On Thu, Dec 16, 2010 at 2:54 AM, Justin Richards wrote: >> >> As an example of an alternate approach I sketched this up, 100% untested= : >> >> http://i.imgur.com/dKXND.jpg >> >> Meets requirements except for turn-off delay. =A0 You could slow down >> the circuit with a cap across R2, forming an RC low pass filter, where >> R=3D(R1||R2||R3). >> -- > > I acquired a TL431 from an old PSU and experimented with this example > http://i.imgur.com/dKXND.jpg but could not get it to provide any > hysteresis, i.e the turn on level was the same as the turn off level. > PNP + R3 is meant to provide hysteresis. What is the voltage across R3 when the circuit is off? When it is on? Regards, Mark markrages@gmail --=20 Mark Rages, Engineer Midwest Telecine LLC markrages@midwesttelecine.com --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .