[time-nuts] RS 232

[Mark C. Stephens]

Although your description,
" 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." Is a perfect circuit description, I'd be more confident with a schematic :)


--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: Friday, 26 July 2013 5:32 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] RS 232

I do not understand your question, I am referring to low noise applications  like counters for dual mixers or other AV measurements, but also Shera and even  Tbolt where external noise should be kept to a minimum. When you chase 1 E-14,  isolation is key and I always like to err on the cautious side and as I stated  we use blue tooth or USB but in the case of USB there are always H11 in the  circuit. Some still like to use RS 232 and the subject came up and I have on my  boards H11's like on the counter Corby uses but he ended up using an external  power source and I like to eliminate that requirement. David had the right  answer using the power that the RS 232 mouse uses out of a DB 9, started looking  but I do not have one any more and I can not find any data.
Bert
 
 
In a message dated 7/25/2013 2:48:43 P.M. Eastern Daylight Time, marks at non-stop.com.au writes:

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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