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#10439 06/15/02 10:45 AM
Joined: Aug 2001
Posts: 7,520
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Yep, that would sure work for five wires.

The advantage of the pairing method is that it can be extended to any odd number of wires and you don't need a ground connection, although after about 9 or so it starts to get the gray-matter in a bit of a spin trying to keep up with all the links!

If you start with an even number of wires and access to a ground connection as you described, then you can follow through in a similar way.

Here's a follow-on puzzle for you. How could you test and identify six conductors, again using only a continuity tester and making one round trip to the basement?

Only this time, you're not allowed to use a ground connection at either end as part of the procedure. Neither are you allowed to use batteries, AC voltages or anything else like that. Just your continuity tester and linking the wires at each end.

Oh, and no assistants with walkie-talkies, either! [Linked Image]

P.S. Hint: Start by combining an element of your description with an element of mine.



[This message has been edited by pauluk (edited 06-15-2002).]

#10440 06/17/02 08:53 AM
Joined: May 2002
Posts: 68
E
Eandrew Offline OP
Member
Pauluk,


I just got your last challenge. My brain is rack'n. I'll work on it. Have to leave soon. I would think you'd link on the roof:1to2, 3to4, 5to6. Then in the basement identify those loops. And then link together 2to3 and 4to5. now its one daisy chain. let me work from here, I'll write back later.-Erik

#10441 06/18/02 04:55 PM
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Posts: 7,520
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Erik,

You're likely to run into problems starting off that way; try to follow it through and you'll see what I mean.

The trick is to be able to positively identify one conductor at both ends to provide a reference point. With only one round trip allowed, you must be able to identify that first conductor from down in the basement. If you start with six wires all linked into three pairs, you won't be able to do that.

I love these sort of brain teasers, as they're a great exercise in logical thinking AND have a practical application.

Keep working on it! [Linked Image]

#10442 06/18/02 05:09 PM
Joined: Nov 2001
Posts: 280
M
Member
Paul of the UK
That was fantastic, now that is logic in its purest form.
As a side note, I was watching the History Channel, I think the title was "Science and the Swastika", during the war we and the British were worried about the Germans coming up with an A-bomb first. Unbeknownst to us the Germans had it Bass-Ackwards, but two British Scientist came up with the Critical mass of 2 pounds, Which worked. The Germans had this idea of it being huge amount of Uranium which no one could even contemplate...
anyway great logic

-Mark-

#10443 06/19/02 03:49 PM
Joined: Aug 2001
Posts: 7,520
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Member
Mark,

I've never heard about the A-bomb thing. We have a History Channel on satellite over here; quite fascinating at times.

I claim no originality for the wire ID problem. It's just one of the tricks that you pick up working as a telephone engineer.

The modern phone cable is pretty much foolproof with each pair identified with both colors, e.g. pair #1 tip=white w/blue bands, ring=blue w/white bands.

But the older style cable just used solid colors on each twisted pair. So if someone managed to untwist the pair (sometimes while trying to be "helpful" !!!), on a 25-pair cable you were left with 5 plain white wires, 5 blue, 5 green, 5 red, etc.

Often it was possible to apply tones or other test signals, but occasionally there was nothing for it except to trace out using just a continuity tester. If you were working alone, tricks like this saved a lot of legwork.

#10444 06/19/02 04:12 PM
Joined: Nov 2001
Posts: 280
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Member
Paul

Well ever since I read you first post I have been keeping my continuity tester handy.
A method like that comes in handy for sure.

Mark

#10445 06/19/02 09:22 PM
Joined: Oct 2000
Posts: 5,392
S
Member
can we assume a notable increase in R as a 'loop' is metered in increments?

#10446 06/20/02 04:36 AM
Joined: May 2002
Posts: 68
E
Eandrew Offline OP
Member
Ok, here it goes:

On the roof:

mark one wire #1. Pair up two wires and label them 2,3. Pair up another two wires and label them 4,5. Mark the last wire #6.

down in the basement:

identify the two loops and label them 2,3 and 4,5. identify each of the single wires as 1,6. Now mark all your wires individually. So 1# of 1,6 and #2 of 2,3 and #3 of 2,3 and #4 of 4,5 and #5 of 4,5 and #6 of 1,6.

Now, link together 1,3,4 and then link together 2,5,6.

Back up on the roof:

#1 will have continuity w/3,4
#6 will have continuity w/2,5

untie 2,3 2 will light with 5,6 and 3 will light with 1,4

untie 4,5 4 will light with 1,3 and 5 will light with 2,6.

did I get it?

#10447 06/20/02 08:10 AM
Joined: Aug 2001
Posts: 7,520
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Member
Sorry, but if I've followed your proposal properly, it wouldn't work.

Let's see if I've understood you correctly.....

On the roof:
mark one wire #1. Pair up two wires and label them 2,3. Pair up another two wires and label them 4,5. Mark the last wire #6.

O.K., so you've positively decided upon the identification of #1 and #6 on the roof, and you have the remaining wires looped as a 2/3 pair and a 4/5 pair, and so identified. Right?

down in the basement:
identify the two loops and label them 2,3 and 4,5.

But how would you determine which is the 2/3 loop and which is the 4/5 loop? Or do you just mean at this stage to say "one of these pairs is 2/3 and the other is 4/5" ?

identify each of the single wires as 1,6.

Fine, you know that one of those open wires must be #1 and the other must be #6.


Now mark all your wires individually. So 1# of 1,6 and #2 of 2,3 and #3 of 2,3 and #4 of 4,5 and #5 of 4,5 and #6 of 1,6.


Problem: You've already decided upon the identity of #1 and #6 up on the roof. How would you know which is which in the basement in order to label them?

I can see your reasoning in the remainder of the procedure, but it's based upon a 50% chance of getting the pairs right and another 50% chance of guessing the ID of the open wires correctly.

You're kind of trying to identify the single wires using the pairs and identify the pairs using the single wires at the same time.

Starting with two looped pairs and two open wires on the roof means that you have no way to accurately identify one wire to use as a reference point while in the basement.

Back to the drawing board???7 [Linked Image]



[This message has been edited by pauluk (edited 06-20-2002).]

#10448 06/20/02 03:50 PM
Joined: Jan 2002
Posts: 2
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Junior Member
Assuming no shorts and wires are continuous.

On the roof:
Arbitrarily label one wire as #1. Tie three wires together and then tie the remaining two together.

In the basement:
Mark the wire that did not ring out as #1. Find the bundled wires and note the groups. Arbitrarily mark one of the wires in the three group as #2 and tie that to #1. Mark the second wire as #3 and leave that hanging. Mark the last wire as #4. Then take the two bundle and arbitrarily mark one of the wires as #5 and tie that with #4. Mark the last wire as #6.

On the roof:
Untie the three group. Ring out using #1 to look for #2. Ring out using the two bundle to look for #4. Remaining wire of three bundle is #3. Untie two bundle and use #4 to look for #5. Remaining wire is #6.

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