[time-nuts] RS 232

EWKehren at aol.com EWKehren at aol.com
Thu Jul 25 20:34:23 UTC 2013


Bill 
Thank you I am only looking for a solution that is simple in Corby's case  
we used a separate power source, but the question is, is it necessary. That 
is  why I brought it up to the list. Shopping for ideas.
Bert
 
 
In a message dated 7/25/2013 4:06:03 P.M. Eastern Daylight Time,  
wb6bnq at cox.net writes:

Hi  Bert,

My attitude is if you are going to provide an RS-232 port then do  it 
properly (min of +/- 3 volts & max of +/- 25 volts).  RS-232  is still a 
popular item in the hobby controller world, although USB is  gaining 
ground.  In so far as stability goes, RS-232 is much cleaner  and easier 
to handle in the micro coding compared to USB.  With that  said, there is 
nothing wrong with providing both, it just makes the coding  a bit 
harder.  If you need long lines and want common mode  suppression then 
utilize RS-485, a derivative of RS-232.

You could  also use TOSLINK, the fiber optic lines used in the audio 
field.  The  components are fairly cheap compared to other forms of 
plastic or glass  (more expensive) fiber products.  Most products will 
handle up to 5  MHz at reasonable distances.  If you are careful in 
selecting the TX  and RX port parts it can go up to 15 MHz at the top 
end, especially at  short distances.

Irrespective of all that, the power source has no  relationship to the 
RS-232 or USB for that  matter.

73....Bill....WB6BNQ

EWKehren at aol.com  wrote:

>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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