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'analog switch'
1999\07\12@093837 by engelec

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Hi to all engineers.
last night I made a small circuitry to mute the analog line
the pic part works ok  but analog section didn't work at all.
on output when I add 10k pull up resister works fine but I can't
do that on audio line.
I connected pic with max4066 analog chip. the problem
I found is that 4066 needs voltage on output  to operate
which we do not have it my question is this is  there any part that can
be used to mute the analog line "audio" beside relay ?
any help will highly appreciated.

Andre

1999\07\12@102122 by Dave VanHorn

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> I connected pic with max4066 analog chip. the problem
> I found is that 4066 needs voltage on output  to operate
> which we do not have it my question is this is  there any part that can
> be used to mute the analog line "audio" beside relay ?
> any help will highly appreciated.



You can use the 4066, you just have to follow the rules.
The signal voltage must always be inbetween the supply voltages. I'm betting
you used only 0V (ground) and +5V.  If you run a line level signal into
this, you'll find horrible distortion, because the analog voltage levels
are - (someting) to +(something)  It's the -(something) part that's getting
you in trouble.

Solution #1: Connect VEE to a low negative voltage, at least 1.5V, -5 would
be ideal.
Solution #2: Capacitively couple the signal in and out of the circuit, and
on the input side, use a pair of equal value resistors, say 10k, to bias the
4066 to 2.5V.

1999\07\12@110947 by Michael Rigby-Jones

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I have seen simple muting circuts using either a JFET or even a small
bipolar clamping the signal to ground.  The signal is passed through a
largish value resistor first.  This is used even on high end car stereos
systems like Kenwood and Alpine.

Regards

Mike Rigby-Jones

       {Original Message removed}

1999\07\12@111357 by Bob Blick

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Hi Andre,

The analog switch can only operate with analog voltages within its supply
rails. If your analog signal is 0 volts referenced it swings negative and
the analog switch cuts out. You can bias your analog signal as already
suggested.

Also you can use an NPN transistor(2N3904 or PN3904 works very well) to
short to ground the analog signal if the analog signal is less than .5
volts. Experiment with base resistors to reduce pop sound.

Cheerful regards,
Bob

1999\07\12@170558 by l.allen

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>         Hi to all engineers.
>         last night I made a small circuitry to mute the analog line
>         the pic part works ok  but analog section didn't work at all.
>         on output when I add 10k pull up resister works fine but I can't
>         do that on audio line.
>         I connected pic with max4066 analog chip. the problem
>         I found is that 4066 needs voltage on output  to operate
>         which we do not have it my question is this is  there any part that
> can
>         be used to mute the analog line "audio" beside relay ?
>         any help will highly appreciated.
>
>         Andre

A simple method is to use a light dependent resistor in the audio
line. The LDR is very high resistance when dark, so a no power-mute
would have the LDR in line with the audio followed by a lowish
(2k-10k) resistor to ground. An LED driven by the PIC could enable/
disable it (2 Meg dark to around 5K light).
I have seen this system used but I have not used it personally, I
dont think there would be any significant distortion being a resistive
device but I don't know how linear an LDR is.
The circuit I saw actually used 2 LDRs in a "T" attenuator . That is
in line LDR, resistor to ground, in line LDR.

Hope this helps.


Lance Allen
Uni of Auckland
New Zealand

1999\07\12@172454 by Richard Prosser

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I've seen this method in "vibrato" generators  and avc circuits etc. going
back well into the valve era. However, it would pay to match the wavelength
response of the LDR against the output from the LED. LDRs are, I think,
somewhat more sensitive to green light. ( = Use a green LED ?)

Richard

> {Original Message removed}

1999\07\17@161609 by p.cousens

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Sorry for the late reply !

I have used LDR's to mute analog signal lines.

I sandwich a grain of wheat lamp between two LDR's, ( stereo )
slide them into a rubber tube (2.5mm three core flex outer insulation
normally) and seal the ends with  black silicone

On the LDR's I use, the resistance varies from ~50 Ohms (light on)
to over 20 MOhms (light off).

I normally supply a second unswitched power source to the lamp
via a pot, so I can use it as a preset attenuator, not full mute.

The attack and decay characteristics of this setup are very pleasing.
The mute time is slow (like a record ending), the attack is a lot faster
but still very smooth ( ~ a quarter second ).

And of course the signal is completly isolated

Andre Abelian wrote:
{Quote hidden}

--
Peter Cousens
spam_OUTp.cousensTakeThisOuTspamcwcom.net

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