Minimum parts counting
Designed for 3V battery operation
R1_______33K 1/4W Resistor R2,R3____47R 1/4W Resistors C1_______10µF 25V Electrolytic Capacitor D1,(D2)__LED(s) (Any type and color) Q1_____BC560 45V 100mA PNP Transistor Q2_____BC337 45V 800mA NPN Transistor
Power supply can vary from 2 to 4.5V.
Add D2 to obtain two LED alternate blinking.
D1's on-time is shorter than off-time. The opposite regarding D2.
You can also use D2 only, shorting D1.
Don't change resistors' values.
Flashing frequency can be varied changing C1 value from 2.2µF to 100µF and higher.
This circuit is very efficient when driving a 3.2V lamp. In this case omit the LEDs and R3, connecting the lamp at Q2's collector and to positive supply, further reducing parts counting.