Jinx wrote: >> By Schmitt trigger do you mean one that was built using an op-amp >> and not an IC? I got stuck because I was looking at Schmitt-Trigger >> IC datasheets (like a monkey with a math puzzle) and all I could see >> was A1 in and Y1 out and no way so adjust the trigger value. Is this >> correct? > > You can make an ST, eg with a couple of transistors, that has a movable > trigger voltage. ST ICs (4093, 74xx14, PIC i/ps etc) are made with fixed > thresholds. A comparator or op-amp with high gain should be OK as an > ST in an analogue application I meant a ST made with an op amp and positive feedback. National has a few app notes with 100s of op amp circuits, and you find them in there. These have the advantage over logic ST inputs that you can control both the threshold and the hysteresis. This is desirable in most analog applications. And by selecting the op amp (and the circuit and the other components) properly, you can also control the precision of threshold and hysteresis -- again something that isn't really possible with digital ST inputs. Vcc | | R1 input signal---- inv in opamp | opamp out--+--- ST output +--------------------- noninv in opamp | | | | | +-------------------------R2-----------------+ | R3 | Gnd That's the basic opamp ST circuit. R1 and R3 determine the threshold, and R2 (together with R1 and R3) determine the hysteresis. Gerhard -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist