For example, in a power supply for TTL circuits, it can be set to indicate when the voltage is below 4.5 V or above 5.5 V.
Two operational amplifiers with field effect transistors of type CA3140 are used, but equivalents can be tested, including bipolar types such as the 741 or the dual operating MC1458. Just be aware of the operating voltages of the used amplifiers. The two drive values are set in the trimpots which, for greater precision, can be multi-volt type.
The diodes are commonly used and the LED indicator of any color. An amplifier stage may be used to drive a relay or a warning system. The circuit can be used with 5 to 12 V sources.
CI-1, CI-2 - CA3140 or equivalent - operational amplifiers
D1, D2 - 1N4148 - general purpose diodes
LED1 - Common red or other colored LED
Resistors: (1/8 W, 5%)
R1 - 22k ohms
R2 - 1.5 k ohms
P1, P2 - 47 k ohms – trimpots
Several:
Printed circuit board, power supply, wires, solder, etc.
