On 4/30/06, William Chops Westfield <westfw@mac.com> wrote:
> On Apr 30, 2006, at 7:33 AM, Vasile Surducan wrote:
>
> > try to communicate over 500m of cable with a PC.
>
> rs232 isn't spec'ed for 500m of cable.

are you sure ? which specs do you have ?

  IIRC, it has specs like:
> 1) maximum speed 19200
> 2) 19200 has a cable length limit of about 20 feet.
> 3) "HW flow control" doesn't exist.
> 4) a rather complex set of modem signal exchanges is REQUIRED.
>
> In short, rs232 is one of the widely and flagrantly violated
> specifications in the history of electronics.  Go ahead and stick
> a driver designed for 3.3V in your 2.5V circuit and see if it
> works.   Measure it, see if you feel comfortable with the output.
> If you're felling adventuresome, try it at various speeds
> and cable lengths with various remote ends, and figure out what
> the limits are, and then tell us...
>
> Alternately, the market is full of inductor based voltage converters
> that will boost 2.5V to 5V (or higher), thanks to the desire to
> power 5V logic from batteries.  You might even save money using
> something like Blick's 3T boost regulator to drive old-fashioned
> multi-supply driver chips...
>
> (cisco has an 16/32 port rs232 async card that uses 5V driver
> chips (16 or 32+ of them.)  Groan.  I don't know what they were
> thinking.  (of course, it does NOT exhibit the infamous "break
> problem", so perhaps that's what they were thinking...))
>
> BillW
>
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