optical voltage indicator

optical voltage indicator This circuit indicates, by means of a flashing LED, when a voltage being monitored or measured falls below a predetermined value. The only active component is an op-amp which functions as comparator and as oscillator. The voltage to be monitored is applied to terminal A and the refer- ence voltage to terminal B. As long as the voltage at the non-inverting input of the op-amp is larger than 12V that at the inverting input, the output of the op-amp is 12 V and the LED does not light. If the voltage at terminal A, and there- fore U+, drops below the reference voltage, U-, the op-amp inverts and the LED lights. A feedback loop, R2/R 1, causes U+ to be reduced somewhat. Capacitor Cl charges via R3 and the output of the op-amp. Diode Dl cuts off, so that the voltage at terminal B no longer affects U. When U - has dropped 2 12V 12V D~2R 1N4148 1N4148 C,I 1V~ R3 16V 220k 84 fff D3 2- G IC1 D+ 741 n+ 6 83596 1 BA R 83596 2 till it is just below the level of U+, th...