[time-nuts] RS 232

[EWKehren at aol.com]

But do you get the speed
 
 
In a message dated 7/26/2013 10:41:02 A.M. Eastern Daylight Time,  
cfharris at erols.com writes:

I have  enclosed a sketch of the usual way of using opto's to make an
RS232 like  interface.  I haven't spent much time thinking, so I am sure
that I  have a few things backwards, but you should get the gist of how
it is  done.

It is only RS232 like because it has only a single  threshold.

-Chuck Harris



Rex wrote:
> FWIW, it was  clear as mud for me too.
>
> Bert began with, "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."
>
>  From that I took that he was doing RS232  using opto isolators. That 
implies + and -
> voltages to me. Where do  they come from and where are they relative to 
the isolation
> boundary?  If the goal is really isolation, how do these supplies get 
isolated? If  the
> noise is cured by isolation, these details seem important as the  
supplies need
> isolation too. Maybe the switcher in the MAX232 is  causing the noise. 
Then how do we
> get a negative supply from, say, +5V  without the noise? Then, maybe he 
was saying
> RS232 sucks and this  other way (not RS232 compatible) works better.
>
> The word  picture of Bert's solution, which provided more details, left 
me less  much
> less than clear too. Maybe I'm just not up on circuit shorthand  
terminology enough to
> follow what sort of current limiter is limiting  what current to what, 
and what is
> being blocked by a diode from which  negative level. Not really sure if I 
even got the
> big picture of what  he is describing. Is it an isolated equivalent of a 
MAX232
> interface  or something else that wouldn't talk to an RS232 device?
>
> So,  more clarification, or possibly that picture (~= 1k words) might 
help. Or  maybe
> I'm just obtuse and everyone else is getting it. (Seems Marki  may also 
be in the
> confused  camp.)


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