>Does anybody know what the electrical characteristics of Ethernet
>(10base-T) are? I'm using an RJ-45 plug in my PIC device because I
need 7
>conductors and they're cheap and durable, and I want to choose which
>wires go to what such that if Mr. Curious plugs an ethernet network
into
>my box it won't let the magic smoke out.


A very good idea!  If it fits, it should work, or at least do no harm.
(Dave's rule of connectors)

I don't remember any voltages as in power supplied on the network
connectors. The AUI port has that, but not the modular.

Signalling voltages I don't remember, but not much energy behind them.