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.
We found this circuit in the October 1992 Radio Electronics magazine. The frequency is given by C1...
This conventional LED flasher circuit has a configurable multivibrator configuration with PNP...
This extremely slow circuit produces one pulse per month and can be used in a timer. We found it...