trigger with presettable thresholds

7-42 elektor july/august 1980 56 Most triggers with switch hysteresis (the schmitt-trigger included) have switching thresholds which cannot easily be preset (if at all) because the levels affect each other or the switching behaviour of the trigger. This particular trigger is an exception and consists of three opamps. The switching thresholds can be preset between 0 and 83% of the positive as well as the negative supply voltage, independently of each other, by means of Pl and P2. It makes no difference which pot is used as the upper or lower threshold. Only when the input voltage is higher than the highest preset threshold voltage, will outputs A1 and A2 both be "low". The voltage on pin 10 of A3 will then be lower than that on pin 9, causing the output voltage to be- come negative. The trigger can operate with DC or AC signals. The peak values of the input signal must of course remain within the supply voltage"s limits. trigger with presettable thresholds A1,A2,A3 = 3/4 TL 084 805...