Using signal generation to detect the location of a line break in my wall

[Eric Livingston]

I have three speaker wires running just behind sheetrock along a wall in my
house that have breaks in them somewhere (I believe from the contractor
firing nails through the wires when putting up the sheetrock). Two of the
wires are shorted from one end (wall terminal) and open from the other. The
third is open from both ends. I figure in all cases a nail-gunned nail went
through the wire in question, and in two cases the nail is probably shorting
one half of the wire.

I would like to detect where the breaks are in the wall.

I've tried generating emf in the shorted lines in the wall using a strong
magnet, and it works to a degree but not enough - I need a stronger magnet
or a more sensitive multimeter.

What I'm thinking now is that if I can use the wire(s) in the wall as an
antenna, generating some kind of signal, I could use a receiver held up to
the wall to detect that signal, and thus detect the break. Would this work?
How would I best do this?

Also, I've used a small electric motor as a generator to create an AC
current in the wires. This also works to a small degree even with the cut
(i.e. open) wires in the walls due to the capacitance of the wire, though
there's no closed circuit. Can I use something to detect the AC Current in
the wires behind the wall? Could this work even with the broken (not
shorted) wires, relying on nothing but the wire capacitance to allow a
trickle of AC current to get through?

Are there other ways to do what I'm trying to do? It seems like it should be
possible.

Thanks,
Eric

 

[Rein Wiehler]

I have three speaker wires running just behind sheetrock along a wall
in my house that have breaks in them somewhere (I believe from the
contractor firing nails through the wires when putting up the
sheetrock). Two of the wires are shorted from one end (wall terminal)
and open from the other. The third is open from both ends. I figure
in all cases a nail-gunned nail went through the wire in question,
and in two cases the nail is probably shorting one half of the wire.

I would like to detect where the breaks are in the wall.

I've tried generating emf in the shorted lines in the wall using a
strong magnet, and it works to a degree but not enough - I need a
stronger magnet or a more sensitive multimeter.

What I'm thinking now is that if I can use the wire(s) in the wall as
an antenna, generating some kind of signal, I could use a receiver
held up to the wall to detect that signal, and thus detect the break.
Would this work? How would I best do this?

Also, I've used a small electric motor as a generator to create an AC
current in the wires. This also works to a small degree even with the
cut (i.e. open) wires in the walls due to the capacitance of the
wire, though there's no closed circuit. Can I use something to detect
the AC Current in the wires behind the wall? Could this work even
with the broken (not shorted) wires, relying on nothing but the wire
capacitance to allow a trickle of AC current to get through?

Are there other ways to do what I'm trying to do? It seems like it
should be possible.

Thanks,
Eric

yes its possible - but what are you going to do once you locate the
wires? dig holes in the wall?
rw

 

[James Sweet]

yes its possible - but what are you going to do once you locate the
wires? dig holes in the wall?
rw

He'll have to, but it's better than having to tear into the wall along the
entire length of the cable.

 

[Eric Livingston]

He'll have to, but it's better than having to tear into the wall along the
entire length of the cable.

Right - I'll certainly have to punch through the wall to fix the break - but
that's just a single easily patched hole vs. ripping out a wall (which,
frankly, I won't do as it's not worth it).

If I can isolate the break, I can easily get through the wall to fix it. I
just need to find the break

 

[Wim Ton]

I have three speaker wires running just behind sheetrock along a wall in
my

house that have breaks in them somewhere (I believe from the contractor
firing nails through the wires when putting up the sheetrock). Two of the

One possibilty is Time Domain Reflectometry (TDR)

Connect an oscilloscope and a pulse-generator ( with needle like pulses) to
the suspect wire and ensure it is terminated with the characteristic
impedance on both ends, something like 100 ohm for twisted pair.On the
oscilloscope you will see the pulse and a reflection at the short of open.
The speed of the signal in a cable is about 2/3 of the speed of light
(calibrate with a known piece of cable) so the fault will be at 0.5 (because
the signal has to go back and forth) * time / speed. Do not expect
millimeter accuracy, so you may still have to hack a long hole in the wall
:-(

Succes, Wim

 

[Genome]

"Eric Livingston" <[email protected]> went bleat in message

And cross posted it all over the shop.

