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


  • 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



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




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?



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?


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\$ – Zurechtweiser Oct 10 '12 at 1:01
  • 1
    \$\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\$ – Zurechtweiser Oct 10 '12 at 3:08
  • \$\begingroup\$ I found kalshagar.wikispaces.com/Cisco+IP+phone+headphone to not be true. \$\endgroup\$ – Zurechtweiser Oct 10 '12 at 4:57

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