Minimum parts counting

Designed for 3V battery operation

Parts:

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

Notes:

• 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.