This post comes from the design group. I am not representative but this is
where I spout my venom.

Kindly **** off and lay some new speaker wires for your lo-fi under the
carpet.

It's certainly not my arse problem that you don't have the basic sensibility
in your head to realise that you had the wires in the first place and
couldn't tell your fuey schung 'architeks' about the situation.

As if you had the original installers do it properly in the first place

Try

..it

And don't bint about the fact it doesn't exist.

Kindest regards

DNA

 

[Paul Landregan]

I have three speaker wires running just behind sheetrock along a wall in my
house that have breaks in them somewhere (I believe from the contractor
firing nails through the wires when putting up the sheetrock). Two of the
wires are shorted from one end (wall terminal) and open from the other. The
third is open from both ends. I figure in all cases a nail-gunned nail went
through the wire in question, and in two cases the nail is probably shorting
one half of the wire.

I would like to detect where the breaks are in the wall.

I've tried generating emf in the shorted lines in the wall using a strong
magnet, and it works to a degree but not enough - I need a stronger magnet
or a more sensitive multimeter.

What I'm thinking now is that if I can use the wire(s) in the wall as an
antenna, generating some kind of signal, I could use a receiver held up to
the wall to detect that signal, and thus detect the break. Would this work?
How would I best do this?

Also, I've used a small electric motor as a generator to create an AC
current in the wires. This also works to a small degree even with the cut
(i.e. open) wires in the walls due to the capacitance of the wire, though
there's no closed circuit. Can I use something to detect the AC Current in
the wires behind the wall? Could this work even with the broken (not
shorted) wires, relying on nothing but the wire capacitance to allow a
trickle of AC current to get through?

Are there other ways to do what I'm trying to do? It seems like it should be
possible.

Thanks,
Eric

You could try a telephonce cable pair identifyer. The transmit a warbline
tone which is picked up with a reciever. You follow the cable tehn at the
open there will be a peak in signal then nothing afterwards.

 

[Genome]

"Eric Livingston" <[email protected]> went bleat in message

And cross posted it all over the shop.

This post comes from the design group. I am not representative but this is
where I spout my venom.

Kindly **** off and lay some new speaker wires for your lo-fi under the
carpet.

It's certainly not my arse problem that you don't have the basic sensibility
in your head to realise that you had the wires in the first place and
couldn't tell your fuey schung 'architeks' about the situation.

As if you had the original installers do it properly in the first place.

Try

ed.it

or


or


And don't bint about the fact they don't exist.

See, we design people design things. Unfortunately we have to deal with the
crass stupidity of people like you and yours. It and you ain't fucking worth
it.

Kindest regards

DNA

 

[John Fields]

I have three speaker wires running just behind sheetrock along a wall in my
house that have breaks in them somewhere (I believe from the contractor
firing nails through the wires when putting up the sheetrock). Two of the
wires are shorted from one end (wall terminal) and open from the other. The
third is open from both ends. I figure in all cases a nail-gunned nail went
through the wire in question, and in two cases the nail is probably shorting
one half of the wire.

I would like to detect where the breaks are in the wall.

I've tried generating emf in the shorted lines in the wall using a strong
magnet, and it works to a degree but not enough - I need a stronger magnet
or a more sensitive multimeter.

What I'm thinking now is that if I can use the wire(s) in the wall as an
antenna, generating some kind of signal, I could use a receiver held up to
the wall to detect that signal, and thus detect the break. Would this work?
How would I best do this?

Also, I've used a small electric motor as a generator to create an AC
current in the wires. This also works to a small degree even with the cut
(i.e. open) wires in the walls due to the capacitance of the wire, though
there's no closed circuit. Can I use something to detect the AC Current in
the wires behind the wall? Could this work even with the broken (not
shorted) wires, relying on nothing but the wire capacitance to allow a
trickle of AC current to get through?

