On 26/06/2008, Jim Lux <[EMAIL PROTECTED]> wrote: >> The key words when working with relays are debouncing, contact >> "wetting" currents and contamination control of contact materials. >> Contrary to the common belief, silver is not the best material for low >> voltage contacts (<24 V) due to the high breakover voltage of the >> naturally developing silver oxide and silver sulphide layers. Gold >> works much better with low voltages and low wetting currents, but is >> suspectible to mechanical wear. Use vacuum protected read relay >> contacts whenever applicable. > > I hadn't ever thought about it before, but devising a rock solid > interface to any sort of contacts that someone might hook up to it is > quite an engineering challenge. Usually, you're designing for some > small subset, or you actually get to pick the contacts. > > I'd guess that you want a fairly decent voltage (12Vish) with a decent > current (10mA), but your input circuit also needs to tolerate > transient voltages, etc. > > Something like an Optoisolator diode with an optional pullup.... > (which is what they use on a lot of industrial PLCs). That would give > you galvanic isolation, too, which is nice. > > Jim > Jim, Optoisolator is a good solution, but even those need some kind of debouncing circuitry, as well as reed relays (sorry for my earlier mispelling: "read relay"!).
Ahti _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
