[time-nuts] RS 232

[EWKehren at aol.com]

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