Russell that is pretty clever, I am half tempted to give it a try on one of my existing prototype boards just to see if it works. The next revision will probably get Schmitt trigger ICs since this is (will be) a safety sensitive application. On Thursday, August 29, 2019, RussellMc wrote: > On Fri, 30 Aug 2019 at 09:05, Jason White < > whitewaterssoftwareinfo@gmail.com> > wrote: > > > My application is space and power constrained. Is there a logic gate th= at > > does not exhibit this behavior? (100uA in the undefined would be much mor= e > acceptable than 45mA) Maybe a schmitt trigger would be designed to > > > > > > A Schmitt triggered gate is the obvious solution, as you and others hav= e > noted. > Below I describe an extremely 'naughty' concept which may be able to be > made to work deep-ending on overall situation. > This arrangement > > - may not work at all > - may be an utter disaster > - may be able to be made to work extremely well > > Odds are the naughtiness factor exceeds the levels acceptable in a real > world design :-). > > "" Solution """: Add a 'suitably sized' resistor in the IC's Vdd line. > > Greatly increased current drain will lower the IC's Vdd thus increasing t= he > relative voltage of the inputs relative to the IC. > Reduction of current drain will restore the voltages so there is a > potential for oscillation depending on time constants. > > (This "works", if at all, on rising input waveforms. > A resistor in the Vss line will achieve a similar result with falling > inputs. > Both at once (probably) don't work for equal sized resistors. Assymetric > sizing may work in both directions in some cases but, by then magic is > probably safer). > > I have never tried this with an IC. > But I have successfully added hysteresis in a transistor based circuit by > adding a small resistor in a current path and using the small pedestal to > raise a switching voltage level elsewhere. Not a formal Schmitt per se. I= n > that case the solution was 'almost elegant' rather than 'naughty' and > produced superb results with astonishingly small levels of hysteresis for > the results achieved. (ie calculation suggested that the level that worke= d > was far smaller than would be expected to be effective. > > > Russell > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Jason White --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .