Gerhard Fiedler wrote: > > At 09:16 03/13/99 -0800, Mark Willis wrote: > > But RS485 type stuff makes sense (One box I did could use leased-line > >modems, RS-422, RS-232, RS-485, or fiber > > what makes the 485 protocols special (as compared to 232 or 422) is that > you have exactly the same half duplex situation you have with one fiber. > > >Main thing I'm curious about > >is how LED to LED opto comms would work > > that's interesting. could you please post your results? :0 > > ge RS-485: I usually go half duplex anyways, habit I guess I try to keep control traffic to a minimum, and use smart peripherals. Sure will share results; I'll probably be begging for help here, as Analog is sort of a weak area for me (Haven't been doing it enough, have lost SO much of it...) IIRC there was a bookmark here somewhere, lessee: Nope, cannot find it. Some electronics mag had an article about "This LED makes the best red laser light receptor" or some such. IIRC all such results are dependent on the similarity of the particular LED's you use, too (I'd think SMD LED's with the light pipe right on them, would work about the best?) And you want as close to identical LED's as you can get, for best voltage response. Grabbed a 10mm Radio Shack "12000 mCd" Ultrabright Orange LED that's sitting at hand here (Was showing someone how dang bright those are!) - I get about 0.002V when dark, and about 0.016V across it from the light coming in the skylight in the nice tall ceiling here (Sorta a grey cloudy day.) Hardly an ideal color match, huh? Putting it 2" or so from a lit taper candle here gives me a nice varying 0.7 - 0.9 V. I'll have to go grab a pair of red identical LED's - I suspect I'll want some amplification in here, unless I use better LED's - or a PIC that has an ADC built in It'd sure be nice to end up with a design that only uses one PIC pin, too... Easy enough to amplify .7V to 5V with one transistor, but doing that with 1 PIC pin on the central PIC is something I'll have to think about. Maybe one common collector supply and 1 pin for all 10 transceivers, off a 16F84, say, to switch modes? (i.e. RA4 pulls low, causes the +V supply on the transistor amplifiers to activate, etc.) I'll play with it, not in a rush yet but want it eventually to be a "Known good or bad" idea Mark