Shoutbox

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Originally posted by Mike

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Originally posted by lizard.boy
If you can find a decent 6PDT switch, it's very possible it would work.

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Define "decent" please

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Priced right, doesn't feel like it'll fall apart in your hands. (not uncommon for cheap stuff)

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Originally posted by lizard.boy
Though I'm pretty sure you don't need to switch the subwoofer, so you would only need a 5PDT.

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Do these even exist? A Google Image search for 5PDT shows irrelevant images, but does show some pictures of 6PDT switches when searching for 6PDT.

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Forgot about that, very possible it dosn't exist.

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Originally posted by lizard.boy
The following information may make it clearer, it may make it worse. if you don't fully understand I don't blame you, just disregard it. There's no real solution here, just some background on relays.

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Thanks, now relays make more sense

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Your Welcome

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Originally posted by lizard.boy
I would highly suggest NOT combining your center and left/right speaker channels. It's typically not expected when the receiver company builds the receiver and you don't know what will happen when the power is coming/going from different channels.

My solution would be to add an additional center channel speaker and switch between the two instead of trying to mix the audio signals. If you're only using 2 channel audio you may not even notice that you don't have it..

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Alright, thanks, I'll keep that in mind. I'll see if I can add speaker on the desk.

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If your switching before the amplifier or receiver, that is not possible, so also keep that in mind.

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Originally posted by lizard.boy
EDIT: To answer your question in the other forum, yes you would need a power source to operate your relays. An old 5V wall charger from a cell phone would probably be your best bet.

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Bah!
Having a power source seems weird since I will only be rerouting the signals
Is there any reason to prefer relays over a standard switch?

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Not in this case, Relays are preferred where you want to control the circuit electrically when another device turns on for example. In this case it would be easier to have one switch turn on 3 DPDT relays instead of hitting 3 switches each time you change your seat. (for example) You could also remotely locate the swicth by running 2 wires instead of 12 (6 in 6 out).

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Originally posted by stoshrocket
might be worth noting it could well be a cheaper and less confusing (debatable) to use multiple smaller relays, ie 2 x 3PDT or even 3 x DPDT.

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Can you create an example diagram please? I can imagine how the diagram for using a 5PDT/6PDT would be, but I'm not sure about this one

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Not quoting me, but that's ok. For example, you can use 3 relays with the same switch operating 3 coils and they will operate in unison. This is probably the route you will want to take if you are using relays, since they are much easier to find than 6 pole relays. It would work exactly like a 5P/6P except it would be more physical units with the coil (control) side wired in parallel.

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Originally posted by lizard.boy
My first instinct would be to place the device between the receiver and the speakers, instead of the PC and the receiver, and switch the "grounds" at the same time as switching the channels.

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Hmmm ... that would be hard because I use two different receivers (one for the L/R channels and another one for the rest of the channels).

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Depending on how your speakers are hooked up, it may not matter if they are connected to 1, 2, or 6 receivers/amplifiers. Does the end of the speaker cables have 2 bare wires in pinch jacks, rca jacks, or some sort of proprietary connection?

I thought I already posted this, but guess I just wrote it and never hit "post".

You can re-wire a VGA or parallel switchbox, a mechanical one like this.  It will provide a suitable switch as well as a housing.

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Originally posted by lizard.boy
I don't know if mixing return paths between the 3 outputs on the motherboard is acceptable or not, so it's quite possible that you would need to factor that into your design.

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I expect that it would be.  I am sure they are all just a common ground.

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Originally posted by lizard.boy
My first instinct would be to place the device between the receiver and the speakers, instead of the PC and the receiver, and switch the "grounds" at the same time as switching the channels

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I think switching inputs is a better idea, because here you are not only going to deal with considerable current, but you will also have to switch twice as many lines (speaker returns usually are not common grounds).  Also, anything shorting out here, even momentarily, could blow the amplifier.

