The 74HC595 is a 16-pin (DIP-16) shift register IC that lets a microcontroller control 8 separate outputs using only 3 digital pins. It receives data bit by bit on the DS pin, shifts it in with SH_CP clock pulses and copies it to all eight outputs (Q0–Q7) at once with a pulse on ST_CP (latch). Running on 2–6 V, it works with Arduino, ESP32 and Raspberry Pi Pico. Connecting the Q7' output to the DS input of the next chip builds a chain, so the same 3 pins can drive 16, 24 or more outputs. In a typical setup, DS, SH_CP and ST_CP go to three digital pins, OE to GND and MR to VCC; every LED needs its own resistor (220–330 Ω), and relays or motors need a transistor. On Arduino it is driven with shiftOut(). It is used to add outputs in chasing LED, 7-segment display, LED bar graph, LED cube and multi-channel relay projects.