This LED flasher circuit diagram only use two transistors to flashing a led, very simple without IC usage. This circuit will flash a bright LED. The components are not critical and other types of transistors can be use. The flash duration is determined by R2 and C1 and is approximately 3 time constants (3*C1*R2). The LED brightness are controlled by R3 which limit to above 20mA. R1 provides bias for the Q2 for the transistors which should be low enough to not saturate Q2 with the capacitor disconnected. If the circuit not oscillated, it might be R1 to low or R2 to high. D1 allow for high duty cycle operation and limits the reverse voltage at the base of Q1 to -0.7V. D1 may be omitted for low voltage (3-9) and low duty cycle operation.
source : bill bowden’s circuit collection