LED Flasher circuit using 2 transistors for LED switching

Below is the LED Flasher circuit using 2 transistors for LED switching. The working principle of this circuit is similar to flip-flop operation.

Component list:

This circuit will flash a bright or high intensity red LED (5000+mcd). Great for fake car alarms or other awareness-raising devices. The component value is not important, try anything else from the trash first. Apparently, the 470 ohm resistor (R3) determines the brightness of the LED and limits the current to around 20mA. The 390 ohm value of R3 can also be implemented as a saved value.

If you decide to use a green or yellow LED that requires extra current, you may want to change the 470ohm to an appropriate value. The flash speed is determined by R2 and C1, which is approximately three time constants (3*R2*C1). R1 provides a bias for Q1 that is low enough not to saturate Q2 when the capacitor is disconnected. When the circuit does not oscillate, it may be that R1 is too low or R2 is too high. D1 allows higher duty cycle operation and limits feedback from the base of Q1 to -0.7 volts. D1 may be omitted for low supply power such as 6-9V and low duty cycle operation.