Stereo Mute timer?

[Swifty]

Hi there,
I'm trying to build a car kit for my mobile phone, I have got the pinout's for the phone so that I can hook this up to my stereo's inputs, but I need the stereo to mute when on the phone.
The stereo has a telephone mute wire, which I believe mutes the unit when grounded, but I haven't yet had chance to check.
The problem is I need some sort of a timer that can be activated by the audio signal from the phone becoming live, and that starts counting when the signal is lost, for say.. 3 seconds or so.
Because I am going to try taking the telephone mute signal from the audio output on the phone (as there is no proper connector for this)
If I didn't have a timer I think that the stereo would keep cutting back in, if there was silence for a second or so.... which obviously isn't ideal.

Also does anyone know how I can use the + wire for the audio output on the phone to give the stereo a - signal when its live ?

Sorry if this is simple but I'm no electronics guru, so if you can keep it as n00b as possible :lol:

Many thanks, merry christmas everyone.
Neil

 

[Gundy]

Could you use a “sound activated relay” circuit??
Like this one: **broken link removed**
Putting it on the cellphone output.

What do you have built so far???
What are you using for the input of the mic?

I am not much help on your problem. but I am hoping you may be able to help me

 

[Swifty]

Thanks,
Nothing built yet, still in the planning stages.
I am hoping to use a tie clip style mic, mounted in the car along with a small amplifier, that then runs to the relevant pins on the phone.