Telephone "in use" indicator

[Earl]

I want to build a telephone in-use indicator from a diagram
I found on an electronics website. In the diagram two wires
from the telephone are connected to the circuit. However,
I clearly remember that telephone cables have more than just
2 wires inside them. How would I know which ones to use?

 

[Michael A. Terrell]

I want to build a telephone in-use indicator from a diagram
I found on an electronics website. In the diagram two wires
from the telephone are connected to the circuit. However,
I clearly remember that telephone cables have more than just
2 wires inside them. How would I know which ones to use?

I don't know about the UK, but in the US we use the red and green
wires for a single line telephone. The yellow and black are for a second
line, or on very old "princess" telephones that had low voltage AC to
power the lighted dial.

Newer, three pair, phone wire uses the blue/white pair for line one.

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We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida

 

[CapMan]

Some phone cables do have more but only 2 are needed. The tip and ring...

 

[Earl]

I don't know about the UK, but in the US we use the red and green

wires for a single line telephone. The yellow and black are for a second
line, or on very old "princess" telephones that had low voltage AC to
power the lighted dial.

Newer, three pair, phone wire uses the blue/white pair for line one.

I have just opned an old phone I had in the attick. It seems to have the
following wires, with letters where they connect to the circuit board,
as follows:

E green
b red
s blue
a white

Strangely, the E is in upper case and the others are in low case
any ideas what I need to use ?

btw. it is a pulse phone, about 15 years old.

 

[cpemma]

I want to build a telephone in-use indicator from a diagram
I found on an electronics website. In the diagram two wires
from the telephone are connected to the circuit. However,
I clearly remember that telephone cables have more than just
2 wires inside them. How would I know which ones to use?

If you're in the UK I'd be wary of connecting a home-built 'net circuit to
the line,

(a) it's against BT terms & conditions - affect the line & you're in
trouble,

(b) the UK phone voltages are quite different to the US levels which your
circuit may be designed for.

If you must do it, at least find a UK-specific circuit.

 

[Earl]

(a) it's against BT terms & conditions - affect the line & you're in

trouble,

(b) the UK phone voltages are quite different to the US levels which your
circuit may be designed for.

If you must do it, at least find a UK-specific circuit.

I'll give you the link and you can judge for yourself if this circuit is
safe:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#inuse.gif

Regarding a. I suspect this exists in all countries. Regarding b. can you
please
describe the voltage differences, and suggest circuit modifications if
needed.

tia.

 

[cpemma]

I'll give you the link and you can judge for yourself if this circuit
is safe:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#inuse.gif

Regarding a. I suspect this exists in all countries. Regarding b. can
you please
describe the voltage differences, and suggest circuit modifications if
needed.

Once past the master socket, we use a 3-wire system with a "bell" wire, and
48v DC between the other 2 (off-line), 5-10v (in use) which correspond to
ring & tip, see http://www.diyha.co.uk/telephones/pots.html for wiring
details. I've seen figures putting the ring signal at 80v AC

I can't remember the US figures, but a google groups search should turn them
up and perhaps a UK-specific circuit.

 

[Dbowey]

Earl posted:
<<
I'll give you the link and you can judge for yourself if this circuit is
safe:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#inuse.gif >>


The DC Ringer Equivalent is about 4, so I would have problems with the circuit
if used in the U.S. I'm not up-to-date on the UK requirements.

I didn't calculate the leakage current from the DC voltage running the device,
back to the tel. line, but in the U.S. absolutely NO voltage is permitted to be
placed on the line from customer equipment (for loop-start lines, which this
is).

Don

 

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

I want to build a telephone in-use indicator from a diagram
I found on an electronics website. In the diagram two wires
from the telephone are connected to the circuit. However,
I clearly remember that telephone cables have more than just
2 wires inside them. How would I know which ones to use?

It's the green and red wires, or the white with a blue stripe and blue
with a white stripe.

Here's the URL of the schematic below of the indicator you *should*
use. If you use one that doesn't have a battery but sucks power from
the line itself, the telephone company may find the line tests bad
when they do their periodic tests. If so, they may send out a
repairman, and when they find it's your equipment causing the problem,
they may bill you for the time. So don't use a line powered
indicator.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#inuse.
gif

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###Got a Question about ELECTRONICS? Check HERE First:###
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Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
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[Earl]

It's the green and red wires, or the white with a blue stripe and blue

with a white stripe.

i.e. E and b

Here's the URL of the schematic below of the indicator you *should*
use. If you use one that doesn't have a battery but sucks power from
the line itself, the telephone company may find the line tests bad
when they do their periodic tests. If so, they may send out a
repairman, and when they find it's your equipment causing the problem,
they may bill you for the time. So don't use a line powered
indicator.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#inuse.
gif

how does it work ? what is the reason for C=0.1uf

 

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

i.e. E and b

how does it work ? what is the reason for C=0.1uf

How? Well, simplified, the transistor requires a voltage of less than
about 3V to conduct and light the LED. The three resistor voltage
divider puts more than 3V across the 680k when the phone is on hook,
and the voltage drops below 3V when the phone is off hook, and the LED
lights up.

You could also look at it as a current summing point at the junction
of the transistor's base and the 680k. When the current from the
phone line is equal to or greater than the current thru the 680k, the
base sees no forward bias and the LED stays off. When the current is
less than the current thru the 680k, that current from the 680k
forward biases the transistor and the LED lights.

And yes, you have to take into account the .6V drop across the base to
emitter junction.

The 0.1 uF is to filter out RFI or other noise, even ringing current,
from the phone line, so all you see is the DC voltage.


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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
@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@