[time-nuts] RS 232

[paul swed]

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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