Simplest LED Flasher Circuit This may be the simplest LED flasher circuit you can build, with the notable exclusion of LED's with integrated flashing circuits



          



Take a close look. Only the emitter and collector leads of the 2N2222 are connected.
The base lead was cut off.


It was reported that Leona Esaki, who was at Sony at the time, had been surprised to see a negative resistance region while investigating production defects in transistors which lead to his thesis work on the Esaki or Tunnel Diode in 1957, which eventually lead to his receiving the Nobel Prize in 1972.






The 330 uf capacitor is partially discharged through
the transistor, LED, and current limiting resistor


I've tried this with red LED's with and without integrated current limiting resistors, and on some while LED's. This circuit can be built without the current limiting resistor, but if you choose to do so, please be aware that the peak currents may be high enough to shorten the life of the LED.

The capacitor value isn't critical. A lower value will result in faster oscillation and shorter flashes.

The 2N2222 NPN transistor seems to work reliably in this circuit. Other transistors may be more tempermental, and others might not work at all.