I said I'd never blogSmall introduction
You may not be familiar with the variety of the different kinds of phone plugs you may find, even just in Europe. I was a bit familiar with the French one (for which the Wikipedia page has room for improvement), for which the addition of extra phones can't be easier:
| filter additional and so
| plug on...
| __ __ __
[ =| [ =| [ =| [
wall [ =| [ =| [ =| [
[ =| [ =| [ =| [
| |__| |__| |__|
|
| ^ ^ ^
| DSL RJ-11 or RJ-11 or
| phone phone
These plugs have 6 (six) pins, of which only two are used (called A and B). Additional plugs are added as shown, each one gently proxying the wall plug to the next. This can easily stack up to 10 centimeters (4 inches) off the wall though.
Where it gets trickier
I am currently staying in Germany, and of course they have a different system. Even though the German one looks just like a smaller version of the French, it gave me a hard time:
- the A and B wires are on different pins (including on the equivalent RJ-11 pinout)
- I had French phones and modems only
- German manufacturers tend to sell moulded plugs only
- regular plugs cannot be chained
My first issue was with the DSL modem. The German providers send a DSL filter that looks just like a regular wall socket:
__________ | | | || || || | < TAE N, TAE F, TAE N | || || || | | | |__________| ^ ^ from the to the wall modem
I logically needed an RJ-11 cable that would cross pins 1-2 and 3-4 from the RJ-11 plug. For some reason this did not work (different DSL standard?), and I obtained an old modem from a friend.
Single phone
At this point I had Internet working, but I needed a TAE-to-RJ11 adapter, and for the reason stated above, nobody had spares. So I went to one of the major electronic shops around here, and looked at the prices for such a thing. I kid you not, it was more expensive to obtain a single one than to buy a 6-meter cord extension with a choice of TAE-N or TAE-F connector.
Even so, the adapters looked really poor, factored in a dirt cheap, fragile plastic casing. The great thing though, was that I could open and re-wire it! So I simply inverted pins 1 with 2, and 3 with 4 again, and it worked.
Second phone or modem
Finally, I wanted to hook up an additional phone. I also still had a POTS modem that I wanted to put to good use, as a fax machine eventually. The issue was that as soon as I added any kind of additional plug, it would work but block the regular one.
My first reaction was to get an extra DECT handset. But I don't give up so easily.
After lots of readings of forums (duh), DSL filter schematics (ouch), and tests, there was still no way I could make it work. Even using the right-most plugs and additional A and B wire pairs would not let me connect the two devices at the same time.
The solution
Then I realized with a multimeter that the 3 and 4, 2 and 5, and 1 and 6 pairs are actually connected when no plug is present, but disconnected as soon as there is one. Moreover, the three TAE plugs are chained likewise internally, so disconnecting one isolates the others.
Consequently, as the Wikipedia page mentions, I realized that it is actually up to the devices to chain them when connected. My devices were obviously not doing it, since they only use the French A and B wires (the others are not even present). Therefore, all I had to do is to add two pieces of wire in my RJ-11 adapter, to bridge pins 3 to 4 and 2 to 5.
And it worked.
