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I tried to make this as thorough as possible. I have a 4p4c socket + cable here. As there is no manual for german wiring I had to measure each wire against each other wire while hearing the "ready to dial" tone to find it out, but I am still clueless.

This is what I got

  • 12--0.4V-DC
  • 13--4.2V-DC
  • 14--0.2V-DC
  • 21-0.37V-DC
  • 23-0V-AC
  • 24-0.1V-DC
  • 31-0.4V-DC
  • 32-0.001V-DC
  • 34-0.2V-DC
  • 41-0.2V-DC
  • 42-0V-DC
  • 43--0.2V-DC

Explaination:

  • 1 means white
  • 2 green
  • 3 yellow
  • 4 brown
  • First number is one of the colors I put the mass of my oscilloscope to.
  • Second number is the color/wire I put the signal of my oscilloscope to.
  • one "-" is meant for separation
  • Then the value follows
  • Then the unit follows
  • one "-" is meant for separation
  • then there is the type of voltage/current measured

So for instance 

43--192mV-DC means GND to brown, signal to yellow, result: -192mV, type of voltage/current measured: DC

or

42-5.7mv-AC means GND to brown, signal to green, result: 5.7mV, type of voltage/current measured: AC

Please tell me, which cable go to speaker and which to microphone. Also, do I need additional circuitry? In the english wikipedia there is a 500 ohms resistor. Do I need this, what is it for and where to put it?

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1 Answer 1

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UPDATE:

On rereading it's not obvious where you are connecting this or what it is you are connecting.

If this is a headset cord (as it seems to be) then what I said about voltages is wrong.

What are you connecting to what?

OLDER:

Nothing makes sense.

If this is to a "central Office" you should have 50V DC somewhere.
If to a PBX possibly 25 VDC or lower.

1,3 = 4.2V and 3,1 = 395 mV suggests that you are grounding the signal with your scope ground in the second case. You need a differential probe or isolated scope or measurements relative to ground.

Connecting ground to one wire will unbalance a feed circuit and allow induced noise from all over. Balanced load or feed must be used.

Use a magnetic earpiece of around 1000 Ohms or a high impedance one with a say 470 Ohm resistor across it. Connect to 2 wires at a time and listen for dial tone. Go from there.

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  • \$\begingroup\$ Thanks. I am going to try kalshagar.wikispaces.com/Cisco+IP+phone+headphone which I just found. \$\endgroup\$ Commented Oct 10, 2012 at 1:01
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    \$\begingroup\$ "What are you connecting to what?" I am connecting a telephone cord to a telephone which in turn is connected to my telephone provider. I am picking up the phone so I get the "ready to dial"-tone but of course I cannot hear that because I connected my own handset cord to it of which the ending is being cut so I get the bare wires. There I measured the voltages with an oscilloscope and chose AC or DC based on what made sense. BTW: How can I be notified if someone replies here? \$\endgroup\$ Commented Oct 10, 2012 at 3:08
  • \$\begingroup\$ I found kalshagar.wikispaces.com/Cisco+IP+phone+headphone to not be true. \$\endgroup\$ Commented Oct 10, 2012 at 4:57

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