74HC165管脚定义： 

使用3个管脚扩展接入个独立开关

const int dataPin = 2;   /* Q7 */

const int clockPin = 3;  /* CP */

const int latchPin = 4;  /* PL */

const int numBits = 8;   /* Set to 8 * number of shift registers */

void setup() {

  Serial.begin(115200);

  pinMode(dataPin, INPUT);

  pinMode(clockPin, OUTPUT);

  pinMode(latchPin, OUTPUT);

}

void loop() {

  // Step 1: Sample

  digitalWrite(latchPin, LOW);

  digitalWrite(latchPin, HIGH);

  // Step 2: Shift

  Serial.print("Bits: ");

  for (int i = 0; i < numBits; i++) {

    int bit = digitalRead(dataPin);

    if (bit == HIGH) {

      Serial.print("1");

    } else {

      Serial.print("0");

    }

    digitalWrite(clockPin, HIGH); // