Newsgroups: comp.dcom.lans.ethernet
Subject: Re: Ethernet breaker
References: <[email protected]>
"Rich  Noonan"  writes:

> I'm looking for a device which could act as an ethernet breaker switch
> based on the application or loss of power to that device.  On one hand
> we could accomplish what we need with a low-cost switch and two cables.
>  However, in our application and environment this would introduce
> several new problems.  What I really need is a two port fast ethernet
> repeater that I could cut power to and break the link.  Of course, such
> a thing doesn't exist (or does it?).
> 
> Any suggestions on a part that could fill this role?  We could probably
> design and build a mechanical switch to break the link, but I'm trying
> to find something we could buy before going down that road.

No ready made part recommendation. 
Basicly you could build what you need by combining an Ethernet 
switch and an relay connected to PC serial/parallel port 
(in case you have PC nearby that runs the application). 

Just connect the switch between the power source and the switch. 
The computer control power to switch on/off. 
If your switch uses low voltage power supply (like those small 
"wall wart" powered switches), then just adding a relay to one of 
the power wires is preaty easy and safe. If you know how to safely 
build mains powered things (and you have necessary qualifications 
to do that) then circuit for controlling mains power to device is 
another option. 

You can find some information on interfaceing relay to serial port at 
http://www.epanorama.net/circuits/rspower.html 

Another interresting RS-232 port hack:
Marko M�kel�'s electronics projects: RS-232 Solid State Relay
http://www.funet.fi/~msmakela/electronics/relay/ 

Parallel port interfacing made easy
http://www.epanorama.net/circuits/parallel_output.html


There are also commercial products and electronics kits  
for PC interfacing.  

And there are companies that make remotely manageable 
power switchers that can take controllign signal 
from almost everywhere (serial port, Ethernet, 
telephone line, cellular phone SMS text message etc..) 


besides using switch and turn it's power on/off you can use 
the relay directly to cut the Ethernet signals.. 
A relay that cuts the connection on all the four signal carrying 
wires (applied to 10Base-T and 100Base-TX) shoudl do the job. 
Keep in mind in the circuit design not to cause too much 
impedance mismatches and crosstalk for the signals. 
Many normal signal relay contacts should carry Ethernet signals 
acceptably. 
Other way to cut the connection woudl be to short the signal 
wire pair (one relay contact on TX pair and other on RX pair). 
Short circuit should stop the Ethernet signals from getting 
to other end, so should look same to cards that line is cut. 


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/