Line powered audio switch, is this feasible ?

[OBones]

Rich Grise wrote:

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

Yeah, I tried that in the past, but the resulting quality was not
satifying as the TV input (say, A) was parsiting the speakers input (B).
Hence the will to separate the two. But that is indeed the simplest
circuit ;-)

 

[OBones]

Walter Harley wrote:

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.

Yeah, not worth the effort.

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.

Running on a microwatt is out of my field of expertise. If I go down to
10mA, I'm really happy ;-)

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

Yep, I figured that one out. Ah well, sometimes electronics is NOT the
answer ;-)

 

[Rich Grise]

On Thu, 21 Apr 2005 09:18:01 +0200, OBones wrote:

Rich Grise wrote:

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


Yeah, I tried that in the past, but the resulting quality was not
satifying as the TV input (say, A) was parsiting the speakers input (B).
Hence the will to separate the two. But that is indeed the simplest
circuit ;-)

Well, now even I'm confused.

Where is the signal coming from, and where is it going to? You sound
like you have inputs acting like outputs - PLEASE draw a picture
telling what's coming out of which box, which direction it's going,
and what you expect to see, where. ?:-/

Thanks,
Rich

 

[OBones]

I have the pc output
I have the TV input
I have the speaker input

However, those two inputs are definitely not clean, and the tv puts some
sort of feedback noise signal into the line. This happens even if the TV
is off (but still plugged) and "goes back" into the speakers if there is
no physical separation of the signals.

 

[Walter Harley]

"OBones" <obones_gfd_@_gfd_altern.org> wrote in message
news:d47io9$ivs$2@reader1.imaginet.fr...

Running on a microwatt is out of my field of expertise. If I go down to
10mA, I'm really happy ;-)

Read the chapter on low-power design in Art of Electronics, if you're
interested in learning more on the topic.

 

[OBones]

Walter Harley wrote:

"OBones" <obones_gfd_@_gfd_altern.org> wrote in message
news:d47io9$ivs$2@reader1.imaginet.fr...

Running on a microwatt is out of my field of expertise. If I go down to
10mA, I'm really happy ;-)


Read the chapter on low-power design in Art of Electronics, if you're
interested in learning more on the topic.

Thanks for the tip, I'll have a look at it.

 

[Joop]

"Walter Harley" <walterh@cafewalterNOSPAM.com> wrote:

"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.

Let's see if a latching relay might be fired by saving energy.

I looked up one that needs 5V at 139ohm for 6mS according to specs.
That is 0.18W during 6mS => 1mWS of energy

Then we route audio power (via an uptransformer) to a capacitor for
storage. Assuming we might be able to tap 1mW aside without putting
too much of a load on the line output, then 1 second of charging would
be required.
With some lower level signals and less then optimal transformer for
the full audio range, quit a bit more of time would be needed, but it
does seem feasable. How often do you need to switch signals?

Joop

 

[OBones]

Joop wrote:

Let's see if a latching relay might be fired by saving energy.
I looked up one that needs 5V at 139ohm for 6mS according to specs.
That is 0.18W during 6mS => 1mWS of energy

Then we route audio power (via an uptransformer) to a capacitor for
storage. Assuming we might be able to tap 1mW aside without putting
too much of a load on the line output, then 1 second of charging would
be required.
With some lower level signals and less then optimal transformer for
the full audio range, quit a bit more of time would be needed, but it
does seem feasable. How often do you need to switch signals?

Once every week, or something like that.
Yeah, I know, why bother with electronics for such a low usage? Well, as
I said, I'm just toying with ideas, that's my geeky side ;-)

Thanks for the input on the latching relay, that's a very interesting
idea. As to the uptransformer with a capacitor, I like that, but I'm not
sure how you'd do that. Is there a schematic I could have a look at ?

 

[OBones]

Okay, after giving a few thoughts to it, here is what I came up with:


1:6
Ina ---+---. ,---. .-----. ___ --- .-----.
| )|( '--|~ +|--|_R_|---+----o o--|Logic|-------.
| )|( .--|~ -|-. |+ '-----' |
Inb -+-)---' '---' '-----' | --- .-------.
| | | --- .--------| Latch |
| | | | | | Relay |
| | '--------+-------' | |
| | | |-- O1a
| '----------------------------------------------| |-- O1b
| | |-- O2a
'------------------------------------------------| |-- O2b
'-------'

(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

Calculating R is not a problem, but I have a hard time figuring out what
to put in the "Logic" box. I press the button, it puts the relay in Set
position, I press again, the relay goes back to Reset.

Thanks for any input.

