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, ewkeh...@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, > r...@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-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of ewkeh...@aol.com >> Sent: Friday, 26 July 2013 5:32 AM >> 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. > > <H11 opto.pdf> > _______________________________________________ > 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.