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'[PIC]: Making a Audio Switcher'
2005\04\16@142820 by L030010

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Hi all

Need some advise in now to design an audio switcher

This switch programmable and can route the sound signal to the correct
speaker .

regards

2005\04\16@145854 by Jose Da Silva

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On April 16, 2005 11:28 am, L030010 wrote:
> Hi all
>
> Need some advise in now to design an audio switcher
>
> This switch programmable and can route the sound signal to the
> correct speaker .

If you don't want to hear clicking sounds as you switch from one speaker
to the next, you will need to have a variable resistance between the
speaker and the output going from infinite (open) resistance to zero
resistance (closed circuit).
One clever design did it by making a light box using photosensors and a
light moving on a track, which is a very mechanical way of doing it,
but it works and is easy to fix.

2005\04\16@175623 by Vern Jones

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For switching ahead of the amplifier, I use FET switches for the Audio. It
takes a junction FET to do the job. If the right resistances and capacitor
sizes are used on the Gate, the switching is very smoth without clicks and
pops. If you are switching on the speaker side, then HIGH Current AC devices
must be used, easiest are relays, but are not smooth switching devices. I
havent used a power FET, but it could possibly work.

I have drawings for the FET switches if anyone is interested.

Vern
----- Original Message -----
From: L030010 <spam_OUTl030010TakeThisOuTspamsingnet.com.sg>
To: Microcontroller discussion list - Public. <.....piclistKILLspamspam@spam@mit.edu>
Sent: Saturday, April 16, 2005 11:28 AM
Subject: [PIC]: Making a Audio Switcher


> Hi all
>
> Need some advise in now to design an audio switcher
>
> This switch programmable and can route the sound signal to the correct
> speaker .
>
> regards
>
> -

2005\04\17@045414 by L030010

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Hi Vern

may i have a look at the diagram?

regards
Soon Lee


WebSite : http://soonlee.agreatserver.com
{Original Message removed}

2005\04\17@101423 by L030010

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part 1 2057 bytes content-type:text/plain; (decoded 7bit)

Please comment on this  design i have

the design my not make sense as i am not electronic trained


WebSite : http://soonlee.agreatserver.com
{Original Message removed}

2005\04\17@152623 by Jose Da Silva

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On April 17, 2005 07:14 am, L030010 wrote:
> Please comment on this  design i have
> the design my not make sense as i am not electronic trained

The transistors are biased to 0v to turn them off (open circuit),
otherwise they are biased to 5v to turn them on (closed circuit).

The speaker should use a reverse biased diode across it (similar to
relays), otherwise your circuit needs to guarantee that you will quiet
the speaker before/after use.

2005\04\18@082606 by Gerhard Fiedler

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L030010 wrote:

> Please comment on this  design i have
>
> the design my not make sense as i am not electronic trained

AFAIK pretty much all speaker drivers drive the speakers with AC, with
(ideally) 0 V DC component. How exactly that is generated depends on the
final amp stage. Your switch circuit seems to assume a non-0 V DC
component.

You weren't clear about whether you want a pre-amp switcher or a post-amp
switcher. This looks like a post-amp switcher, for amplifiers with little
power. As it is, it wouldn't work with the bipolar currents that a speaker
driver will generate. You would probably have to make a circuit like what
is inside a 4066 that can stand the currents you need. It is /much/ easier
to switch on the input side of the amp (unless you use relays to switch the
outputs).

Maybe you tell more about your objective, to get some ideas.

Gerhard

2005\04\18@095854 by L030010

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Thanks for the input

actually i am looking at tapping the signal from the PC sound card, switch
it to one of 10 speakers I have  and then to the speaker. if the signal
after the switch is too weak i got no problem to ampify the signal


please advise me on this as i am not relly an audio and electronic guy

many thanks

Regards

WebSite : http://soonlee.agreatserver.com
{Original Message removed}

2005\04\18@125803 by Martin McCormick

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"L030010" writes:
>Thanks for the input
>
>actually i am looking at tapping the signal from the PC sound card, switch
>it to one of 10 speakers I have  and then to the speaker. if the signal
>after the switch is too weak i got no problem to ampify the signal

       Someone else on this list gave you the advice of using a
circuit like the FET's in a CD4066 quad bilateral switch.  This is
excellent advice and will definitely switch the output of your sound
card as long as it is the kind that doesn't have a power amp output to
a small set of speakers.  The SB16 card, for example, has a
thumb-wheel volume control on the back plane and it will actually feed
audio to small speakers that do not have their own amplifiers.  The
amp on the sound card is probably a Watt or two.

       Don't use a CD4066 on that because they do have internal
resistance that would probably make the sound output too low.

       Most of the modern sound cards send a line-level output to the
audio jacks and that should be in the 2 or 3-volt range like the
output of a piece of hifi gear.

       If you build your switcher so that the 4066's have a VDD of 15
volts or even 12 volts, audio peaks will not leak through the switch
unless they exceed plus or minus half the VDD, only referenced to
ground.  In other words, audio peaks would have to be at +-6 volts in
order to break through if you use 12 volts for VDD on the 4066's.

