Agreed, nobody should be using RS232 for anything nowadays. USB doesn't seem to cause noise problems in equipment that works at the -170 dBc/Hz and below level (ahem) so it will be good enough for most other sensitive applications, assuming good design/layout practices are followed.
USB support chip manufacturers have a lot of experience supporting customers who need their USB devices to pass FCC, CE, and other worldwide EMI standards. There are a lot of good app notes and other literature out there. As far as what components to use, I'd suggest checking out www.ftdichip.com if you're looking for the proverbial "path of least resistance." You can't get much simpler than an FTD232B. -- john, KE5FX Miles Design LLC > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of ewkeh...@aol.com > Sent: Thursday, July 25, 2013 12:32 PM > To: time-nuts@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, > ma...@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-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of ewkeh...@aol.com > Sent: Thursday, 25 July 2013 11:39 PM > To: time-nuts@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@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@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@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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
