Everyone eventually runs into the problem of running out of I/O pins on the Arduino, and the Raspberry Pi. A shift register is a chip that can give you 8 or more additional I/O ports, while only using 3 ports on the microcontroller. There are input and output shift registers, and today I’m showing an example of an output shift register,the 74HC595.
I’ve taken an Adafruit protoboard, and soldered in a 74HC595, 8 LED’s, and 8 220 ohm resistors.
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The tutorial I followed is found at https://www.arduino.cc/en/Tutorial/ShiftOut and documents the construction,and gives three example sketches.