CarBytes - MAX232 circuit

[Eric Clark]

On Wed, 10 Nov 1999, Peter Gargano wrote:

> Carsten's change to MAX232 circuit...
> 
> Andrew K. Mattei wrote:
> > 
> > >one question, What is the difference betwee Andrew Mattei's and Carsten
> > >Meyer's?  I planned on building Carsten's design because its more simple.
> > >What do the four transisters in the circuit?
> > 
> > I'll field this one.
> > 
> > Carsten's design is dependent on the characteristics of the diode in the
> [snip]
> 
> In fact the latest incantation of Carstens interface uses a MAX232
> and a resistor and diode to combine the Tx and Rx ALDL TTL voltages.
> Carsten's original circuit had two transistors and a zener (diode),
> and I think that is was a problem, as the zener's voltage may have to be
> selected for the particular vehicle - anyway, he didn't think it was such 
> a good idea (probably got too many emails asking why it didn't work!).
> 
> So, are the transistors necessary (in Andrew's)? I suspect not (but I have 
> not built either of these circuits) - I was just clarifying the confusion.

My only question about the transistors vs the diode, is whether Carstens
MAX232 design will invert? the data stream.  I am hoping that its
functionally equivalent to Andrews so I can use the LT1_Edit software with
my own interface.  It looks like I'm going to have to substitute smaller
caps because Maxim sent me two MAX232ACPE's instead of MAX232CPE's for
free samples.

-Eric