[time-nuts] RS 232

[Mark C. Stephens]

Hi Bert,

I am sure your circuit is clear in your head, but would you mind attaching detail?
You have perked my interest with the "low-noise" keyword ;)


-marki

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of EWKehren at aol.com
Sent: Thursday, 25 July 2013 11:39 PM
To: time-nuts at febo.com
Subject: [time-nuts] RS 232

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
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