[time-nuts] RS 232

[EWKehren at aol.com]

Diagram of the two opto couplers?
 
 
In a message dated 7/25/2013 4:10:54 P.M. Eastern Daylight Time,  
paulswedb at gmail.com writes:

Bert  pretty sure he is just asking for a diagram. He is interested in the
method  of noise isolation.
Regards
Paul.


On Thu, Jul 25, 2013 at  3:32 PM, <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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