[time-nuts] RS 232

EWKehren at aol.com EWKehren at aol.com
Thu Jul 25 19:05:12 EDT 2013


on some of my projects some prefer to use RS 232 and I am not arrogant  
enough to say that RS 232 is not an option but try to help them and that was 
why  I asked the original question to make it for them as simple as possible. 
I  combine opto with USB but if you want to run 10 devices at the same time 
as one  time nut asked me about no one I asked had an answer.
Bert Kehren
 
 
In a message dated 7/25/2013 5:48:16 P.M. Eastern Daylight Time,  
john at miles.io writes:

Agreed,  nobody should be using RS232 for anything nowadays.  USB doesn't
seem  to cause noise problems in equipment that works at the -170 dBc/Hz  
and
below level (ahem) so it will be good enough for most other  sensitive
applications, assuming good design/layout practices are  followed.

USB support chip manufacturers have a lot of experience  supporting 
customers
who need their USB devices to pass FCC, CE, and other  worldwide EMI
standards.  There are a lot of good app notes and other  literature out
there.  As far as what components to use, I'd suggest  checking out
www.ftdichip.com if you're looking for the proverbial "path of  least
resistance."   You can't get much simpler than an  FTD232B.

-- john, KE5FX
Miles Design LLC


>  -----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, July 25, 2013 12:32 PM
> To:  time-nuts at febo.com
> Subject: Re: [time-nuts] RS 232
> 
> 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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