This bidirectional circuit was found in an American documentation from the 80's. The LEDs are common red, and the resistor is calculated according to the formulas next to the diagram.
This circuit is from National Semiconductor documentation. The operational amplifier is of the...
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...
This circuit, from an American publication of 1974, provides a 0.005% regulation with a variation of...