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PICList Thread
'(OT) AC Signal Control'
1998\10\23@220116 by Starfire Zhu

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Hi, there!

Greetings to those who noticed this message.

Could you tell me the simplest way to control the AC signal? I mean I
want to switch the signal on or off with a I/O pin form my PIC. The
signal is kind of voice or low frequency. By the way, a solution with a
relay is not expected, there must be other ways....

Can anyone shed  a light to me?

Thanks in advance!

1998\10\23@230504 by Mark Willis

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Starfire Zhu wrote:
>
> Hi, there!
>
> Greetings to those who noticed this message.
>
> Could you tell me the simplest way to control the AC signal? I mean I
> want to switch the signal on or off with a I/O pin form my PIC. The
> signal is kind of voice or low frequency. By the way, a solution with a
> relay is not expected, there must be other ways....
>
> Can anyone shed  a light to me?
>
> Thanks in advance!

 Knowing the voltage of the signal would help here (If it's reasonably
low voltage, an analog switch or the like would be a decent way to go.)
For example see the 74HC4016.  (Knowing more about the spceifics always
helps us help with a circuit.)

 I'm assuming your signal's under 50kHz or so from what you say <G>
Analog switches do have bandwidth limitations, and voltage range limits,
but pass voice & slow video without problems...  As always, read the
spec sheet, and as always, finding the right spec sheet to read is part
of the problem!  Some analog switches need bipolar supplies for AC
voltages (you could, with a 4016, capacitively couple input & output to
solve this, loosely dc biasing the Switch sides of the capacitors to
center them at Vcc/2, though.)

 I've used a logic-controlled Analog switch that controls pure AC
signals but it's late & I don't remember the part number tonight.
Anyone?

 Mark, spam_OUTmwillisTakeThisOuTspamnwlink.com

1998\10\24@120817 by Max Toole

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In a message dated 98-10-23 22:01:02 EDT, you write:

<< Could you tell me the simplest way to control the AC signal? I mean I
want to switch the signal on or off with a I/O pin form my PIC. The
signal is kind of voice or low frequency. By the way, a solution with a
relay is not expected, there must be other ways....
 >>
National Semi LM4862N is a 350 mw amp with a mute input that works great.

Max

1998\10\25@044113 by Radoni Calin

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Hi there !
   You do not like CD4066 ? (it contains 4 analog switches). If you are
interested I can give send you the specifications on monday or thursday.

Starfire Zhu wrote:

{Quote hidden}

1998\10\25@095230 by Mike Keitz

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On Sat, 24 Oct 1998 09:59:47 +0800 Starfire Zhu <.....zhuxhKILLspamspam@spam@CHEERFUL.COM>
writes:
>Hi, there!
>
>Greetings to those who noticed this message.
>
>Could you tell me the simplest way to control the AC signal? I mean I
>want to switch the signal on or off with a I/O pin form my PIC. The
>signal is kind of voice or low frequency. By the way, a solution with
>a
>relay is not expected, there must be other ways....

First there is a relay.  It works really well, but is hugely expensive
and large.  In a very few applications it is necessary.

Next down would be a CMOS switch such as a 4066.  These are handy if you
need several switches in the circuit.  Also there are the 4051, 4052, and
4053, which implement SPDT swtiches and multiplexers.  Even those are
overkill if you just need something real simple, like to mute a signal.
You'd only be using 1/4 of a whole IC to do this.  I'm sure I've seen
single COMS switches the size of SMT transistors.  Where to buy them
though?

I've used just an NPN transistor with no bias on the collector as an
audio muting control very successfully.  The collector is coupled to the
audio path through a capacitor.  When the base is driven with DC in the
usual way, the AC signal on the collector is shunted to ground.  The
signal has to be less than a few hundred mV peak to peak to keep from
being rectified by the transistor.

Multiplexers for audio can be built using diodes in series with the
signal paths.  One diode at a time is biased on.  Again, the signal has
to be small compared to the bias current to keep the diode from causing
too much distortion.  Even the, it will have some distortion.  Diode
swithching is used a lot in low-fidelity devices such as car radios and
communications equipment.

Both the transistor and diode methods are really cheap, but require
relatively large bias currents which would be undesirable in a micropower
design.

Finally of course a signal can be muted by upsetting the bias in an
existing amplifier stage.  This can also be used to power down the
circuit while muted.  The major problem is transient signals when muting
and unmuting.  Choosing the coupling capacitors as small as priactical
will help.  Also consider methods to keep the capacitors charged while
the circuit is powered down.


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1998\10\25@131636 by cousens

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> On Sat, 24 Oct 1998 09:59:47 +0800 Starfire Zhu <zhuxhspamKILLspamCHEERFUL.COM>
> writes:
> >Hi, there!
> >
> >Greetings to those who noticed this message.
> >
> >Could you tell me the simplest way to control the AC signal? I mean I
> >want to switch the signal on or off with a I/O pin form my PIC. The
> >signal is kind of voice or low frequency. By the way, a solution with
> >a
> >relay is not expected, there must be other ways....

One very simple way not mentioned yet, is to use a LDR
and a light bulb

I have made many remote controled faders using this setup
(local cafe's who don't have a disco licence get fined if the music is
too loud)
I use car alarm remote control (300mhz) units to turn on and off
a VERY small light(grain of wheat) bulb sandwiched between two LDR's
(stereo)
This way an employee standing outside/ across the road can lower
the music to a low level by pushing a button if they see the inspectors
comming down the street.

In my app a variable resistor also supplies power to the lamp
enabling the user to set the lower level(total mute not desired)

The atack is fairly fast though not disturbing and the decay is
almost like the end of a record, very smooth, your speakers
will love you,

I have only used LDR's on line signals (600ohms .5V)
and have had no problems.
Their resistance ranges from less than 30 ohms to over 20M ohms.
It takes around 4 seconds to reach 1M after removing the illumination,

--
Peter Cousens
email: .....cousensKILLspamspam.....her.forthnet.gr  phone: + 3081 380534
snailmail:  Folia, Agia Fotini, Karteros, Heraklion  Crete, Greece.

Is it true that they have, on the new version of windows
managed to increase the MTBF from 95 to 98 minutes ?
(That's why they called it 95)

1998\10\26@095420 by Brian Watson

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Starfire Zhu

The Farnell Electronics catalogue lists a pair of Optically Coupled
Bi-lateral Analogue FET switches.

They are each in a 6 lead DIL package described as:
Optocoupler with symmetrical bi-lateral photo-detector output, designed for
distortion free control of low level AC and DC analogue signals.

H11F1:  Isolation = 2500V, Breakdown = 30V, Ron = 200ohms, Roff = 300Mohms,
Ton/off = 15µsec, price = 2.28 pounds(UK) plus tax.
H11F3:  Isolation = 1500V, Breakdown = 15V, Ron = 470ohms, Roff = 300Mohms,
Ton/off = 15µsec, price = 1.62 pounds(UK) plus tax.

Brian Watson

{Original Message removed}

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