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Old 10-05-2001, 10:56 AM
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JimF JimF is offline
'94 S500: only 793 sold!
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,924
that's the way to do it!

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

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Last edited by JimF; 10-05-2001 at 07:39 PM.
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