NAVNF + - How does it work
 

So this is a techy one, how does the radio know when to mute/merge the audio from the NAVNF pins? A signal on NAVBUS or does it detect the hiss/bong/impedence change on the NAVNF lines?

/me prods Jochen in the ribs

They work in slightly different ways.

The mute is done via a pin pull down (to GND) on the mute pin (not i-bus), the audio mix is a bit more complicated mate.

When using it for phone;

The radio mutes (as normal) and then (**I think**), the TEL-ON is sent high (+12v), this switches the input source form onboard to the TEL/Nav inputs (the telephone takes priority), what this does (in effect) is allow external input to the radio to pass through and be amped by the system and pass to the speakers (fronts only).

It's the TEL-ON that allows the input into the system, if this stays down then no audio output (full mute).

If this stays up (for any reason) then you can hear a hiss in the background.

I only found this out when making up the retrofit BT looms mate, when making one you need both mute and tel-on.

I tried it without the tel-on and if you use a telemute then it does work (as you don't pass the phone into the radio), if you direct inject the BT into the radio and don't use tel-on then you get no sound from the phone kit (OEM or AM).

I did a mock up for injecting a BT A2DP clip audio source into the OEM radio's BT inputs and it does work, but you need mute and tel-on.

The Sound was not that great as it was mono, but I just wanted to prove the concept.

You may need to check the mute and tel-on signals (high or low) as it was a while since I did this and I could have them the wrong way round.

Course, I could be talking out my hat.

I'm not 100% sure how the nav audio works with the system TBH, but it **could** be a similar setup, It could also be done internally (radio or nav), its a guess.

Jochen will probably know mate.

Jochen is probably stuffing his face with cookies right now (inside joke).

MUTE is indeed active low and TELON active high, but they are only for the phone. The nav computer does not have a connection to TELON on the harness.

Looking at the wiring diagram, it seems the TV Tuner is also using NAVNF for audio, would I be right in sayng the TV can create audio while you browse the menus? In that case maybe it does work on detecting audio, as NAVBUS does seem to bypass the video module.

OK.

Indeed.

Yes, I think so, I'd need to double check that.

The TV has it's own audio in to the radio.

At a guess, I's say that the nav has a permanent (internal) bridge within the radio and when the nav outputs a signal (a voice command), then its just piggybacks the audio, the amount of "mix" is set-able via the set menu and this must have a similar effect as a reostat on the (mute).

hmmm, just a thought, I wonder if one could pipe an audio source directly using the nav input pins (in the smaller 12 pin block), and see if that piggybacks the normal audio???