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4-Wire Cable Tester

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Mike Caldwell:
As much as I like a good DIY project and I have built many RAT already makes an NL4 version of their XLR "RAT sniffer" cable tester.

Scott Helmke:

--- Quote from: Steve M Smith on July 10, 2019, 03:15:01 AM ---Here seems like a good place to post my version of an XLR/Phantom Power tester if anyone is interested...




Steve.

--- End quote ---

Wow, pretty clever design! 

I just carry around a vastly simpler tester, two LEDs on a bare male XLR insert - not as comprehensive, but allows finding many problems.  Plus I can give one away without missing it.

Steve M Smith:

--- Quote from: Scott Helmke on July 10, 2019, 10:08:05 AM ---Wow, pretty clever design! 

I just carry around a vastly simpler tester, two LEDs on a bare male XLR insert - not as comprehensive, but allows finding many problems.  Plus I can give one away without missing it.

--- End quote ---

I do have another design which includes an opto transistor and just one LED.  The LED only lights if everything is ok.  All other possible faults cause the LED not to light.  That's all you really need in a live situation.

I designed the three LED version before I was aware of the Dave Rat version. I have had a couple of conversations with Dave via e-mail who was very supportive, rather than most manufacturers who would be protective of their product.  I pointed out that I wasn't competition and I was only making them for friends.


Steve.

Frank Koenig:

--- Quote from: Steve M Smith on July 10, 2019, 03:15:01 AM ---Here seems like a good place to post my version of an XLR/Phantom Power tester if anyone is interested...
--- End quote ---

This is very nice as it is diagnostic and not just a go/no-go tester, and I could see it useful in the field. It does not, however, detect perhaps the most insidious cable of all, which is the one with 2 and 3 swapped. Then again, if you start off with correctly wired cables this is unlikely to happen on its own.

I wrote a little R program that can simulate a tester with all permutations of miswiring for any number* of wires and a fixed external arrangement of LEDs. The 4-wire tester above appears to pass.

*Well, not any number, as it's of N! complexity :o

--Frank

Steve M Smith:

--- Quote from: Frank Koenig on July 10, 2019, 11:35:27 AM ---This is very nice as it is diagnostic and not just a go/no-go tester, and I could see it useful in the field. It does not, however, detect perhaps the most insidious cable of all, which is the one with 2 and 3 swapped. Then again, if you start off with correctly wired cables this is unlikely to happen on its own.

--- End quote ---


That is absolutely correct.  The Dave Rat/Sound Tools XLR sniffer can't detect that either when used with ordinary phantom power.  However, it can if you use the battery powered sender unit with it as it puts two different voltages on pins 2 and 3.  I could also do that with mine but decided not to as in reality, as you point out, cables don't re-wire themselves, they just short out or go open circuit. The swapped connections it does indicate are just extras which might be useful sometimes.




Steve.

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