Arduino Shift Register Input. Then connect pin 8 gnd and pin 13 oe to the gnd pin of the arduino. This means you can read the state of up to 8 digital inputs attached to the register all at once.
Sometimes you ll end up needing more digital input than there are pins on your arduino. Shift registers come in two main types a sipo serial in parallel out or piso parallel in serial out. By using a simple shift register like the cd4021 you can add up to 8 additional inputs using only 3 pins on your arduino.
First you need to set the serial input of the register digital pin 2 on the arduino high or low next you need to flip the clock pin digital pin 3 from low to high the shift register will read the data on the serial input and shift the output pins by 1 repeat 8 times and you have set all 8 outputs.
If you use an esp8266 board i use the digital pins d0 d1 and d2 for the storage register and shift register clock input as well was the serial data input. They are cheap. This means you can read the state of up to 8 digital inputs attached to the register all at once. Since you already have input use an 74hc165 8 bit parallel in serial out shift register.
