I'm going to connect an RJ45 connector to my MBED for some ethernet experiments.  I remember a thread where someone had troubles with connectors that incorporated magnetics versus those that didn't, or something like that.  I want to use the breakout board and connector from sparkfun:

http://www.sparkfun.com/commerce/product_info.php?products_id=716

http://www.sparkfun.com/commerce/product_info.php?products_id=643

I see they also have a version with magnetics included

http://www.sparkfun.com/commerce/product_info.php?products_id=8790

http://www.sparkfun.com/commerce/product_info.php?products_id=8534

This is for an ESC demo in a couple weeks so I want to make sure I get the right thing.  Can anyone provide some suggestions as to which of these I should get?

thanks,

--steve

Hi Steve,

I would prefer the connectors with included magnetics.

It's saver for your hardware.

Cheers

Rolf

Hi Steve,

I ordered the version from Sparkfun with Magnets to be on the safe side. The issue I had with the breakout board and connector was trying to work out which why was which, but in the end i got it sorted (I just needed to read the data sheet basically).

So in summary, go with magnetics

M

Hi Steve!

I have used with success the transformerless approach described in the National Semiconductor application note AN-1519 http://www.national.com/an/AN/AN-1519.pdf. See page 3 of the apps note for the wiring and applendix A for the capacitance calculation. (4 x 33nf capacitors, 250 VDC to a screw-type terminal block to connect the RJ45 cable). That's all.

It works flawlessly.

Unfortunately I am unable to attach a picture with the present insert tool to show you.

Regards,

René-Jean Mercier

Hi René,

If you could explain your issues with the insert tool either here or in a new thread, or indeed in an email to support@mbed.org, I'll try and help, and also to understand why it isn't working in your case.

Regards,

Dan

René thank you for posting the link to the AN-1519 National application note.

I found it very helpful.

Just for curiosity: Is it feasible to put the mbed Ethernet signals through demultiplexers/multiplexers, onto several different "cables"? The idea would be to create a network using demultiplex/multiplex technique to make a low-cost ethernet-switch connecting more than 2 mbeds? (An mbed-Beowulf?-)

(I realise there would be other work to multiplex the interfaces)

GB

Mr. Bulmer,

Since the transformerless approach worked the first time I connected it, I didn't have to probe and therefore didn't validate the voltages swings before and after the capacitors.

Having said that, to multiplex the signals of ...say 4 mbed, I would probe the output of the mbed for DC and AC parameters, then to experiment with 4 mbed I would use something like two (2) of the Texas Instrument 74HCT4052 (Dual 4 to 1 analog mux/demux) with supply voltages for the HCT4052's taking into account the DC and AC parameters of the mbed and put the capacitors at the output of the 4 to 1 multiplexers. The HCT4052 would probably be good to 100 Mb/s, since it has a roll off of -3db at 165 MHz and around -1db at 100 MHz at 2.25 VDC supply (better specs at 4.5 VDC). The Ethernet signals are much like sinewaves.

You would also need a controller to route the signal from one mbed to the other.

Good luck!

Regards,

Rene-Jean Mercier