Audio switch project.

[vr4Legacy]

I am working on building an audio switch for my car that will allow me to hook my XM input and my iPhone (both 3.5mm) and switch between them on a single 3.5 mm output. I have seen plans and understand how to make one with a 3PDT switch.

I have found several inexpensive 3PDT toggle switches, however I would prefer to use a rocker switch so it looks cleaner. I can't find one for less than $15-$20, and since the point of this project is to avoid paying $30 for a prebuilt switch, I don't want to go that route.

If I understand how a 3.5mm plug works, there is a left and right channel and a ground.

The diagram I saw switched all three between the two, hence needing a 3 pole switch.

My question is, could I share the ground between the 3 at all times, and simply use a DBDT switch to swith the L&R Channels? Would this create a ground loop?

Also, is there an inexpensive 3PDT Rocker switch that I just can't find??

Lastly, how hard/expensive would it be to make the switch load sensing, hence automatic?

Thanks for any help!

 

[shrtrnd]

You may have to check a few, but auto parts stores should carry what you need.
(Or a place that caters to truckers)
People are big into doing what you're doing, and the demand at auto/truck places is high.
(RV repair/modification vendors also)
I got my last batch (years ago) of rocker switches from Radio Shack.
Your only problem should be finding the finish on the switch you want to match your vehicle.
$5 should be reasonable for a rocker switch. (but you can buy a Rambler or a Mercedes Benz type).

 

[vr4Legacy]

thanks for the reply shrtrnd, as for finish, I could really care less, it's going in my console, msot I see are black (which is fine) I'll paint if it need be, I just don't want a toggle that could get caught on something.

I'll keep looking. Do you happen to know if using a DPDT switch and sharing a ground will work? I'm really having trouble finding 3PDT Rocker switches.

 

[shrtrnd]

Sorry, I'm not up on these new-fangled communications power requirements.
Typically, the vehicle chassis is the car battery ground.
For the new high-tech comm gear, there may be special power filtering (you know, to
keep alternator noise and etc... off the power line.)
If your question is about the switch itself: DPDT IS two separate circuits. I'm not sure
about your reference to 'sharing a ground'. (Why you think you need a 3-Pole switch)
I'm hoping somebody who knows about XM Radio and iPhones is going to jump in
here and give you more exact information.
I keep thinking that your problem CAN'T be unique. That other people have the same
issue. And that being the case, there's a market for the switch you need.
If car, truck, RV elec parts suppliers don't have what you need. There are a lot of
on-line elec parts suppliers out there:
Parts Express, Crutchfield, Jameco, MCM, All Electronics Corp, ....
(Whoops, if you're not located in the States).
Sorry I don't have your exact information, but hopefully you've got a little more information
now, and somebody else might post a more useful reply.

 

[davelectronic]

Switch

Why not use a SPST or DPDT and use a relay lots of contact arrangements on them, some relays for that could be small.
Dave.

 

[vr4Legacy]

Thank you, you've been very helpful. As for the 'sharing a ground' I don't have a better term. But essentially, if I understand correctly, a 3.5mm plug has 3 leads, a L,R and Ground. I wasn't sure if any interference would transfer across if I simply joined them together from each input across to the output.

I understand the chassis is the ground, but with electronics and low level outputs, a ground loop is easy to create.

Thanks again for your help.

 

[vr4Legacy]

Why not use a SPST or DPDT and use a relay lots of contact arrangements on them, some relays for that could be small.
Dave.

Never thought of it to be honest. Good idea!

I'll see what I can find out.

 

[vr4Legacy]

Here's a quick schematic.

My only fear is that this will cause some interference running the audio through an energized relay. Any thoughts?

I found some info online that says it's ok to use a common ground. This schematic is to wire an led for each side.