killing ethernet connections

Why not just get a cheap hub or switch to place on that connectiona and just kill the power to it? With the prices these days, it would likely be cheaper than trying to build something and more reliable too.

I haven't used newsgroups since I was at University back in 1980, so its good to see that people are still as quick to respond as they were when the internet was young. Thank you all. Thanks for the suggestion, but cheap hubs are not that cheap. I have a budget of around £1 per unit to add this ethernet killing opton to an existing product (that does lots of other things) and I can get a simple two pole relay or a couple of optoisolators for around 25p. As to detecting the PC, there must be some current flow when the pair is shorted, it will be small, but there must be some. I can't take the hub apart and connect in to the back of the leds because of keeping approvals. The hub is too far away to fix an optodetector to the outside to "see" the led. I am sure that shorting with a relay or semiconductor device would kill the connection, but there is no point in me going ahead if I can't get approval later. I'm guessing at the moment because I still can't find the actual physical layer specification, but I will keep looking. If the data was sent on top of a continuous carrier then I could detect that, but if the pair floats when there are no packets flowing then I might be stuffed.

Is there an echo in here?

is manual, and as others have pointed out a cheap switch will stop forwarding packets when it's power is removed.

There isn't any current flowing in the cable to be able to detect PC connection, but there's usually an LED on a switch...

It's a transformer coupled 2-3 volt peak-to-peak signal with not a lot of drive capability. In fact, measuring it is probably really bad for your signal integrity. Now that I think about it, a shorted line will only see link pulses, which don't happen that often...

Is this for coax, 10BaseT, 100BaseT, or Gigabit? Each of them has separate signalling, negotiation, and duplex...

What else does this product (need to) do, maybe there's a way to do what you want...

There is no current. The cable is transformer connected to the NIC, so there's no DC at all. There's only the transmitted signal. I doubt you could create a reliable, non-interfering detector, for around £1.

That should work fine. Most likely you only need to short one direction, depending on the situation. To minimize the effect on the line, you might use a double pole relay with two poles shorted together, and the ethernet lines on the contact side.

1/10th might not do it. If you figure the attenuation on a 100m cable, your signal must be much smaller than that to qualify as shorted. 1/100th I would believe, though, without actually looking at the numbers.

Unlike about half the posts here, which belong in a TCP/IP newsgroup, this is the correct group.

Even more interesting, this question came up a month or two ago.

-- glen

I have looked back through all the topics and found "Ethernet Breaker" which seems to be what I need. Now I know that there is a transformer at each end then I think I am OK just shorting the TX and RX pairs. Mechanically I think I'll start with a standard cat5 cable, remove an inch or so of the outer sheath in the middle, untwist a bit of the orange and green pairs and use a 4-way 0.1" IDT connector to give me a tap that can be plugged into a bit of PCB with the relay on it. It would be nice to run 100BaseT through this, but it only for a PC to connect to the internet via broadband at 512k so I can actually get away with 10BaseT. I will report back here when I get something working (or give up) in a week or two. Thanks to you all.

For 10baseT that should be fine. For 100baseTX you will need to be a little careful with the wiring, such as trying to maintain 100 ohm impedance through the PC board. It should then be done with two connectors, such that the signal goes into the PC board, past the relay, and then out again, maintaining 100 ohms as much as possible.

For 10baseT you don't need to be quite that good, but try to minimize the length of the PC traces from the connector to the relay pins.

-- glen

It works! I have tapped into a 5m cat5 cable with a 0.1" IDT connector onto a bit of cheap Vero bread board with a cheap double pole relay close to the connector. I didn't bother with using two poles together to keep the data off the moving contact. I can sucessfully run

100BaseT over the link and when the relay contacts close the link leds at both ends of the cable go out, and as soon as the contacts open again the link leds come back on. I have tried to determine if the relay has any effect on the link, such as an increased error rate but I can't see any difference in the time taken to throw big files around the network. I have tried a demo version of "Colasoft Capsa 5.0 Enterprise" and it doesn't show any hardware errors on the network with or without the relay in place. Does anyone know of a suite of test software specifically for this sort of hardware testing? I have sent the prototype to my customer, so we shall see what he thinks. Thanks to you all.

Hooray!

Umm, you _REALLY_ need to certify this device to CAT5 so that it'll work on any network, not just the network you set up in the lab. Bone up on the Cat5 specs and rent a certification tool!