[time-nuts] RS 232

[Bob Stewart]

I made the second on on this page some years ago and somehow it manages to survive the junk box.  It only uses 2 transistors and 4 resistors and doesn't require an external power source.  It it feeds the negative voltage through from the TD pin, so I don't think it can be used on full duplex.  Of course you could probably add a diode and a supercap and fix that deficiency.

http://www.scienceprog.com/alternatives-of-max232-in-low-budget-projects/

Bob - AE6RV





>________________________________
> From: "EWKehren at aol.com" <EWKehren at aol.com>
>To: time-nuts at febo.com 
>Sent: Thursday, July 25, 2013 3:34 PM
>Subject: Re: [time-nuts] RS 232
> 
>
>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
>>_______________________________________________
>>time-nuts  mailing  list -- time-nuts at febo.com To unsubscribe, go to  
>>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>and  follow the  instructions   there.
>>
>>
>>_______________________________________________
>>time-nuts   mailing list -- time-nuts at febo.com
>>To unsubscribe, go to  
>>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>and  follow the  instructions  there.
>>
>>_______________________________________________
>>time-nuts  mailing list -- time-nuts at febo.com
>>To unsubscribe, go to  
>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>and follow the  instructions there.
>>
>>  
>>
>
>_______________________________________________
>time-nuts  mailing list -- time-nuts at febo.com
>To unsubscribe, go to  
>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the  instructions there.
>
>_______________________________________________
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.
>
>
>