Hello all,

I've been working on an interface to the phone line for my PIC projects.
After several nights of reading on the internet about interfacing to the
telephone lines, I have learned much.  I've also come to the conclusion,
that the simplest/cheapest solution for me now would probably be to use this
board from a telephone I hacked up.

This base unit circuit board has TA31002P ringer ic on it, with almost the
exact same circuit as that chips datasheet.  I've decided to use this board
since it has all the stuff for ring detection right on it, and I can use the
leads that run the ringer speaker as an input (with a few other components
maybe) to my microcontroller.

My question is in regards to the 4 wires that run to the handset (through
the pigtail-type cable).  I've done some poking around with the multimeter
and these lines have a small voltage on them, which varies when I talk into
another phone in my apartment.  It would seem to me that these are the
microphone and speakers for the handset.  It appears like the speaker is
Red(+) and Green(-), and the microphone is Yellow(+) and Black(-).  Does
anyone know this to be true?  Is this standard?  The wires are labeled A to
D on the circuit boards, and on the handset and the base circuit board, the
green wire isn't connected to anything.

On the handset circuit board, it looks like the yellow wire and the black
wire (and one other signal that goes the tone generator chip) is connected
to the hook switch.  How are these signals used for the hook switch?  Would
shorting out the yellow and black wires cause my phone to be "on-hook" or
vice versa?

One last question, where do the chips on the handset circuit board get power
from if the only 4 wires connected to it are audio signals?

I wish I could find more information on the chips on the handset circuit
board so I could use the tone generator and another chip that's on there.
But without finding the datasheets, I'm kinda lost.

Any help anyone could offer to shed some light on what these four wires
(black,red,green,yellow) are for and how I could use them for
hanging/picking up the phone line, sending tones into, getting audio out of,
etc.. would be much appreciated.

P.S.  Just to clarify, I'm not referring to the actual telephone lines at
all, but rather the 4 wires that go from the telephones base unit through
the pigtail cord into the telephone handset.

Thanks in advance to any replies.

MJ Brush

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