Line powered audio switch, is this feasible ?

[OBones]

Hi

I've got a mechanical audio switch that does this:

o- Spk L
Out L -o--__
o- TV L


o- Spk R
Out R -o--__
o- TV R


It's really a simple thing, and for my own knowledge, I was wondering if
it would be possible to replace this with an electronic switch. I can
always use analog switches (FSA4157A, ADG884 for instance) but these
require an external power source.
So I was just wondering if one could draw enough current from the line
to actually power the switches. If this is not feasible, that's no big
deal, I'd just like to hear about possibilities in this area.

Cheers
Olivier

 

[Luhan Monat]

OBones wrote:

Hi

I've got a mechanical audio switch that does this:

o- Spk L
Out L -o--__
o- TV L


o- Spk R
Out R -o--__
o- TV R


It's really a simple thing, and for my own knowledge, I was wondering if
it would be possible to replace this with an electronic switch. I can
always use analog switches (FSA4157A, ADG884 for instance) but these
require an external power source.
So I was just wondering if one could draw enough current from the line
to actually power the switches. If this is not feasible, that's no big
deal, I'd just like to hear about possibilities in this area.

Cheers
Olivier

Line powered? I doubt it. If someone can, I'll ad it to my 'bag-o-tricks'.

Minimully, you need external power to run a PIC12F675. Analog inputs
monitor all four source channels, determine which is currently active
and engage a DPDT relay to route the sound (assuming you are swithcing
speaker level).

Otherwise, CD4052 4:2 Analog Mux instead of a relay to switch line level
signals.


--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm

 

[martin griffith]

On Tue, 19 Apr 2005 13:16:15 -0700, in sci.electronics.design Luhan
Monat <x@y.z> wrote:

OBones wrote:
Hi

I've got a mechanical audio switch that does this:

o- Spk L
Out L -o--__
o- TV L


o- Spk R
Out R -o--__
o- TV R


It's really a simple thing, and for my own knowledge, I was wondering if
it would be possible to replace this with an electronic switch. I can
always use analog switches (FSA4157A, ADG884 for instance) but these
require an external power source.
So I was just wondering if one could draw enough current from the line
to actually power the switches. If this is not feasible, that's no big
deal, I'd just like to hear about possibilities in this area.

Cheers
Olivier

Line powered? I doubt it. If someone can, I'll ad it to my 'bag-o-tricks'.

Minimully, you need external power to run a PIC12F675. Analog inputs
monitor all four source channels, determine which is currently active
and engage a DPDT relay to route the sound (assuming you are swithcing
speaker level).

Otherwise, CD4052 4:2 Analog Mux instead of a relay to switch line level
signals.
try center tapped tranformers and phantom power to a relay at the

distant end.
QED



martin

After the first death, there is no other.
(Dylan Thomas)

 

[Pooh Bear]

OBones wrote:

Hi

I've got a mechanical audio switch that does this:

o- Spk L
Out L -o--__
o- TV L

o- Spk R
Out R -o--__
o- TV R

It's really a simple thing, and for my own knowledge, I was wondering if
it would be possible to replace this with an electronic switch. I can
always use analog switches (FSA4157A, ADG884 for instance) but these
require an external power source.
So I was just wondering if one could draw enough current from the line
to actually power the switches. If this is not feasible, that's no big
deal, I'd just like to hear about possibilities in this area.

By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?


Graham

 

[OBones]

Pooh Bear wrote:

By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?

It comes out of my PC, so I guess it is Line level.
Basically, for the "fun" of it, I just want to select between two
destinations for the signal, depending on a touch button.
Press, goes to A, Press again, goes to B.

 

[Pooh Bear]

OBones wrote:

Pooh Bear wrote:

By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?

It comes out of my PC, so I guess it is Line level.
Basically, for the "fun" of it, I just want to select between two
destinations for the signal, depending on a touch button.
Press, goes to A, Press again, goes to B.

Ok - if it's 'line level' there's no power in the signal to talk of. It might
just be possible to do something with a speaker level connection.

Other than that it's down to 'phantom power' being used. Are you familiar with
this ? The centre tapped transformers suggested by Martin could be replaced by
active circuitry btw. Then again you could replace the switch with a relay and
simply run a DC control / power signal to it.

Another option is to find a sound card with 2 sets of line outs, wire them
independently to their destinations and select the one you want from the sound
card's control panel.

Graham

 

[martin griffith]

On Tue, 19 Apr 2005 22:02:29 +0100, in sci.electronics.design Pooh
Bear <rabbitsfriendsandrelations@hotmail.com> wrote:

Another option is to find a sound card with 2 sets of line outs, wire them
independently to their destinations and select the one you want from the sound
card's control panel.

Graham

bet you cant do that with "one touch of a button "

martin

After the first death, there is no other.
(Dylan Thomas)

 

[Pooh Bear]

martin griffith wrote:

On Tue, 19 Apr 2005 22:02:29 +0100, in sci.electronics.design Pooh
Bear <rabbitsfriendsandrelations@hotmail.com> wrote:

Another option is to find a sound card with 2 sets of line outs, wire them
independently to their destinations and select the one you want from the sound
card's control panel.

