Hi,

I want to install a RS45 plug in my car, giving both access to serial and ethernet (a universal plug).

Ethernet uses pin 1&2,3&6 for RX/TX

This leaves pins 4,5,7 & 8 available for serial.

So I figure I can hook up ground, 12V, TX and RX on those, like this:

"Empeg end" to "plug end" below.

Ethernet RJ45 male -> RJ45 female:

Pin 1 -> Pin 1
Pin 2 -> Pin 2
Pin 3 -> Pin 3
Pin 6 -> Pin 6

Serial plug male DB9 -> RJ45 female (the same as above):

Pin 4 (ground) -> Pin 4 (plus external wire to car ground, due to fault in empeg serial harness)
Pin 5 (dsr) -> Pin 5 (plus external wire to car 12V+ batt, due to fault in empeg serial harness)
Pin 2 (rx) -> Pin 7
Pin 3 (tx) -> Pin 8

Now, the question is, the 12V coming out on pin 4&5 should'nt harm any networking equipment, as these pins are left unconnected in the NIC. But can this be trusted to be so?

Does this look right?


Your comments please,



Lars

Not sure if it is safe but it is not uncommon. Several Cisco routers and other network equipment for that matter use Rj45 connectors for (serial) console ports. So I guess it is not uncharted territory. Combining them together is not as common though, in fact never seen that before. But I have to wonder if it would work as expected. The cables are twisted for a reason after all. I think it would be very likely that the signals would cause interference on eachother. If it is enough interference to impede the working of the ethernet and/or serial link is hard to say.

I would say if you do it, just use 2 RJ45's, that to me sounds like a better option. There is plenty of faceplates and brackets around that hold 2 of these for network-cabling-infrastructures. You could make it look fairly neat and professional with these.

Cheers,
Hans


Mk2 - Blue - 080000431

1) Make sure the correct pairs are twisted.
2) Make your oou use own cable. Will you use eth and serial at the same time? Then you could just make a y-cable making sure yourself that power doesn't enter the NIC. If you use only Eth, make a cable where the serial lines are broken.

Interference won't be a problem at these lengths of cable.
For instance BreezeAccess (www.breezecom.com) outdoor-solution uses these signals in the same cable.

MArius (Escort cab + MarkII)