible either given the current connectors/cables.

So, sorry to say, that from a signal integrity point of view there isn't a clear winner either way. If it works (and it clearly does for many)... live with it. But this is something that can, and should be, improved in future iterations (in my opinion).

TC

The extruder controller gets power through the motherboard through the Cat5 cable for the makerbot version. The reprap version, the motherboard is powered through the USB-TTL cable, but the extruder controller gets power directly from the power supply. This is why the RJ45 connectors are usually removed for reprap config.