Graham

bet you cant do that with "one touch of a button "

martin

Who said GUIs make sense ?


Graham

 

[OBones]

Pooh Bear wrote:

OBones wrote:


Pooh Bear wrote:


By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?

It comes out of my PC, so I guess it is Line level.
Basically, for the "fun" of it, I just want to select between two
destinations for the signal, depending on a touch button.
Press, goes to A, Press again, goes to B.


Ok - if it's 'line level' there's no power in the signal to talk of. It might
just be possible to do something with a speaker level connection.

Well, the output works well with headphones, but I agree these do not
require much power anyway.

Other than that it's down to 'phantom power' being used. Are you familiar with
this ? The centre tapped transformers suggested by Martin could be replaced by
active circuitry btw. Then again you could replace the switch with a relay and
simply run a DC control / power signal to it.

No, I'm not familiar with phantom power, and I would greatly appreciate
any pointers. I will do a search on google, but pointers from those with
experience is always better.

Another option is to find a sound card with 2 sets of line outs, wire them
independently to their destinations and select the one you want from the sound
card's control panel.

That is not an option, it's the laptop sound card I'm talking about, and
I can't replace it.

Thanks
Olivier

 

[martin griffith]

On Wed, 20 Apr 2005 09:19:45 +0200, in sci.electronics.design OBones
<obones_gfd_@_gfd_altern.org> wrote:

Pooh Bear wrote:

OBones wrote:


No, I'm not familiar with phantom power, and I would greatly appreciate
any pointers. I will do a search on google, but pointers from those with
experience is always better.


Another option is to find a sound card with 2 sets of line outs, wire them
independently to their destinations and select the one you want from the sound
card's control panel.

That is not an option, it's the laptop sound card I'm talking about, and
I can't replace it.

Thanks
Olivier
crood circuit on

http://uk.geocities.com/martingriffith/phant.PDF




martin

After the first death, there is no other.
(Dylan Thomas)

 

[OBones]

Thanks,

That requires a battery, which is not really good.

How do headphones work? Where do they get the power from?
Or are they small enough that the very little current on the line is enough?

 

[martin griffith]

On Wed, 20 Apr 2005 10:49:58 +0200, in sci.electronics.design OBones
<obones_gfd_@_gfd_altern.org> wrote:

Thanks,

That requires a battery, which is not really good.

How do headphones work? Where do they get the power from?
Or are they small enough that the very little current on the line is enough?
just reposted it with a battery free remote end. just watch out for

putting too much current through the transformer




martin

After the first death, there is no other.
(Dylan Thomas)

 

[OBones]

martin griffith wrote:

On Wed, 20 Apr 2005 10:49:58 +0200, in sci.electronics.design OBones
obones_gfd_@_gfd_altern.org> wrote:


Thanks,

That requires a battery, which is not really good.

How do headphones work? Where do they get the power from?
Or are they small enough that the very little current on the line is enough?

just reposted it with a battery free remote end. just watch out for
putting too much current through the transformer

Is it me or there are two batteries in that new diagram?
Sorry to bother you with that.

 

[martin griffith]

On Wed, 20 Apr 2005 11:20:34 +0200, in sci.electronics.design OBones
<obones_gfd_@_gfd_altern.org> wrote:

martin griffith wrote:

On Wed, 20 Apr 2005 10:49:58 +0200, in sci.electronics.design OBones
obones_gfd_@_gfd_altern.org> wrote:


Thanks,

That requires a battery, which is not really good.

How do headphones work? Where do they get the power from?
Or are they small enough that the very little current on the line is enough?

just reposted it with a battery free remote end. just watch out for
putting too much current through the transformer

Is it me or there are two batteries in that new diagram?
Sorry to bother you with that.
nope ,it's you!

the top cct, just has a power source at the sending end, and the
center tap on the distant end drives the relay coil directly.

The lower circuit has a second power source, so that you dont send a
lot of DC through the tranny, just enough to turn on the transistor,
which controls the relay. This is the prefered method, by us, who know
these things!

the screen of the cable it how the circuit is completed.

This may not be suitable for you if you are running single screened
cables. Normally most pro audio stuff is run balanced, But doing what
you want without external power is basically "difficult".


martin

After the first death, there is no other.
(Dylan Thomas)

 

[OBones]

martin griffith wrote:

The lower circuit has a second power source, so that you dont send a
lot of DC through the tranny, just enough to turn on the transistor,
which controls the relay. This is the prefered method, by us, who know
these things!

Oh okay. Didn't see it like that.

the screen of the cable it how the circuit is completed.

That, I understood already.

This may not be suitable for you if you are running single screened
cables. Normally most pro audio stuff is run balanced, But doing what
you want without external power is basically "difficult".

Ok, I'll forget it then and keep my mechanical inverter. Thanks for the
help.

 

[Rich Grise]

On Tue, 19 Apr 2005 22:50:08 +0200, OBones wrote:

Pooh Bear wrote:

By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?

