On 4/30/06, alan smith <micro_eng2@yahoo.com> wrote:
> Hmmm...I've opened a can of worms on this one!  My spec was revised...I can run this at 3V now, and I don't need to talk over 500M, less than 1M typical to some "unknown/undefined" device, but just RS232.  I found that TI makes some Maxim clone parts, looking at those now.
>
> Vasile Surducan <piclist9@gmail.com> wrote:  On 4/29/06, andrew kelley wrote:
> > On 4/21/06, Vasile Surducan
> wrote:
> > > On 4/20/06, alan smith wrote:
> > > > nope...has to be real RS232 levels.....interfacing with unknown devices, but they will assume 232 levels.
> > >
> > > Then forget it. There is no 2.5V part which is producing with charge
> > > pump a *true* RS232 level. Even the 3V part (ie MAX3232) does not
> > > produce a *true* RS232 level. Maybe you should define first which is
> > > the RS232 true level ?
> > >
> > > greetings,
> > > Vasile
> >
> > No 2.5V part? There should be since, rs232 levels are (from memory)
> > from +-3v to +-27v respsectively.
>
> +-3V on the receiver side. Use any MAX3232 or clone, supply it on 2.5V
> and try to communicate over 500m of cable with a PC. If you can, I'll
> buy you a beer, the best ameican one (yacksss...).
>
> greetings,
> Vasile
>
>
> A voltage doubler would accomplish
> > +5v and a voltage doubler on the negative side could put out also a
> > -5v.. So I don't see why there isn't a 2.5v part, or at least one
> > that could be made using suitable voltage doubler chips.

A doubler will works ok with small load. As long the cable will  be,
as high the parasitical capacitance. Adding the receiver load (which
could be less than 7K) and surprise, there will not be 5V as expected
but much less.
One example is the MAX232. Supplied at +5V you should get +/-10V right ?
You'll get +/-8V in the best circumstance with a standard load.
So the theory is one and the practice is else.


greetings,
vasile

> >
> > andrew
> >
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
>
>
> ---------------------------------
> Yahoo! Mail goes everywhere you do.  Get it on your phone.
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist