Post by thread:Opto Couplers etc.

This is for anyone contemplating using opto couplers or similar devices in projects. "USE ONLY AS A LAST RESORT!" Why? They are SLOOOOOOOOOOW! So before you design them into a project, go to SIEMENS web site <http://www.siemens.com>, find the opto app notes section and get app notes 1, 2, 4 and 5 as a minimum. They are in .PDF format and although small, ther is enough info there to put you on the right track. Good luck with your projects, Bill

In a message dated 98-01-16 20:24:07 EST, you write: << This is for anyone contemplating using opto couplers or similar devices in projects. "USE ONLY AS A LAST RESORT!" Why? They are SLOOOOOOOOOOW! So before you design them into a project, go to SIEMENS web site <http://www.siemens.com>, find the opto app notes section and get app notes 1, 2, 4 and 5 as a minimum. They are in .PDF format and although small, ther is enough info there to put you on the right track. Good luck with your projects, Bill >> They're not all so slow. The NEC PS9601 has a propagation delay of 50ns. You can commonly find them in the 1-8 microsecond range. Dave Duley

>This is for anyone contemplating using opto couplers or similar devices in >projects. > > "USE ONLY AS A LAST RESORT!" > >Why? They are SLOOOOOOOOOOW! > Not necesarily, maybe most commercial ones are, but there are also very (extremely) fats optical sensors and transmitters. Just imagine the speeds of fiber optics comms. Gabriel TGO Electronica Mexico ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com

> maybe most commercial ones are, but there are also very (extremely) fats > optical sensors and transmitters. Just imagine the speeds of fiber > optics comms. In project at work, I frequently run about 50kbsp synchronous through the (reasonably-priced) optoes we use. Pushing things to 250kpbs works just fine with these optoes, but since the application gets no further benefit, I prefer to keep the safety margin I get with the slower speeds (at the faster speeds the signals look pretty mungey). I don't know off-hand what type of optoes we're using, but this is with what the parts- selection guy regards as relatively "vanilla" optoes; the slightly more expensive optoes can operate at 500kps with decent-looking waveforms.

I feel that this is an over-simplification. HP and others have optos that have bandwidths as high as 10 Mbits/sec. Perhaps in your application this is SLOOOOOOW. It's true that if you pick up an opto that is constructed with an led and photo-transistor (or worse, a photodarlington), it will be sloooow. As soon as you substitute an opto that is constructed with a PIN diode and transistor instead of a phototransistor, the bandwidth goes up to about 1Mbit/sec. So you pick your performance and pay the price.... Regards, Jim Ham At 08:23 PM 1/16/98 -0500, you wrote: {Quote hidden}>This is for anyone contemplating using opto couplers or similar devices in >projects. > > "USE ONLY AS A LAST RESORT!" > >Why? They are SLOOOOOOOOOOW! > >So before you design them into a project, go to SIEMENS web site ><http://www.siemens.com>, find the opto app notes section and get app notes >1, 2, 4 and 5 as a minimum. They are in .PDF format and although small, >ther is enough info there to put you on the right track. > >Good luck with your projects, >Bill > > Jim Ham, Porcine Associates (415)326-2669 fax(415)326-1071 "http://www.porcine.com"

Ladies & gentlemen, I'd like to make a couple of points for clarification: 1. My comments were to those of us who don't have big budgets and clients to pay for our fun and games. It is intended for those who have to buy (at least on occasions) over the counter at the local Tandy or DSE. I don't think I am the only one in that boat. 2. Lazer & fiber optics comms have less in common with opto couplers than does chalk with cheese. They aren't in the same league by any stretch of the imagination. It is easy to assume that because optical comms is fast, all optical connections are fast. This is not so and probably to a greater extent than most realise. The app notes I mentioned provided me with the only explanation of device characteristics I have been able to find. Text books and most (all) data sheets are useless and down right misleading. Bill

> In project at work, I frequently run about 50kbsp synchronous through > the (reasonably-priced) optoes we use. The vanilla opto's seem to get a bit of a rough deal through misapplication. The trick is to remember that it is a transistor and treat it the same as you would any other transistor that you want to get good speed out of. Keep the collector current as low as needed. Putting a resistor (100k) from base to ground gives a cheap and dramatic speed improvement. Steve. ====================================================== Very funny Scotty. Now beam down my clothes. ====================================================== Steve Baldwin Electronic Product Design TLA Microsystems Ltd Microcontroller Specialists PO Box 15-680 email: spam_OUTstevebTakeThisOuTkcbbs.gen.nz New Lynn, Auckland ph +64 9 820-2221 New Zealand fax +64 9 820-1929 ======================================================