[time-nuts] RS 232

EWKehren at aol.com EWKehren at aol.com
Thu Jul 25 22:55:51 UTC 2013


Contact me off list and I will make a scetch
 
 
In a message dated 7/25/2013 6:34:58 P.M. Eastern Daylight Time,  
marks at non-stop.com.au writes:

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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