Are there other ways to do what I'm trying to do? It seems like it should be
possible.

For the wires that are shorted, if the nail is what's causing the short
you could check for continuity from the shorted end to the nails by
tying an ohmmeter to the end of the wire and probing the suspect
nailheads with a needle connected to the other ohmmeter lead. Find the
nailheads with a magnetic stud finder.

For the wire that's open on both ends, if you can just pull one end out
from behind the wall you'll know how long it is once you get it pulled
out and you'll know about where the break is (in X, anyway). Along
those lines, if you can pull on one of the wires and the other end moves
you might be able to use that wire to pull three new ones and forget
about having to damage the wall.

 

[mike]

I have three speaker wires running just behind sheetrock along a wall in my
house that have breaks in them somewhere (I believe from the contractor
firing nails through the wires when putting up the sheetrock). Two of the
wires are shorted from one end (wall terminal) and open from the other. The
third is open from both ends. I figure in all cases a nail-gunned nail went
through the wire in question, and in two cases the nail is probably shorting
one half of the wire.

I would like to detect where the breaks are in the wall.

I've tried generating emf in the shorted lines in the wall using a strong
magnet, and it works to a degree but not enough - I need a stronger magnet
or a more sensitive multimeter.

What I'm thinking now is that if I can use the wire(s) in the wall as an
antenna, generating some kind of signal, I could use a receiver held up to
the wall to detect that signal, and thus detect the break. Would this work?
How would I best do this?

Also, I've used a small electric motor as a generator to create an AC
current in the wires. This also works to a small degree even with the cut
(i.e. open) wires in the walls due to the capacitance of the wire, though
there's no closed circuit. Can I use something to detect the AC Current in
the wires behind the wall? Could this work even with the broken (not
shorted) wires, relying on nothing but the wire capacitance to allow a
trickle of AC current to get through?

Are there other ways to do what I'm trying to do? It seems like it should be
possible.

Thanks,
Eric

I'd vote for TDR. Know anybody who works for the cable company or the
phone company?

They make gizmos for finding hot power wires in the wall. Can get 'em
at any home depot. I'm guessing they just pick up the hum.
Don't know how much AC voltage you'd have to put on
your speaker wires to be detcted or whether that would be safe. You can
also
get fire extinguishers at home depot ;-)
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
Honda CB-125S
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Watson A.Name - Watt Sun, Dark Remover]

I have three speaker wires running just behind sheetrock along a wall in my
house that have breaks in them somewhere (I believe from the contractor
firing nails through the wires when putting up the sheetrock). Two of the
wires are shorted from one end (wall terminal) and open from the other. The
third is open from both ends. I figure in all cases a nail-gunned nail went
through the wire in question, and in two cases the nail is probably shorting
one half of the wire.

I would like to detect where the breaks are in the wall.

I've tried generating emf in the shorted lines in the wall using a strong
magnet, and it works to a degree but not enough - I need a stronger magnet
or a more sensitive multimeter.

What I'm thinking now is that if I can use the wire(s) in the wall as an
antenna, generating some kind of signal, I could use a receiver held up to
the wall to detect that signal, and thus detect the break. Would this work?
How would I best do this?

Also, I've used a small electric motor as a generator to create an AC
current in the wires. This also works to a small degree even with the cut
(i.e. open) wires in the walls due to the capacitance of the wire, though
there's no closed circuit. Can I use something to detect the AC Current in
the wires behind the wall? Could this work even with the broken (not
shorted) wires, relying on nothing but the wire capacitance to allow a
trickle of AC current to get through?

Are there other ways to do what I'm trying to do? It seems like it should be
possible.

A cable testing meter that has TDR, such as the Fluke DSP-2000 can
tell you where the break is, bow many feet from the end. Cat5 cable
installers use these, and they can be rented. For more cable info try
the comp.dcom.cabling newsgroup.