It comes out of my PC, so I guess it is Line level.
Basically, for the "fun" of it, I just want to select between two
destinations for the signal, depending on a touch button.
Press, goes to A, Press again, goes to B.

Why not just a DPDT, push-on, push-off switch? I guess it'd be more
accurate, with a DPDT, to call it "push-A, push-B".

Good Luck!
Rich

 

[OBones]

Rich Grise wrote:

On Tue, 19 Apr 2005 22:50:08 +0200, OBones wrote:


Pooh Bear wrote:


By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?

It comes out of my PC, so I guess it is Line level.
Basically, for the "fun" of it, I just want to select between two
destinations for the signal, depending on a touch button.
Press, goes to A, Press again, goes to B.


Why not just a DPDT, push-on, push-off switch? I guess it'd be more
accurate, with a DPDT, to call it "push-A, push-B".

Yeah, that's definitely possible, but it has some mechanical parts, and
I'm in my "all electronics" period.
So i'm just wondering if it's possible to draw enough power from a
regular line out of a PC to drive very few components that would act
just like a DPDT switch.
But it seems I'm dreaming awake, so i'll let that great idea go away...

 

[Walter Harley]

"OBones" <obones_gfd_@_gds_altern.org> wrote in message
news:4265545c$0$7209$626a14ce@news.free.fr...

> So I was just wondering if one could draw enough current from the
line to actually power the switches.

Others have already discussed options and feasibility. To fill in the
background:

"Line level" from a non-pro-audio sound card (that is, the kind whose output
is on a stereo minijack that you can plug headphones into) is typically a
nominal voltage (at full output) of a bit less than 1V, with a source
impedance of perhaps 100 ohms. So, with maximum signal, the power you can
get is 1V at 10mA, that is, 10mW.

But that's assuming you're sending a lot of signal out the output. You also
need to consider what happens in between songs, when there is no signal at
all. At that point you're getting zero power.

And, you need to take into account that if you do derive power from the
audio signal, you're going to be presenting the sound card with an
additional load. It is challenging to turn AC (your audio signal) into DC
(what you probably need to power your switch circuitry) without creating a
load that is different at different voltages; that's what people are talking
about when they talk about "power factor correction" in power supplies. The
consequence of an uneven load in this case is significant audio distortion.

So, plan on being able to derive around a microwatt of useful, reliable,
continuous power from your consumer line-level audio output. And even
getting that will be a little tricky.

But why bother? If your circuitry can run on a microwatt - which is not
impossible these days - then it can run on a lithium battery for 10 years.
Is that really so unacceptable? It's probably longer than the life of the
computer.

Still, sometimes mechanical is the right way to go. This is one of those
times.

 

[Rich Grise]

On Wed, 20 Apr 2005 17:45:40 +0200, OBones wrote:

Rich Grise wrote:
On Tue, 19 Apr 2005 22:50:08 +0200, OBones wrote:
Pooh Bear wrote:

By 'line powered' do you mean powered by the audio signal ? Is it speaker
level ?

It comes out of my PC, so I guess it is Line level.
Basically, for the "fun" of it, I just want to select between two
destinations for the signal, depending on a touch button.
Press, goes to A, Press again, goes to B.

Why not just a DPDT, push-on, push-off switch? I guess it'd be more
accurate, with a DPDT, to call it "push-A, push-B".

Yeah, that's definitely possible, but it has some mechanical parts, and
I'm in my "all electronics" period.
So i'm just wondering if it's possible to draw enough power from a
regular line out of a PC to drive very few components that would act
just like a DPDT switch.
But it seems I'm dreaming awake, so i'll let that great idea go away...

You want your "Line out" to go to either the "Line in" of equipment A
or the "Line in" of equipment B, right?

Why not just "Y" it and sent it to both? You're not going to be using
them both at the same time, are you? Just let the one you're not
using ignore the input. If you're ookie about isolation, and don't
trust your grounds, then put a 1K ~ 10K resistor in series with each
arm of the "Y".

+----/\/\/\/----- to A
|
From Source ------------+
|
+----/\/\/\/----- to B

Cheers!
Rich

 

[Dave Moore]

If you want to switch it remotely via a single two conductor
wire, you could use the phantom power of the sound cards
microphone input or power from the sound cards MIDI\game
port to power an analog switch.

Alternatively you could derive power from a serial or parallel port
connector or a USB port.



"OBones" <obones_gfd_@_gfd_altern.org> wrote in message news:d457s4$5ti$1@reader1.imaginet.fr...
: martin griffith wrote:
:
: > The lower circuit has a second power source, so that you dont send a
: > lot of DC through the tranny, just enough to turn on the transistor,
: > which controls the relay. This is the prefered method, by us, who know
: > these things!
:
: Oh okay. Didn't see it like that.
:
:
: > the screen of the cable it how the circuit is completed.
:
: That, I understood already.
:
:
: > This may not be suitable for you if you are running single screened
: > cables. Normally most pro audio stuff is run balanced, But doing what
: > you want without external power is basically "difficult".
:
: Ok, I'll forget it then and keep my mechanical inverter. Thanks for the
: help.