 

[John Woodgate]

I read in sci.electronics.design that OBones
<obones_gfd_@_gfd_altern.org> wrote (in
<d4id8j$kn6$1@reader1.imaginet.fr&gt about 'Line powered audio switch, is
this feasible ?', on Mon, 25 Apr 2005:

Calculating R is not a problem, but I have a hard time figuring out
what to put in the "Logic" box. I press the button, it puts the relay
in Set position, I press again, the relay goes back to Reset.

Change the bridge rectifier to an op-amp full-wave rectifier to improve
efficiency. You want to draw as little power as possible from the audio.
For 'logic' you need a D-type bistable.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[OBones]

John Woodgate wrote:

I read in sci.electronics.design that OBones
obones_gfd_@_gfd_altern.org> wrote (in
d4id8j$kn6$1@reader1.imaginet.fr&gt about 'Line powered audio switch, is
this feasible ?', on Mon, 25 Apr 2005:

Calculating R is not a problem, but I have a hard time figuring out
what to put in the "Logic" box. I press the button, it puts the relay
in Set position, I press again, the relay goes back to Reset.


Change the bridge rectifier to an op-amp full-wave rectifier to improve
efficiency. You want to draw as little power as possible from the audio.
For 'logic' you need a D-type bistable.

Thanks for the tip on the op-amp, I'll have a look. But does this mean I
need to add a diode just before the resistor so that the capacitor does
not unload itself into the op-amp ?

I also initially thought of D-type bistable, but this will draw current
permanently from the capacitor. Plus the relay does not need permanent
injection, just a pulse.
Basically, and maybe I'm wrong, what was intended by Joop was to load a
capacitor as slowly as possible from the audio line and then use that
stored charge to trigger the latching relay when the push button is pressed.

 

[John Woodgate]

I read in sci.electronics.design that OBones
<obones_gfd_@_gfd_altern.org> wrote (in
<d4ikfe$mbs$1@reader1.imaginet.fr&gt about 'Line powered audio switch, is
this feasible ?', on Mon, 25 Apr 2005:

Thanks for the tip on the op-amp, I'll have a look. But does this mean
I need to add a diode just before the resistor so that the capacitor
does not unload itself into the op-amp ?

No. The diodes in the op-amp rectifier circuit do that.

I also initially thought of D-type bistable, but this will draw current
permanently from the capacitor.

Very little.

Plus the relay does not need permanent injection, just a pulse.

OK, you could use a monostable, but since you have a push-button, why
bother?

Basically, and maybe I'm wrong, what was intended by Joop was to load a
capacitor as slowly as possible from the audio line and then use that
stored charge to trigger the latching relay when the push button is
pressed.

Yes.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[OBones]

Well, now I'm confused.
Let me explain what I understood and ask a few questions along the way.

1. The step up transformer is used to get about 6Volts from the 1V audio
signal. That's fine. Out of curiosity, could this be replaced by a diode
voltage multiplier?

2. The diode bridge is used to make this into a positive voltage. This
could be replaced by op amps as you suggested. But where do these get
the VCC-VSS from? Directly from their own regulation of the output of
the transformer?

3. The positive voltage is fed into the capacitor through a resistor so
that the current drawn from the transformer is very small. Charge time
is thus longer (one second or more), but it's not a problem for that
applicaton.

4. The push button is depressed, the "logic" box connects the capacitor
to the first coil for a short time. During this time, the capacitor
discharges itself almost completely into the coil. This, to me, is
required because of the relatively high energy required to have the coil
operate.

5. The capacitor loads itself again.

6. The button is depressed a second time, the logic connects the
capacitor to the second coil of the relay, thus changing its position.


What I have a hard time understanding is how a D-Type flip flop would
remember its previous state when the charge in the capacitor is gone,
thus reducing the voltage to almost nil.
Note that I'm indicating a two coil latching as it seems easier to
connect one coil or the other rather than invert the polarity of the
voltage applied to the singe coil.

Thanks a lot for your advices, they are very well appreciated.

Olivier

 

[John Woodgate]

I read in sci.electronics.design that OBones
<obones_gfd_@_gfd_altern.org> wrote (in
<d4iqk6$nka$1@reader1.imaginet.fr&gt about 'Line powered audio switch, is
this feasible ?', on Mon, 25 Apr 2005:

Well, now I'm confused.
Let me explain what I understood and ask a few questions along the way.

1. The step up transformer is used to get about 6Volts from the 1V
audio signal. That's fine. Out of curiosity, could this be replaced by
a diode voltage multiplier?

No.

