Mainly composed of clock generation circuit and decimal counter circuit. The self-excited multivibrator uses NE555 as the core. The power supply charges capacitor C1 through R2, R3, and R4. When C1 starts charging, the 2nd pin of NE555 is at low level, so the output pin 3 is high. When the voltage across C1 reaches 2/3 of the supply voltage through R2, R3, and R4, the output pin 3 changes from high to low, turning on the internal discharge transistor of NE555. Capacitor C1 discharges through pins 7, R4, and R3 until the voltage across C1 drops below 1/3 of the supply voltage. Then, the 3rd pin of NE555 changes from low to high, and C1 begins charging again, creating a continuous oscillation cycle. The charging time is 0.695 × (R2 + R3 + R4) × C1. The discharge time is 0.695 × (R4 + R3) × C1. Adjusting R4 controls the oscillator's output frequency. The clock signal from NE555 is continuously applied to the 14th pin of CD4017. Ten LEDs are connected to the 10 outputs of CD4017. As the CD4017 outputs sequentially go high in response to the clock signal, LEDs D1 through D10 light up one after another, creating a flowing water-light effect. Adjust R4 to control the speed of the LED sequence. 2 x Module Item Type: Flowing Water Light Voltage: 2.5–14.5V Size: 5.4 x 2.1cm / 2.13 x 0.83in Thickness: 1.6mm