A very interesting schematic of Flip flop LED flashing circuit. The circuit actually is an astable multivibrator which starts blinking LEDs one by one when power is applied. This LED flasher circuit can be operated with any voltage from 6 to 12 volts, you can also operate the circuit with 3, 4 or 5 volts
only you have to change the values of the current limiting resistors R1 and R4 to 390 ohms.
The flashing rate of the circuit can be increased or decreased by changing the values of R2, R3, C1 and C2. The circuit is using two general purpose BC337 NPN transistors but you can also use other transistors for example 2N2222 and 2N4401 etc.