2. The diode bridge is used to make this into a positive voltage. This
could be replaced by op amps as you suggested. But where do these get
the VCC-VSS from? Directly from their own regulation of the output of
the transformer?

No, you need another capacitor, with a steering diode, to provide the
Vcc for the op-amp But it's still more efficient. This supply also runs
your flip-flop.

3. The positive voltage is fed into the capacitor through a resistor so
that the current drawn from the transformer is very small. Charge time
is thus longer (one second or more), but it's not a problem for that
applicaton.

Correct.

4. The push button is depressed, the "logic" box connects the capacitor
to the first coil for a short time. During this time, the capacitor
discharges itself almost completely into the coil. This, to me, is
required because of the relatively high energy required to have the
coil operate.

Correct.

5. The capacitor loads itself again.

Correct.

6. The button is depressed a second time, the logic connects the
capacitor to the second coil of the relay, thus changing its position.

Ah, well, if you have a 2-coil relay, have two push-buttons and
eliminate the flip-flop. Saves energy (well, it uses your instead, but
you have plenty to spare).

What I have a hard time understanding is how a D-Type flip flop would
remember its previous state when the charge in the capacitor is gone,
thus reducing the voltage to almost nil.

See above; you have a second capacitor that isn't discharged.

--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[OBones]

John Woodgate wrote:

1. The step up transformer is used to get about 6Volts from the 1V
audio signal. That's fine. Out of curiosity, could this be replaced by
a diode voltage multiplier?

No.

Fair enough, that's what I thought.

2. The diode bridge is used to make this into a positive voltage. This
could be replaced by op amps as you suggested. But where do these get
the VCC-VSS from? Directly from their own regulation of the output of
the transformer?

No, you need another capacitor, with a steering diode, to provide the
Vcc for the op-amp But it's still more efficient. This supply also runs
your flip-flop.

Ah, that's the trick. I should have thought about that.
However, could you explain why 4 diodes in a bridge configuration are
less efficient than the opamp solution? Is it because of the cumulated
dropout voltage? (about 1.4v, if I'm correct)

6. The button is depressed a second time, the logic connects the
capacitor to the second coil of the relay, thus changing its position.

Ah, well, if you have a 2-coil relay, have two push-buttons and
eliminate the flip-flop. Saves energy (well, it uses your instead, but
you have plenty to spare).

That's right, but after having thought about the flip flop idea, it
seems to me that I can simply plug the coil of the latching relay
accross Q and /Q as those outputs are rated for +-50mA as indicated in
the datasheet (example) here:

http://www.onsemi.com/pub/Collateral/NL17SZ74-D.PDF

and the relay is around 25mA.
But doesn't this permanently draw 25mA from the supply, and hence put a
big stress on the audio line?

Cheers
Olivier

 

[John Woodgate]

I read in sci.electronics.design that OBones
<obones_gfd_@_gfd_altern.org> wrote (in
<d4j19f$p0g$1@reader1.imaginet.fr&gt about 'Line powered audio switch, is
this feasible ?', on Mon, 25 Apr 2005:

Ah, that's the trick. I should have thought about that.
However, could you explain why 4 diodes in a bridge configuration are
less efficient than the opamp solution? Is it because of the cumulated
dropout voltage? (about 1.4v, if I'm correct)

Yes, and the op-amp gain helps too; it overcomes the 'bottom-bend' of
the diodes at low input voltages.

[snip]

That's right, but after having thought about the flip flop idea, it
seems to me that I can simply plug the coil of the latching relay
accross Q and /Q as those outputs are rated for +-50mA as indicated in
the datasheet (example) here:

http://www.onsemi.com/pub/Collateral/NL17SZ74-D.PDF

and the relay is around 25mA.
But doesn't this permanently draw 25mA from the supply, and hence put a
big stress on the audio line?

So don't do that!
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[OBones]

John Woodgate wrote:

Ah, that's the trick. I should have thought about that.
However, could you explain why 4 diodes in a bridge configuration are
less efficient than the opamp solution? Is it because of the cumulated
dropout voltage? (about 1.4v, if I'm correct)

Yes, and the op-amp gain helps too; it overcomes the 'bottom-bend' of
the diodes at low input voltages.

Understood.

and the relay is around 25mA.
But doesn't this permanently draw 25mA from the supply, and hence put
a big stress on the audio line?

So don't do that!

Fair enough, I've put a schematic together, which I think might work.
However, I would appreciate anyone's input wether it is ok or not.
Here is the URL:

http://obones.com/index.php?module=article&view=7

Thanks a lot for your effort and support.