Two-LED Alternating Flasher

Circuit Diagram

How to Build It

1. Place the two NPN transistors (2N3904) on the breadboard, a few centimeters apart.
2. Connect each transistor's emitter to the negative rail (GND).
3. Connect transistor 1's collector through a 1K resistor to the positive rail, then connect LED 1 in parallel with that resistor (anode toward +).
4. Repeat identically for transistor 2 with LED 2.
5. Connect a 100uF capacitor from transistor 1's collector to transistor 2's base.
6. Connect a second 100uF capacitor from transistor 2's collector to transistor 1's base.
7. Connect each transistor's base through a 4.7K resistor to the positive rail.
8. Power with 9V — the LEDs should blink alternately, one after the other.

Bill of Materials