4-way (???) Switch for a Car

[JHZR2]

Hi,

I need a switch for my car that does a strange (to me) thing. Unlike a three-way switch, which would connect one thing to two different ones (depending upon which way the switch was set), I need a switch that does two mutually exclusive, different things, depending upon which way it is set.

Here is what I want to do:
I plan to install a wired FM modulator into my 91 BMW. You cannot get a matching, good looking headunit for that type of car, and I like the OE look. With a wired modulator, I can get as clear a signal as possible for my sirius radio and my ipod.

Here is the thing... I'd PREFER to set it up so that when I switch 12V to the FM modulator, it opens the circuit for the antenna (12V relay signal from the radio), and when I open the circuit for the FM modulator, it closes the circuit for the antenna 12V, so the antenna goes up (because Id be listening to regular radio).

The 12V from the radio for the antenna is not what I desire to use for the FM modulator, merely because I do not know that it can provide the amperage for the modulator (whatever that amount is). Otherwise I'd be using a 3-way off of the radio antenna 12V signal line. Id rather not chance messing up my radio, and thus would rather tap the 12V for the modulator elsewhere.

So I need a switch which in one position closes one circuit, and in the other position closes the other circuit. It should be set up so that at no time can both circuits be closed. There could be a 'neutral' position, where both ircuits are open though.

I say Id prefer it this way, because if need be, Ill just have the antenna out all the time, even when not listening to terrestrial radio. It would be OK, but If anyone knows of such a switch (and it needs to be compact too!), Id appreciate hearing about it.

Two switches just wont fit where I want to mount it...

Any thoughts???

Thanks!

JMH

 

[Spitty]

Sounds like you need a DPDT relay.

 

[JHZR2]

If its complex such that I need a relay, Ill likely live with the antenna being up all the time. Not the end of the world...

But I can envision a simple switch... its a matter if one exists...

Thanks!

JMH

 

[brianl703]

SPDT or DPDT switch, available at Radio Shack.

http://www.radioshack.com/product/index....rentPage=search

They have other styles available should you not like the looks of that one.

 

[XS650]

That sounds like a regular dpdt switch with open center.

Radio 12V power to the antenna on one pole in one position, 12V power from another source on the other pole to the modulator in the other position. I think most dpdt switches are make before break by default.

Am I missing something?

 

[XS650]

Originally Posted By: brianl703
SPDT or DPDT switch, available at Radio Shack.

http://www.radioshack.com/product/index....rentPage=search

They have other styles available should you not like the looks of that one.


Great minds think alike. After carefully parsing his sentences I came to the conclusion that he needs a dpdt because he want's to use separate power sources.

 

[JHZR2]

yes, exactly... two power sources to two different loads. Never should they be connected in any other way than to each other.

Thanks,

JMH

 

[JHZR2]

Just to be definite... all I want the switch to do is make connections between one source and one load in the one position:

And another source and load in another position:

Some of the reading Ive been doing about DPDT switches discuss 4 "out" terminals, which to me seems to have the potential to mess up, or have too complex a switching scheme (more than just two positions and maybe an 'off' where nothing is connected to anything). I can chart it all out with my ohmmeter, but I just want to be sure Im getting the right thing...

Just want to confirm...

Thanks,

JMH

 

[JHZR2]

understand now given the diagrams found here:
http://www.1728.com/project2.htm

The two extra terminals are for doing reverse polarity. Ill wire mine up as interupts in the +12V line and all will be fine.

Thanks all for the help!

JMH

 

[brianl703]

I'd just put ignition key switched 12V into the middle contact and the feed to the power antenna on the top contact and the feed to the FM modulator on the bottom contact (this uses three contacts all on one side).

This way doesn't use the 12V power antenna output from the radio.

Then:

up = power antenna up.
down= power antenna down, FM modulator on.
middle=power antenna down, FM modulator off.

But if you do NOT want the power antenna up with the radio off (since the above scheme allows that), then:

Connect the power antenna output from the radio to the left middle contact. Connect the power antenna feed to the left top contact.

Connect the 12V switched to the right middle contact. Connect the FM modulator to the right bottom contact.

Now the switch works like this:

Up = power antenna up but only when radio on
Middle = power antenna down, FM modulator off
Down = power antenna down, FM modulator on

Incidentally, have you looked at the Blaupunkt head units, like the Key West MP36? These look pretty nice compared to the flashy junk you usually find out there.