I believe the trend for the last 10 years has been to use a positive threshold. I mess with serial ports all the time professionally and not and I do not remember the last time I saw one that did not work with a positive threshold.
Didier KO4BB Bob Camp <[email protected]> wrote: >Hi > >The gotcha with "standard" RS-232 is that the range from -3 to +3 volts >is defined as "undefined". In other words, a negative should be below >-3V and a positive should be above +3 volts. Indeed most (but not all) >chips count zero as a negative. A few have hysteresis and others have >some odd thresholds. > >Bob > >On Jul 26, 2013, at 12:14 PM, Angus <[email protected]> wrote: > >> Hi, >> >> #5 is one of the reasons I preferred not to take the signal negative. >I suppose it depends on the situation, but for the spitting data into a >pc I used to find that a 0 to 5v or so signal powered from a control >line almost always worked. The most common problem was either a faulty >com port or an optocoupler circuit that did not have enough gain to >pull the line close to 0v. ( that was a while ago though - not so much >'legacy' as 'vintage'! ) >> >> Angus. >> >> >> From: "Bob Camp" >> To: "Discussion of precise time and frequency measurement" >> Sent: July 26, 2013 1:37 PM >> Subject: Re: [time-nuts] RS 232 >> >> Hi >> >> In order to get voltages from the other pins on the D connector: >> >> 1) You have to program them to be in the "correct" state (either high >or low) >> 2) They have to be present on the "driver" side (usually, but not >always true) >> 3) They need to be > 3 V (diode drops etc…) >> 4) They need to supply enough current (as in no isolating resistors, >usually true) >> 5) You need to have two of them to spare that meet these criteria >(one positive and one negative) >> >> Its a little like rolling dice, sometimes it will work, sometimes it >won't work. >> >> Bob >> >> On Jul 26, 2013, at 7:01 AM, [email protected] 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, >>> [email protected] 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: [email protected] >[mailto:[email protected]] On >>> Behalf Of [email protected] >>>> Sent: Friday, 26 July 2013 5:32 AM >>>> To: [email protected] >>>> 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, >>> [email protected] 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: [email protected] >[mailto:[email protected]] On >>>> Behalf Of [email protected] >>>> Sent: Thursday, 25 July 2013 11:39 PM >>>> To: [email protected] >>>> 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 -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
