CD4017 Decade Counter IC (DIP-16)

The CD4017 counts clock pulses and lights up one of its ten outputs at a time in sequence, which makes it the chip behind countless classic LED chaser and sequencer projects long before microcontroller-driven animations became the default approach. Beyond decorative lighting, it is also a practical way to divide down a clock signal, step through a fixed sequence of relay-driven stages, or build a basic event sequencer entirely in hardware logic without writing any firmware at all. Its reset input lets a circuit restart the sequence at any output, making it straightforward to build custom-length sequences shorter than its full ten steps by resetting early.