Classic LED Flasher Circuit

This LED flasher circuit is a classic two transistor flip flop. This flasher circuit is very popular and it’s usually the first circuit to build when starting electronic circuit building hobby. Here is the schematic diagram of the famous LED flasher circuit:

How LED Flasher Circuit Works

The circuit consist of two transistors, two capacitors, four resistors, and two LEDs.  When the power supply is first connected to this LED flasher circuit, both transistor is racing to be triggered first by the base current through 100k resistor. Actually when one transistor is triggered first than the other, the first activated transistor will behave like a closed switch, so the LED will turn ON and the base of the other transistor will be grounded through the capacitor. This grounding keep the first transistor to be activated and the second one to stay off untill the capacitor is charged above the bias voltage needed to activate the second transistor. After reaching this voltage, the second transistor will be switched on and now the second transistor will turn ON the LED on its collector, turning off the first transistor by grounding its base through the second capacitor. This alternating process will be repeated forever until the power supply is turned off. The flashing rate will depend on the resistors (100k) and the capacitors values. You can change the values of the capacitors to change the flashing frequency. Use a higher capacitance value for lower flashing rate, and vice verse.