SparkFun Forums

[cwells]

Hi,

I am currently working on a project that needs Ethernet connectivity. I cannot use a RJ45 jack inside the case that holds the electronics as it is overall physically too big. Please could anyone recommend a smaller alternative wire-to-board PCB-mounted connector (top- or side-mount) for mounting inside the case that will cope with Ethernet signalling, i.e. 100Mhz and ideally 100ohm impedance, to reduce signal reflections. A plug and receptacle solution would be OK if I can attach the CAT5e cable's twisted pairs to the plug. I appreciate that I may need suitable additional 'magnetics', as these are usually integrated into the RJ45 jack, that I am replacing.

Many thanks.

[ElectronWrangler]

Can you give me some more information? If you've got an ethernet interface and you've removed the jack, let me know what the jack part number is. If you're building a circuit from scratch, what's the part number of the physical interface (PHY) or switch you're using.

We can look in the datasheets to find hidden load resistors and magnetics.

The simple answer is, I bet you could get away with a 4-pin 0.1in header and a couple 100 ohm resistors, one placed across each pair at the connection to the PHY. You could re-use a scavenged cable, like a CDROM audio cable. Carefully remove and de-crimp the ends, and solder your pairs in an order of your choosing, then re-assemble. Then the wires would stay together.

Let me know some more info and I can get a better answer for you.

Thanks,

[stevech]

RJ-11 phone jack. but connector for cable would be special too.

for short runs, phone cables can be used.. cat-3.

[dschlic1]

You have to be careful here. There needs to be a magnetic transformer between the cable and the actual Ethernet IC. In some cases this transformer is located in the jack. You can get separately mounted transformers.

[stevech]

yes.. the transformer is inside some RJ-45's