Captured message thread on the subject of ring detecting for the model 100: Fm: Cris Agnew 72245,731 To: All Has anybody built the ring detector featured in the Portable 100 Magazine (Feb '86 issue)? Does it really work? I'm asking because my M102 is still under warranty and I wonder if it really works as stated, and if it has proved its usefulness for people who need auto-answer that the M100/102 lacks. * Replies: (2) Fm: Eiji Miura 76703,4311 Cris, I have a ring detection cable (I did not make it), and it works with my M100. I believe modification is made on a modem cable, so you may not need to change anything inside the T102; therefore, you don't have to worry about warranty. Fm: Cris Agnew 72245,731 Eiji, where can I find this ring detection cable that you have? Fm: Eiji Miura 76703,4311 Cris, There used to be a company who was selling already-built ring detection modem cable with software, but they are not selling it any more. You probably have to do the modification yourself. We have some files on the subject in DL. See TELECO.DO and SCHEM.REV in DL 8. Fm: Tony Anderson 76703,4062 Yes, a number of folks have built the ring detector circuit from Portable 100, which was only one of several articles describing the technique. It works, and that's what you want, isn't it? Since it is external to the computer, it doesn't affect your warranty in any way. Personally, I'd prefer buying an external modem that had the auto-answer capability, along with 300/1200 baud operation. You have no idea how 1200 baud will affect your use, until you get hooked on it. Fm: Cris Agnew 72245,731 Well, yes that is what I'd like to know. I ran into a problem today. Radio Shack discontinued the Optoisolator which I need but now I'd do a little shopping around. I have trouble understanding what is an optoisolator and how it works and since it is no longer carried by RS, what other optoisolator will work? Is optoisolator and opto coupler the same thing? Also, I am a little confused on the schematic and I wonder if I actually have to wire the black/yellow wires from the phone line to pin 8 and 2? I really need help in clarifying this before I actually start construction. I know the benefit of having a 1200/300 external modem but again - money is a problem right now. So, I'll just use this ring-detector until I can afford an external modem. Fm: Tony Anderson 76703,4062 Optoisolators are pretty much interchangeable, as long as you don't exceed input voltage marked on the package. While Radio Shack discontinued the original one, the one that they currently stock will work just as well. Optoisolators are discrete devices which can be used to isolate two circuits, while coupling the signal from one to the other. In this case, it prevents telephone ringing voltage from reaching your computer. How it works: There is a little tiny light bulb in one end, and a photo cell in the other. When the bulb lights up, the photo cell concucts current. (More or less...) Exact design philosophy is a bit beyond our scope here. Optoisolator and optocoupler are two ways of saying the same thing.... the "coupler" "isolates". Black and yellow wires in telephone cables are seldom used. When they are, they are generally voltage to operate lights, or carry a second telephone line. I wouldn't connect them to anything! Where does it say you should connect black and yellow wires to pins 8 and 2? Your main phoneline is carried on the Red/Green pair. Fm: Cris Agnew 72245,731 If you used to get the Portable magazine get out your Feb 1986 issue and read page 64 - on the schematic you'll see the "B" and "Y" symbol. There is nothing in the article that explains the technical detail about the construction and theory of operation of this device. BTW, thanks for the info on the term of optoisolator, an interesting electronic part - to protect something from high voltage or surge. Fm: Tony Anderson 76703,4062 I can't explain why the publisher of Portable 100, or the editor, who was describing information second-hand, decided to attribute colors to the two wires going to pins 8 and 2. Unless the project had been conceived as a seperate box, in which the circuit was built, and which was connected to the DIN plug with a short piece of standard four-wire telephone "station" wire. It's obvious, to me, anyway, that the author never intended you to connect the device between the red/green and yellow/black wires in the telephone cabling at the wall. Indicating which pin the R, G, Y, and B wires go to in the DIN connector, lends strength to this theory. I would assume that to be the case, as it makes sense to construct the project on perf-board, and mount it in a seperate box outside the computer, and connect it directly into the DIN plug. Another possibility, although I doubt the author thought of it, is to mount the circuit at the wall connection plate, and run the signal connection through the unused yellow and black wires in the standard direct connect modem cable, soldering the yellow and black wires (presently unused) to the appropriate pins in the DIN plug. This would allow you to eliminate the external box, hanging off the DIN plug, for a neater installation... however, you might have problems if you ever used that cable in a system which had voltage or another telephone line on the yellow/black pair at the wall. Fm: Cris Agnew 72245,731 I think it makes more sense if I simply ignore the color-coded wire assignment on the schematic. You may be right about the author intensions. I liked your idea about mounting it on the wall modular ports but I'd need to construct it for portability. Thanks for your help. I'll let you know how it goes. Fm: Tony Anderson 76703,4062 If you can obtain one of the female modular connectors, such as used on the wall connector box or plate, you might consider building the ring-detect circuit in a separate box, which the direct-connect modem cable plugs into, and which then plugs into the wall jack. It would still be portable, but would not be physically attached to the cable, thus allowing you to leave it home, or in your accessory case, when it was not needed. You can probably disassemble one of the cheap Radio Shack modular jack boxes to obtain the jack... or maybe, even build the entire circuit in one of those boxes, with a short modular cable that can be plugged into the wall jack. Would depend on how small you can build the ring detect circuit.