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PICList Thread
'using I/O as switch & thanx...'
1999\01\06@225838 by synergetix

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Quick thanx to all those which replied, kindly, to my posted question.
Almost as good as Macrosoft's tech support ;-)

I need to use a PIC I/O line as a simple SPST switch, but I would rather
use something lighter than a relay.  Would a 4066 work?  If so, is there
any interfacing circuitry required between the CMOS and the PIC?  (I'd
rather ask before blowing any more parts, as my electronic habit is
driving me into debt)

                               Thanx again,

                                               Synergetix

1999\01\07@034632 by ebos

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synergetix@HOME.COM wrote:

> Quick thanx to all those which replied, kindly, to my posted question.
> Almost as good as Macrosoft's tech support ;-)
>
> I need to use a PIC I/O line as a simple SPST switch, but I would rather
> use something lighter than a relay.  Would a 4066 work?  If so, is there
> any interfacing circuitry required between the CMOS and the PIC?  (I'd
> rather ask before blowing any more parts, as my electronic habit is
> driving me into debt)
>
>                                 Thanx again,
>
>                                                 Synergetix

No,

Try the 74HC4066
It works fine for me.

Eduard Bos

1999\01\07@062024 by paulb

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synergetix@HOME.COM wrote:

> I need to use a PIC I/O line as a simple SPST switch, but I would
> rather use something lighter than a relay.  Would a 4066 work?

 Equivalent circuit of a 4066 is approximately a contact in series with
a 150 ohm resistor.  It isn't entirely linear either.  For a 74HC4066, I
think it's nearer 50 ohms (I suppose I could look it up at:
http://www.st.com/stonline/books/pdf/docs/1968.pdf - Yep, it *is* 50
ohms nominal ).

> If so, is there any interfacing circuitry required between the CMOS
> and the PIC?  (I'd rather ask before blowing any more parts, as my
> electronic habit is driving me into debt)

 No interface - as long as you only wish to switch voltages within the
5V supply voltage range you are using for both.  Actually, I am
surprised to find the Signetics "HC" part is rated to 12 volts; but to
use that you have to switch with 12V CMOS logic; would require level
conversion from a PIC.
--
 Cheers,
       Paul B.

1999\01\07@074953 by Harrison Cooper

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face
Depends on what you are trying to switch. Analog or digital?  If its analog,
there are several good vendors (maxim for one) that make these.
Digital....should work fine, but this is a 4 channel device, so might as
well just use a NPN transistor (smaller & cheaper)

1999\01\07@145421 by John Payson

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> If so, is there any interfacing circuitry required between the CMOS
> and the PIC?  (I'd rather ask before blowing any more parts, as my
> electronic habit is driving me into debt)

|  No interface - as long as you only wish to switch voltages within the
|5V supply voltage range you are using for both.  Actually, I am
|surprised to find the Signetics "HC" part is rated to 12 volts; but to
|use that you have to switch with 12V CMOS logic; would require level
|conversion from a PIC.

Many 4066 variants are rated for over 5 volts, and indeed they
are quite commonly used for general-purpose switching of signals
up to about 12 volts.

As for PIC interfacing, if you only need to control one 4066
switch, you could probably use port pin RA4 which is open-drain
and can handle over +5 volts.  Note that, per the current data
sheet erata, use of RA4 at voltages above 10 volts or so (read
individual erata sheets for details) may cause excessive device
wear; if you're running your 4066 off 12 volts, you may want to
control it with RA4, using e.g. a 47K pullup and a 220K pulldown
(wired to ground, to limit the voltage on that pin to about 9-10
volts).  Even with VDD at 12 volts, a 4066 will regard a 9-10 volt
input as a valid "high".

1999\01\07@150633 by Peter L. Peres

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Hello,

 I have been following this thread, and I'd like to add that there is a
member of the 4XXX CMOS family that allows voltages larger than 5V to be
switched with 5V logic signals. It is the 4051 which has a Vee connection.

 If there is a negative voltage in the circuit, or if the logic is
referenced to Vdd then analog signals within +5V and -5V of the digital
GND can be switched. I don't remember the Vee limit specs, the voltages
may be higher. The 4051 is a 8:1 analog multiplexer with enable.

hope this helps,

       Peter

1999\01\07@161338 by paulb

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John Payson wrote:

> Many 4066 variants are rated for over 5 volts, and indeed they
> are quite commonly used for general-purpose switching of signals
> up to about 12 volts.

 Of course the "original" 4066 was rated for 15 or 18V.  I was
referring to the "HC" variants which I had hitherto assumed used the
standard "HC" voltage range of 2 to 6V.  Even the 74HC4024 (Reference:
http://www.st.com/stonline/books/pdf/docs/1963.pdf ) has this voltage
range.  SGS-Thompson at least has made the (54)74HC4066 an exception.
--
 Cheers,
       Paul B.

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