Flip the switch to turn it on..
This circuit is a 3-stage transistor LED chaser (also known as a 3-phase astable multivibrator or sequential flasher). It is designed to light up groups of LEDs one after the other in a continuous, repeating loop.
The circuit is divided into three identical stages connected in a ring. Each stage contains a Switching Transistor (NPN), which acts a switch. When it turns ON, it connects its group of LEDs to the (0V) ground rail, illuminating them. A Timing Capacitor Controls how long each stage stays turned OFF before passing the signal to the next phase. A Base-Bias Resistor Determines the rate at which the coupled capacitor charges up. Each stage features four parallel-connected group of LED’s (Red, Yellow, and Green) that turn on as a cluster. A Current-Limiting Resistor protects each group of LEDs from excessive current. Power Supply.
How the Sequential Chasing Works: An astable multivibrator has no stable state—it continuously switches back and forth. In a 3-stage version, the stages trigger each other sequentially in a "domino effect"
Stage 1 Active (Red LEDs On): The first NPN transistor is fully ON, driving the column of four red LEDs to glow brightly. Because this transistor is conducting, its collector voltage drops close to (0V).
Stage 2 Inhibited (Yellow LEDs Transitioning): The drop in Stage 1's collector pulls the positive terminal of the middle capacitor down. This forces the base of the second stage's transistor negative, keeping Stage 2 temporarily OFF. As time passes, this capacitor charges through its \90k) resistor. Once the base voltage climbs to about (0.7V) Stage 2 will suddenly snap ON, turning the yellow LEDs on.
Stage 3 Inactive (Green LEDs Off): The third stage is currently resting and unlit while waiting for its preceding trigger phase. Once Stage 2 turns fully ON, it immediately pulls down the next capacitor turning Stage 3 ON and resetting the chain. This loop continuously repeats: Red, Yellow, Green and back to Red..
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