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Head unit phone signal

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=23529
Printed Date: July 22, 2025 at 11:38 AM


Topic: Head unit phone signal

Posted By: Rortec
Subject: Head unit phone signal
Date Posted: December 29, 2003 at 7:37 AM

Hi Guys,

As you all know many head units have a phone mute wire.

What i would like to know is what signal (+/-) is used for the mute feed?

Cheers

Rory




Replies:

Posted By: Teken
Date Posted: December 29, 2003 at 10:22 AM
Rortec wrote:

Hi Guys,


[PWhat i would like to know is what signal (+/-) is used for the mute feed?



Normally this is a (-) negative pulse, coming off from the phone.

Regards

EVIL Teken . . .




Posted By: Rortec
Date Posted: December 29, 2003 at 12:55 PM

Cheers Teken,

What voltage is this normally?

What i am trying to say is can this be triggered direct from the phone handset or does it need to be manpulated before going to the phone mute?

Regards

Rory





Posted By: Teken
Date Posted: December 29, 2003 at 10:40 PM
Rortec wrote:

What voltage is this normally?


If this is a *in care phone, then it is based on a +12 volt power supply. If this phone is one which you carry in your pocket, that is dependant upon each of the phone manufacture(s).

Some people have those *hands free* speaker boxs which interface with the hand held phone. At that point the phone is being powered by a +12 volt source, with a step down power supply, normally 3.80 volts aprox.

Which then gets plugged into the portable phone.


The mute feature is *normally* part of the hands free also, and many people interface that part of the *hands free* device to the vehicles horn.

This is the same principle as the radio, that you wish to interface.

Below I will list the connections for the horn honk alert, and you can apply this to your head unit, if you wish. I will provide both arrangements for positive and negative source horns that you may encounter.


85 = Output wire from phone / hands free device. (-)

86 = +12 volts fused @ 5 amps

87 = +12 volt type horn, which is grounded

30 = +12 volts tied to pin 86



======================================================


85 = Phone output

86 = +12 volts fused @ 5 amps

87 = Ground type horn, whitch is tied to +12 volts

30 = Ground (-)


If you need to reverse the polarity for any of the units in question you will find the schematic on this site as well.

If you would like me to post it, I will do so as well.

I hope this gives you some insight into your project.


Regards

EVIL Teken . . .





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