I have replaced my Becker Headunit with a new Nakamichi one (very happy with that improvement).
My Nokia carkit could mute the factory radio through its mute function (which was good so that my phone does not answer when the radio is too loud).
The Nakamichi headunit does not have a mute wire to interrupt it automatically. So I want to interrupt the accessory power (with a relay) to it so that the radio will simply shut off (same as when you turn off engine) when the call comes through and come back on when the phone is hung up.

Please advise on the installation of the relay. I don't know if the mute wire was a ground wire or a hot wire. I am sure someone here knows the answer.

check my page, click menu #13 and look at pin A-3: "phone mute: ground to activate".

Start from there and check it out by measuring the pin's voltage and ground it thru a small value resistor (10 ohms). Measure voltage drop and calculate current thru resistor.

If ok, then ground it without resistor. Radio should mute.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

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Thanks. But I am not looking to mute the OE headunit, I knew how to do that. I want to setup a relay to disconnect power to the new headunit when the phone answers. Is that clearer?

I answered your question. Since the Nokia interfaced ok with the Becker (ie muted the radio when the phone was active), it had to be ground when active. That's because the Becker needed a "ground" to mute. Is that clearer?

For the Nak, your relay idea using the Nokia's mute line to provide ground to energize the relay, thereby removing power from the Nak. Do this by wiring the Nak's power through the normally closed contacts of the relay. Understand?

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

I now understand, thanks. My engineering is a little rusty since I chose a totally different career.

Normally close for the Nak accessory power makes sense.
I hate to confess my ignorance but I have not installed a relay before - although I obviously do not think there can be much to it.

The activating, coil section, of the relay I assume should be fed by a hot wire and the mute ground. This way the loop closes when Nokia grounds the wire and the Normally closed circuit opens.

There's one thing to consider; will the Nokia's 'mute' line be able to sink the current from the relay coil.

Before you do this, test out to make sure that it will work. Take a 470 ohm resistor with one end hooked to +12V. Connect the other end to the Nokia mute line. Use a voltmeter and monitor the voltage at the resistor/Nokia mute line junction. It should read about 12V. Make a call and see what the voltage is. If 'perfect', it will drop to 0V, but probably will be some voltage there.

Even if it's 1 or 2 volts, the relay will still energize. The lower the relay coil current, the better the mute line will 'sink' the current.

Suggest that you use a low power 5 Amp relay such as Radio Shack 275-249. See the 2001 catalog, page 268. Sorry, don't know what the coil current is but it should be low. This relay will handle 5 amps. So you need to know how much current the Nak draws when you have it 'cranking'. This will determine how much current the relay's contacts must handle without 'welding'.

Also you may be able to use a Solid State Relay (SSR), Radio Shack 275-310 on page 268. This SSR will handle 3 amps. Here's how to use it:

Pin 1: +12V
Pin 2: to Nak power pin(s)
Pin 3: connect to 12V through a resistor, probably 470 ohms or smaller. Use the largest resistor that will still operate the SSR for the given NAK current draw.
Pin 4: to Nokia mute line.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Well, thanks a lot. This is tremendously helpful!