Can I put the ENC28J60 16 feet away from the host µC? Or Can I put the ethernet Jack 16 feet away from the ENC28J60? What’s the limit on these things?
signal integrity is the challenge. You can do all sorts of crazy things, and they may work, but friends don’t let friends do weird stuff like this, so no, none of what you proposed is possible. Ethernet cables on the otherhand, they do come in 16ft or greater lengths, and they are relatively hardened for such distances, so you should just thing of your problem in that manner (seriously - solve the problem with something someone else designed to be suitable for that task)
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So therefore, use an ethernet extension but put the jack and magnetics on the main pcb. Okey dokey.
And, with enough switches, you can take your ethernet a LONG way. 100BASE-TX specifies a maximum distance of 100 meters per segment.
Wait, hang on. Can’t I use an ethernet cable to extend the range between the ethernet phy and the actual ethernet jack?
no. Well, again, the real answer is maybe. It is not designed to do that. It may work. Thousands of other designers don’t. Have you searched for Ethernet PCB design practices? I would bet such a separation is not what they recommend, it’s probably more “make it as short as possible”.
I still come back to - what problem are you trying to solve. You keep saying you want to do things but don’t really explain why the “accepted” method won’t actually work for you. If you keep asking questions, we’ll keep answering the question, but if you tell us what problem you’re attempting to solve we might come up with solutions…
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Oh, I didn’t explain the problem; sorry
In order to get the best of both worlds, I’ve decided to use a .netmf module (from GHI) as both the µC that operates the robot and as the platform for the web communication. However, this means that the .netmf module has to be deep within the robot; 16 feet away through the cable chains to the outside enclosure. The robot must have ethernet. It must be accessible via http, and a web interface. These are hard requirements. I plan on using the G120E with the ethernet phy. So the problem is: How do I get the ethernet signals from the pcb to the outside enclosure.
I can
- Put a RJ45 jack on the pcb and run an ethernet extension to the outside.
- Put a 10 Pin header on the pcb and run an ethernet + 2 wires to a RJ45 jack mounted on the outer enclosure.
I would much rather do solution 2 because then I can get the 2 activity lights on the outside of the robot instead of within the core. I know solution 1 will work, but will solution 2?
Easy.
Bluetooth module on robot + standard Ethernet module. Bluetooth lights up indicators on a remote Bluetooth device - no wires needed.
Sorry, I just don’t think you can EVER reliably run signal wires over that kind of length of cable especially when you say “robot” that implies motors which implies all kinds of EMF problems.
Bluetooth module costs money and pcb space. Perhaps, ethernet module + 3 wires to the external ethernet leds?
oh so you want LEDs for your activity on the Ethernet cable? Easy. Just look at the switch that you’re plugged into, instead of the plug at the bot end. Same result !
So I went and grabbed a random app note from a manufacturer. First one I read, http://micrel.com/_PDF/Ethernet/app-notes/an-111.pdf, says stuff that implies you’re never going to decouple the two - concerns about capacitance and impedance imbalances, obviously crosstalk etc become an issue too, and managing that on a long aerial (cable) will be “fun”.
In all honesty you might have better luck with a line driver extending the SPI connection to a ENC28.
I hope it doesn’t come to that. I have a spinning magnetic field behind the PCB; so I guess I can only do so much regarding EMI. I guess that would mean I can’t use the G120E since that has the phy on board already. G120 + long SPI it is then.
We found that with the Hydra you can’t even get away with a 20cm cable length between the main board and ENC28. Only the 10 and 15cm lengths would work. Since the firmware requires initial communication with the ENC28 during bootup, the whole thing would just be dead. Took us a while to figure out it was the cable length.
@ LukeG - Well that answers that question 