Re: A4 Car Phone

[dan_masi@MENTORG.COM (Dan Masi)]

On Jun 15,  3:42pm, Seehack@aol.com wrote:
> Subject: A4 Car Phone
> Anybody know if I can hook up an after market car phone or a
> cellular phone (e.g. Motorola, Nokia, Ericsson, ..) to the A4
> pre-wired hands-free phone system (i.e. to use the built-in
> audio mute and microphone) ?

Here's my understanding of the situation:

The A4 has an RJ45 jack below the center armrest, and a
DB-25 type connector in the trunk.  These are wired in
the "standard" Motorola way; you can plug a Motorola
transceiver unit into the trunk connector and the handset
into the RJ45 and all will work.

Non-Motorola units are not that easy.  The built-in
microphone isn't just a microphone; there's an active
preamp at the mic.

I already had an AT&T 6650 cellphone (Nokia 2120), and
for Christmas I got the matching handsfree kit for the
car, so I'm about to install the kit into my A4Q.  I'm
going to mount it in the area just beneath the center
armrest.  I'll be removing the Motorola mike from behind
the A-pillar and putting the one that came with the handsfree
kit there.

My handsfree kit doesn't provide a radio mute output, so
I'll be tinkering with it to generate one.  For the
electronically-inclined here:  I figure I'll
basically put an op-amp across the kit's speaker and feed
it to a "one-shot"... that way, whenever something is sounding
on the speaker, I'll get a mute output, and the output will
stay active for, say, 20-30 seconds after.  Anyone know what
kind of signal the radio is expecting for MUTE, and on
what pin of the Motorola 25-pin connector it appears?

Dan Masi