[time-nuts] RS 232

Fri Jul 26 12:25:00 UTC 2013

Any of the PC (native serial or USB/serial adapter) modem control lines can be used to get a positive or negative voltage. In your case look at pin 7.

See comments at the end of http://leapsecond.com/tools/comtick.c

/tvb
Sent from my iPad/mini

On Jul 26, 2013, at 4:01 AM, EWKehren at aol.com wrote:

> Since there is repeated request for the circuit se attachment. My question  
> is what can be done to get a positive voltage from some of the other unused 
> pins  of the DB 9 connector. What is needed is any where from 3 to 15 volt. 
> Diodes  work with 1 mA but I set Rx for 2 mA. Any thing else look at H11 
> data  sheet.
> Bert Kehren
> 
> 
> In a message dated 7/26/2013 4:06:37 A.M. Eastern Daylight Time,  
> rexa at sonic.net writes:
> 
> FWIW, it  was clear as mud for me too.
> 
> Bert began with, "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."
> 
> From that I took that he was  doing RS232 using opto isolators. That 
> implies + and - voltages to me.  Where do they come from and where are 
> they relative to the isolation  boundary? If the goal is really 
> isolation, how do these supplies get  isolated? If the noise is cured by 
> isolation, these details seem important  as the supplies need isolation 
> too. Maybe the switcher in the MAX232 is  causing the noise. Then how do 
> we get a negative supply from, say, +5V  without the noise? Then, maybe 
> he was saying RS232 sucks and this other  way (not RS232 compatible) 
> works better.
> 
> The word picture of Bert's  solution, which provided more details, left 
> me less much less than clear  too. Maybe I'm just not up on circuit 
> shorthand terminology enough to  follow what sort of current limiter is 
> limiting what current to what, and  what is being blocked by a diode from 
> which negative level. Not really  sure if I even got the big picture of 
> what he is describing. Is it an  isolated equivalent of a MAX232 
> interface or something else that wouldn't  talk to an RS232 device?
> 
> So, more clarification, or possibly that  picture (~= 1k words) might 
> help. Or maybe I'm just obtuse and everyone  else is getting it. (Seems 
> Marki may also be in the confused  camp.)
> 
> 
> 
> On 7/25/2013 3:34 PM, Mark C. Stephens wrote:
>> 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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