Thanks,
Eric

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[Watson A.Name - Watt Sun, Dark Remover]

yes its possible - but what are you going to do once you locate the
wires? dig holes in the wall?
rw

That's what people usually do. Cut a hole, and patch it after the
repair.

--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Eric Livingston]

Are there other ways to do what I'm trying to do? It seems like it
should

be
You could try a telephonce cable pair identifyer. The transmit a warbline
tone which is picked up with a reciever. You follow the cable tehn at the
open there will be a peak in signal then nothing afterwards.

Does the cable pair identifier have to have a closed circuit to work? If so
it might work with the two shorted lines, but wouldn't with the one that's
just cut. If it would work with the cut one as well that would be a perfect
solution! I'll look into those.

Thanks!

 

[Eric Livingston]

the

One possibilty is Time Domain Reflectometry (TDR)

Succes, Wim

I've looked into this - the only real problem I have is I can't reliably
know how the cable pays out behind the wall - i.e. if I were to figure out
that the break is 10' along the cable, I can't really figure out where the
tenth foot is behind the wall. The cable takes too many turns and is routed
around things.

 

[Eric Livingston]

For the wires that are shorted, if the nail is what's causing the short

you could check for continuity from the shorted end to the nails by
tying an ohmmeter to the end of the wire and probing the suspect
nailheads with a needle connected to the other ohmmeter lead. Find the
nailheads with a magnetic stud finder.

I had thought about doing just that, but the stud finder I have doesn't
differentiate between metal and wood, so I can't isolate the nail heads. I
guess from your post there are stud finders that can find just metal, and
ignore wood?

For the wire that's open on both ends, if you can just pull one end out
from behind the wall you'll know how long it is once you get it pulled
out and you'll know about where the break is (in X, anyway). Along
those lines, if you can pull on one of the wires and the other end moves
you might be able to use that wire to pull three new ones and forget
about having to damage the wall.

Unfortunately, the wires are stapled into place and routed around things in
the wall, so I can't pull them out.

 

[Eric Livingston]

Are there other ways to do what I'm trying to do? It seems like it
should be

A cable testing meter that has TDR, such as the Fluke DSP-2000 can
tell you where the break is, bow many feet from the end. Cat5 cable
installers use these, and they can be rented. For more cable info try
the comp.dcom.cabling newsgroup.

Thanks! I'll try over there. The TDR solution may help some - at least to
get a ballpark. The trouble is I can't know, for instance, where the 10th
foot of cable is behind the wall too accurately. The cable routes around
things in the wall and isn't on a straight route. But it would help to know
whether the break is 2 feet or 18 feet along the run, certainly.

 

[red]

There are devices that will tell you how long a cble is and can tell you
where shorts are. Pretty accurate, but expensive.

BEST ADVICE YET::

Don't tear a hole in the wall. At one end of the cable tightly tie on some
new cable, and at the other end pull the old cable though until you have
brand new wire in the wall. No wall repair required

 

[GPG]

Try a digital meter with a good capacitance range, calibrate on a
piece of cable. Measure the O/C ends and calculate distance. As a test
I measured
about 3.5 M of cable and got 180pF or about 50pF/M.

 

[CWatters]

If you don't mind a drop in audio quality.....

Perhaps you could get by with a common earth return? eg....

Three speakers need only 4 wires (not 6).

Two speakers need only 3 wires.

Prerhaps you have enough working wires to get something going?

Colin

 

[James Sweet]

There are devices that will tell you how long a cble is and can tell you
where shorts are. Pretty accurate, but expensive.

BEST ADVICE YET::

Don't tear a hole in the wall. At one end of the cable tightly tie on some
new cable, and at the other end pull the old cable though until you have
brand new wire in the wall. No wall repair required

Cables are usually stapled in multiple places, it's unlikely that a new one
would pull through. Conduit would be ideal but is rarely used in residences.