Hi I can't say if they were more than 10 years old or not, but I have seen some ports that do not work reliably with a 0-5V signal in the last few years.
Bob On Jul 26, 2013, at 3:58 PM, Didier Juges <[email protected]> wrote: > 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. _______________________________________________ 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.
