Hi

I have been considering building a continuity tester for Cat5 network cables (which have 8 individual wires) for a while, but can't come up with a suitable solution.

Most of the designs I have seen rely on two of the individual wires to be intact, in order to complete the circuit, and light the LED, telling you that pair is ok. Obviously, you don't know which of the two wires (or possibly both) is not connected.

The other way I have seen it done is to have a common ground, or common anode, and have 7 LEDs connected to the other wires. However, this won't show up a problem if the common connection is the one that is out. I suppose I could feed the outputs into logic, then if none of the other wires returned an output, the logic could give an output showing that it was the common that was out. But what if it wasn't - what if it was the other seven that were out? It seems like a bit of a bodged way to do it.

In both methods, there is something that is plugged into the other end of the cable - either simply wires connected together, or sometimes transistors and the like - I am not bothered about which, however I would rather that it drew power from the main tester unit, instead of having its own power supply.

Only other requirements are that the output display should be on the main tester unit. Power should be 9v or less (need to use batteries), adn as such I would prefer to use only CMOS type ICs.

Anyone any better ideas?

I would prefer to avoid PICs, because I don't really know alot about them, and I don't have the cash to start learning!!

Thanks

Tim

P.S. Below is an example of the sort of circuit described in paragraph 2.

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Here is one alternative -- something that I cobbled togetjher for another site a while back...

 

thanks

but...

Correct me if I'm wrong, but your design relies on both wires of the pair being intact? i.e. if the meter indicates that the wire is not complete, you still don't know which wire of the pair is broken? I was hoping to avoid this.

Thanks anyway

 

Hello,
Here is a link that may be suitable for what you are looking for:
http://www.reed-electronics.com/ednm...92498/20di.htm
Look under " Cable tester is fast and cheap" and click on Figure 1.
Hope it helps.
Barry.

 

As you said, most of the designs out there are similar in this manner. Think about the reality of the situation for a minute, and you will begin to understand why this is so. If you have a LAN cable with an open, that open can be in one of three possible places -- at either one of the end connectors, or somewhere along the length of the cable.

If the open is at one or the other (or both, for that matter) of the connectors, you're going to repair it by replacing the connector. If the open is somewhere along the cable length, you are most likely going to repair it by replacing the cable in its entirety, or by identifying the specific point (location) of the cable break (open) and using some sort of splice there. It's very unlikely that a proper cable splice would be made in only one of the wires in the cable, just because of how clumsy that can be. It is far more likely that the cable, if it is to be repaired, would be cut through at the point of the break and appropriate repairs would then be made to all eight wires. It is also very highly unlikely that an internal wire will go open in a TP LAN cable without some visible indication of damage to the cable sheath and/or damage to another wire.

With that in mind, other than for the purely academic purpose of knowing which specific wire is involved, it really doesn't matter which wire it is. For all practical intents and purposes, the two wires of a given pair are to be considered two halves of the same circuit. All that really matters is whether or not the pair is intact.

 

hmm, hadn't thought about it that way. Good point.

Thanks guys

Tim