       Of course, if you use a PIC for your controller, this means
you'll have to have a level converter between the output of the PIC
and the control lines on the 4066 gates.

       You can use 5 volts VDD on the 4066, but audio peaks of +-2.5
volts are sufficient to start coming through the switch even when it
is off.

       You will definitely need amplified speakers at each location.
They can be any kind of speaker that has a line-level audio amplifier,
from a really good sound system down to the cheapest amplified P.C.
speakers you can find.

       If there are any distances involved, you might want to use
shielded audio cables since you can pick up mains hum.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Information Technology Division Network Operations Group

2005\04\19@080117 by Gerhard Fiedler

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Martin McCormick wrote:

>>actually i am looking at tapping the signal from the PC sound card, switch
>>it to one of 10 speakers I have  and then to the speaker. if the signal
>>after the switch is too weak i got no problem to ampify the signal
>
> Someone else on this list gave you the advice of using a circuit like
> the FET's in a CD4066 quad bilateral switch.  

That would have been me :)

> This is excellent advice and will definitely switch the output of your
> sound card as long as it is the kind that doesn't have a power amp
> output to a small set of speakers.  The SB16 card, for example, has a
> thumb-wheel volume control on the back plane and it will actually feed
> audio to small speakers that do not have their own amplifiers.  The amp
> on the sound card is probably a Watt or two.
>
> Don't use a CD4066 on that because they do have internal resistance that
> would probably make the sound output too low.

Given that you said you weren't opposed to using an amp after the switch, I
think using the 4066, possibly with a resistor divider in the input, and an
amp afterwards is probably the easiest solution. Look into app notes for
the 4066; you'll probably find circuits like this (without the input
attenuator, though).

Gerhard

2005\04\19@111746 by L030010

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Hi Gerhard

can you kindly enlighten me a bit more on the following

"possibly with a resistor divider in the input, and an amp afterwards is
probably the easiest solution."
what is ment by a resistor divider in the input?

sorry I am not a electronic trained guy

please advise

Regards

WebSite : http://soonlee.agreatserver.com
{Original Message removed}

2005\04\19@115341 by Martin McCormick

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Gerhard Fiedler writes:
>That would have been me :)

>Given that you said you weren't opposed to using an amp after the switch, I
>think using the 4066, possibly with a resistor divider in the input, and an
>amp afterwards is probably the easiest solution. Look into app notes for
>the 4066; you'll probably find circuits like this (without the input
>attenuator, though).

       I started playing around with the CD4016 and the CD4066 in the
late seventies and those are the first chips I go to if I want to
switch audio since the input and output terminals pass AC as long as
the peaks are below VDD/2.  I probably shouldn't admit this in public,
but I have been known to connect a pot as that divider you mentioned
and then turn the gate off while cranking up the pot until I hear the
clicks and pops of the audio peaks breaking through the switch.  I
don't know how close I am to blowing the FET's, but I then back it
down a bit until there is silence.

       I haven't blown one that way yet.  Be patient, though.  There
isn't a McCormick-proof chip on the planet.

       If you need to switch more signals, there are some similar
chips with one-of-N type functionality, I think.  They are multiplex
encoder/decoders, just the thing for the outputs of a PIC to control.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Information Technology Division Network Operations Group

2005\04\20@070706 by Gerhard Fiedler

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L030010 wrote:

> can you kindly enlighten me a bit more on the following
>
> "possibly with a resistor divider in the input, and an amp afterwards is
> probably the easiest solution." what is ment by a resistor divider in
> the input?
>
> sorry I am not a electronic trained guy

Take for example the 4052; this is a dual 4-channel analog (de)multiplexer.
Meaning it serves to connect one input to four outputs, or one output to
four inputs (your case) -- and this two times (like with stereo signals).
Of course, whether this is exactly the configuration that serves your need,
I don't know; you'll have to think about how you want to control those
switches and research the available circuits that have elements similar to
this one.

Now you need to see what voltage your sound card puts out. This is probably
in the range of +- 12 V max; you can measure this. Then you have to decide
how you want to supply the chip; a dual supply would be good (because then
you won't have to deal with shifting the AC input). It stands max. +-7.5V,
maybe you can use the +-5V from the computer supply.

This means that you have to divide the input voltage so that it doesn't
exceed the chip's supply voltage (or stays a bit below it). Say you want to
divide it by 3. Then you use two resistors, one double the size of the
other:

in ------ R1 ----+----- out (to chip input)
                |
               R2
                |
               gnd

R1 would be double the size of R2. Maybe R1=220R and R2=100R.

You probably should read up on some electronics introduction (sorry, but I
don't have any pointers to online material) to get a rough understanding of
this all while experimenting with it.

Gerhard

2005\04\20@083230 by L030010

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ok thanks for your help the description you have made is great

thanks
WebSite : http://soonlee.agreatserver.com
{Original Message removed}

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