NB: Example of multiple relays wiring:



(Sorry about the slightly wierd overlapping wiring on the relay side, it's basically three relays in parallel but showing them side by side too too much room...)

This will act in the same way as a single 6PDT in place of the 3 DPDT, but in my experience this way would be cheaper and less confusing only switching the 2 channels per relay. If it turns out you end up not switching central and SW then you can obviously remove the bottom relay (or just use a single 4PDT).

As for 5PDT, I'm pretty sure they'd exist, it's not like you need an even number of inputs, 3PDT are quite common. However, I'd still stick down the multiple DPDT route, it'll just make things easier, I've personally never seen anything larger in a simple pin format, from the amounts of times I've wired something wrong with a larger relay I've just ended up thinking it's not worth the hassle!

So let me get this straight... If I take the relay route (which looks like is what I'll be taking), I'll have to build the following circuit, right (sorry for the crappy diagram)?



Also, I should be able to use power from a USB port, right?

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Originally posted by Adeptus
You can re-wire a VGA or parallel switchbox, a mechanical one like this.  It will provide a suitable switch as well as a housing.

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Thanks. Hmmm ... that looks a little harder


EDIT: Thanks stoshrocket, that diagram looks a lot better than mine

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Originally posted by Mike
Also, I should be able to use power from a USB port, right?

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You can easily draw 500mA at 5V from a Usb port. If you wanted to get really fancy you could throw some transistors and a flip flop and have it USB controlled, but I'd stick to just getting it working. All kidding aside, Getting power should be no problem though, just make sure your relays aren't too power hungry. Interfacing with USB is much harder and probably way overkill for your application.

I'm pretty sure that diagram is correct if your inputs are on the bottom. Not sure if it'd work in both directions. I'm assuming that when you're in your PC position the plan is to simply turn off the centre channel. Also: save yourself some connections and don't bother running the sub through the relay.

So, to sum up, I will need:

-A construction box to house my project
-6 female 3.5mm audio ports
-3 line-in cables
-3 DPTD relays
-Some way to draw power from USB (I cut an extension cord for this purpose)
-A switch
-Lots of wires

By the way, should I go with a solid state relay? Is there anything more I need to ask for the relay at the store (example: voltage), or asking for "3 DPTD relays" is enough?

Thanks

EDIT: I was reading this:

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Originally posted by http://www.geofex.com/Article_Folders/relays/relays_for_switching_audio_signa.htm
There are some other things you need to know. Those coils in the electromagnets  - they act like (and are!) inductors. When you set up current in them to make the relay switch positions, you are loading up an inductor with current. When you try to turn it off, the inductor responds by reversing its voltage to try to keep the current flowing. This happens as fast as you can cut the current off, so inductors can make very fast, sharp voltage spikes. Since inductance varies as the square of the number of turns on a coil, it usually happens that many turns of very thin wire on a higher-voltage (and hence, lower current) version of a relay will have much larger inductance than the same-physical-size relay in a lower voltage (hence, fewer turns of larger copper wire) version. The coil inductance directly slows down the build up and ramp down of current in the coil when you apply a voltage, so in general, higher voltage relays take longer to operate.

The fast, sharp voltage spike that comes from the relay coil reversing its voltage to try to keep the current flowing can kill your driver transistor. You have to protect the device from the voltage spike. This is usually done by placing a diode in parallel with the relay coil, but in a direction where the diode does not conduct when the relay coil is turned on. The diode only conducts when the relay coil reverses the voltage across it at turn-off. This clamps the voltage spike to only one diode drop more than the power supply voltage.

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Should I worry?

In this case you're not driving the relay with a transistor, so the reverse diode isn't quite as important. It is important to make sure you're using a relay with the correct coil voltage.

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Originally posted by lizard.boy
It is important to make sure you're using a relay with the correct coil voltage.

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Is that the lowest voltage that can make the relay switch (which in my case needs to be <=5V)?