Acceptable Voltage Indicator
I have used this circuit many times in custom test fixtures where a simple go-no go
indication was needed. The circuit can also be used to adjust a particular voltage
be within specific high or low limits. The three LEDs will indicate if the voltage
is high, low or OK. When connected to other converters, such as a frequency to
voltage converter, a current to voltage converter or a power to voltage meter, it could
provide a quick indication of a proper level.