Trying to use induction before I drive a screw ??

[jalbers@bsu.edu]

I am trying to locate hidden 110V and 220V wires behind residential
walls. I know that I could just throw some money at it and buy a
commercial locator but what would be the fun in that? Besides, I
played with someone's $100 tone generator/probe combination a few
years ago and it worked great for tracing CAT5 cables at the punch
down pannel but didn't work very well at all for finding CAT5 cable
inside of walls.

I have done some experimenting with a 6" coil of copper wire with
about 200 turns of magnet wire connected to a 741 op amp (non-
inverting configuration, closed loop gain set to 1000, dual 9V supply)
with the output connected to a pair of cheap headphones. I can find
big things like the back side of a circuit breaker pannel, electric
motors, wall warts, or the back side of the power meter. If I get
real close to an outlet box or switch box I can pick up a 60Hz tone.
However, I cannot reliably find any wires inside of the wall even if
they are carying some current.

How can I improve apon this type of circuit or is there a better
homemade way of doing this? Hall effect sensors for example??

Any help would be greatly apprediated. Thanks

 

[Sjouke Burry]

jalbers@bsu.edu wrote:

I am trying to locate hidden 110V and 220V wires behind residential
walls. I know that I could just throw some money at it and buy a
commercial locator but what would be the fun in that? Besides, I
played with someone's $100 tone generator/probe combination a few
years ago and it worked great for tracing CAT5 cables at the punch
down pannel but didn't work very well at all for finding CAT5 cable
inside of walls.

I have done some experimenting with a 6" coil of copper wire with
about 200 turns of magnet wire connected to a 741 op amp (non-
inverting configuration, closed loop gain set to 1000, dual 9V supply)
with the output connected to a pair of cheap headphones. I can find
big things like the back side of a circuit breaker pannel, electric
motors, wall warts, or the back side of the power meter. If I get
real close to an outlet box or switch box I can pick up a 60Hz tone.
However, I cannot reliably find any wires inside of the wall even if
they are carying some current.

How can I improve apon this type of circuit or is there a better
homemade way of doing this? Hall effect sensors for example??

Any help would be greatly apprediated. Thanks

I would ad a capacitive pickup right to the centre of your

pickup coil,add another 741 1000 times amplifier, put 2 diodes
(total 4) across each input to limit things somewhat, and use
this combination to scan the walls.

 

[Sjouke Burry]

jalbers@bsu.edu wrote:

On Sep 2, 3:50 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnlll
wrote:
jalb...@bsu.edu wrote:
I am trying to locate hidden 110V and 220V wires behind residential
walls. I know that I could just throw some money at it and buy a
commercial locator but what would be the fun in that? Besides, I
played with someone's $100 tone generator/probe combination a few
years ago and it worked great for tracing CAT5 cables at the punch
down pannel but didn't work very well at all for finding CAT5 cable
inside of walls.
I have done some experimenting with a 6" coil of copper wire with
about 200 turns of magnet wire connected to a 741 op amp (non-
inverting configuration, closed loop gain set to 1000, dual 9V supply)
with the output connected to a pair of cheap headphones. I can find
big things like the back side of a circuit breaker pannel, electric
motors, wall warts, or the back side of the power meter. If I get
real close to an outlet box or switch box I can pick up a 60Hz tone.
However, I cannot reliably find any wires inside of the wall even if
they are carying some current.
How can I improve apon this type of circuit or is there a better
homemade way of doing this? Hall effect sensors for example??
Any help would be greatly apprediated. Thanks
I would ad a capacitive pickup right to the centre of your
pickup coil,add another 741 1000 times amplifier, put 2 diodes
(total 4) across each input to limit things somewhat, and use
this combination to scan the walls.- Hide quoted text -

- Show quoted text -

Thanks
I don't know anything about capacitive pickups so I have lots of
strange questions. Can they be built or taken out of something cheap,
or must they be purchased? I think that some microphones for example
are based on a capacitance pickup. How exactly is capacitance used in
this application? Are we trying to make a capacitor by using one of
the wires (ground wire for example) as one of the plates of a
capacitor and a metal plate outside of the wall as the other?

Just a 2 by 2 inch metal plate, connected to the centre wire

of a shielded cable running to the + imput of the amplifier,
which is then connected to ground with a 2 megohm resistor.
The same effect as when your finger gets close to a sensitive
audio input, where you start to hear a 50/60 hz hum.
Keep the shielded cable short, because it degrades sensitivity,
although you need it to keep pickup confined to the metal plate
area.

 

[jalbers@bsu.edu]

On Sep 2, 3:50 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnlll>
wrote:

jalb...@bsu.edu wrote:
I am trying to locate hidden 110V and 220V wires behind residential
walls.  I know that I could just throw some money at it and buy a
commercial locator but what would be the fun in that?  Besides, I
played with someone's $100 tone generator/probe combination a few
years ago and it worked great for tracing CAT5 cables at the punch
down pannel but didn't work very well at all for finding CAT5 cable
inside of walls.

I have done some experimenting with a 6" coil of copper wire with
about 200 turns of magnet wire connected to a 741 op amp (non-
inverting configuration, closed loop gain set to 1000, dual 9V supply)
with the output connected to a pair of cheap headphones.  I can find
big things like the back side of a circuit breaker pannel, electric
motors, wall warts, or the back side of the power meter.  If I get
real close to an outlet box or switch box I can pick up a 60Hz tone.
However, I cannot reliably find any wires inside of the wall even if
they are carying some current.

How can I improve apon this type of circuit or is there a better
homemade way of doing this?  Hall effect sensors for example??

Any help would be greatly apprediated.  Thanks

I would ad a capacitive pickup right to the centre of your
pickup coil,add another 741 1000 times amplifier, put 2 diodes
(total 4) across each input to limit things somewhat, and use
this combination to scan the walls.- Hide quoted text -

- Show quoted text -

Thanks
I don't know anything about capacitive pickups so I have lots of
strange questions. Can they be built or taken out of something cheap,
or must they be purchased? I think that some microphones for example
are based on a capacitance pickup. How exactly is capacitance used in
this application? Are we trying to make a capacitor by using one of
the wires (ground wire for example) as one of the plates of a
capacitor and a metal plate outside of the wall as the other?

 

[Jasen Betts]

On 2008-09-02, jalbers@bsu.edu <jalbers@bsu.edu> wrote:

I am trying to locate hidden 110V and 220V wires behind residential
walls.

plug a cheap CFL into one of the outlets on the branch you are trying
to trace, that should increase the noise level.

Bye.
Jasen