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: "ewkeh...@aol.com" <ewkeh...@aol.com> >To: time-nuts@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, >wb6...@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 > >ewkeh...@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, >>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. > >_______________________________________________ >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.