[time-nuts] RS 232

Thu Jul 25 16:52:54 EDT 2013

Thank you Paul. This is exactly what I wanted to know, as I said I already  
use the opto couplers the only thing is where to get the power from for the 
 transmitting side and you answered that. I will not use it but some others 
may.  I will stay with opto USB.. 

In a message dated 7/25/2013 4:40:24 P.M. Eastern Daylight Time,  
paulswedb at gmail.com writes:

Bert
I will add back in here. The max232 has the internal  switching oscillator
and that makes the noise. But you know that. So an  external +/-supply
linear is cheap and simple. Full wave bridge and 2 caps.  No regulation
needed. Using your opto isolator provides complete noise and  electrical
isolation. Computers are nasty beasts especially when you grab  +/- power
from the rs232 port. Some one re-confirmed my thinking that the  rs 232 spec
was +/-3V for noise margin. I think thats about all there  is.
Sorry if I am misunderstanding your  need.
Regards
Paul
WB8TSL

On Thu, Jul 25, 2013 at 4:34 PM,  <EWKehren at aol.com> wrote:

> Bill
> Thank you I am only  looking for a solution that is simple in Corby's case
> we used a  separate power source, but the question is, is it necessary. 
That
>  is  why I brought it up to the list. Shopping for ideas.
>  Bert
>
>
> In a message dated 7/25/2013 4:06:03 P.M. Eastern  Daylight Time,
> wb6bnq at cox.net writes:
>
> Hi   Bert,
>
> My attitude is if you are going to provide an RS-232  port then do  it
> properly (min of +/- 3 volts & max of +/- 25  volts).  RS-232  is still a
> popular item in the hobby  controller world, although USB is  gaining
> ground.  In so  far as stability goes, RS-232 is much cleaner  and easier
> to  handle in the micro coding compared to USB.  With that  said, there  
is
> nothing wrong with providing both, it just makes the coding  a  bit
> harder.  If you need long lines and want common mode   suppression then
> utilize RS-485, a derivative of  RS-232.
>
> You could  also use TOSLINK, the fiber optic  lines used in the audio
> field.  The  components are fairly  cheap compared to other forms of
> plastic or glass  (more  expensive) fiber products.  Most products will
> handle up to  5  MHz at reasonable distances.  If you are careful in
>  selecting the TX  and RX port parts it can go up to 15 MHz at the  top
> end, especially at  short distances.
>
>  Irrespective of all that, the power source has no  relationship to  the
> RS-232 or USB for that  matter.
>
>  73....Bill....WB6BNQ
>
> EWKehren at aol.com   wrote:
>
> >I do not understand your question, I am referring  to low  noise
> applications
> > like counters for dual  mixers or other AV  measurements, but also Shera
> and
>  >even  Tbolt where external noise  should be kept to a minimum.  When you
> >chase 1 E-14,  isolation is  key and I always  like to err on the 
cautious
> side
> >and as I   stated  we use blue tooth or USB but in the case of USB there
>  are
> >always H11 in the  circuit. Some still like to use RS 232  and the  
subject
> came
> >up and I have on my   boards H11's like on the  counter Corby uses but he
> >ended up  using an external  power  source and I like to eliminate  that
> >requirement. David had the  right  answer using the  power that the RS 
232
> mouse uses
> >out of a  DB 9,  started looking  but I do not have one any more and I 
can
>  not
> >find any data.
> >Bert
> >
>  >
> >In a message dated  7/25/2013 2:48:43 P.M. Eastern  Daylight Time,
> >marks at non-stop.com.au writes:
> >
>  >Hi   Bert,
> >
> >I am sure your circuit is  clear in your head, but would  you mind
> attaching
>  >detail?
> >You have perked my interest  with the "low-noise"  keyword   ;)
> >
> >
> >-marki
>  >
> >-----Original  Message-----
> >From:   time-nuts-bounces at febo.com  [mailto:time-nuts-bounces at febo.com]  
On
> >Behalf Of   EWKehren at aol.com
> >Sent:  Thursday, 25 July 2013 11:39 PM
> >To:    time-nuts at febo.com
> >Subject: [time-nuts] RS 232
>  >
> >Since  joining time  nuts over four years ago I  have not used a  single
> MAX
> >232 chip. Two   reasons MAX do not give me isolation and do  generate
>  noise
> >in critical  applications. I prefer the use  of  two H11 opto couplers
> which
> >work  perfect. On  the  receiving end the diode along with a current
> limiter
>  >and   blocking diode for the negative level works perfect. On  the 
output
> side
> >a  power  source is needed. If  one uses an USB adapter it  does have 
the +
> 5
> >volt  which  again works perfect.   How ever many prefer to use RS  232
> >direct and that is  why  I hope to get some comments  and suggestions 
from
> the
> >list. Corby  used on  our  counter circuit that he described a separate
> power
>  >source.
> >Present MAX circuits use a + 1.4 volt threshold   but   considering 
legacy
> >the question is what should  the  voltage swing be to make  it  
compatible
>  for
> >most PC's and  what options exist to get the  necessary  voltage. In  the
> past
> >other pins on  the RS 232 port where an ideal power  source. Still  an
>  option?
> >Bert   Kehren
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