[time-nuts] RS 232

[wb6bnq]

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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