This window generator uses a single LM324 op amp and features two adjustable set points. When the two comparators formed b
y U1B go high, LED1 lights. When U1C goes high, the LED extinguishes. Some hysteresis is provided by the 10-mi2 resistors. As shown in Fig. 104-2(b), LED1 can be replaced by an optoisolator (etc.) for use in several applications.