Built an LED Chaser Circuit with 555 Timer IC and CD4017

The LED chaser circuit operates by combining an astable multivibrator stage with a digital decade counter stage, all powered by a 9V battery. The heart of the timing section is the NE555 Timer IC, configured alongside a 50K ohm potentiometer, a 1K ohm resistor, a 10uF electrolytic capacitor, and a 0.1uF ceramic capacitor. In this astable configuration, the 555 timer continuously charges and discharges the capacitors through the resistive network, generating a steady train of clock pulses at its output pin. The frequency of these pulses—and therefore the speed of the chaser effect—can be dynamically adjusted by turning the 50K variable resistor. These clock pulses are fed directly into the clock input of the CD4017 Decade Counter IC. Upon receiving each rising edge of the clock signal, the CD4017 advances its internal state, sequentially activating its ten decoded output pins one by one in a repeating loop from zero to nine. Each of the ten outputs is connected to a blue LED paired with an individual 220 ohm current-limiting resistor to ensure safe operating currents. As the CD4017 cycles through its outputs, the blue LEDs illuminate one after another in a linear sequence, producing the classic running-light effect. Because the circuit is built on a breadboard using jumper wires without a dedicated printed circuit board, the entire system relies on proper analog and digital pin connections to maintain signal integrity between the timing generation and sequential logic stages.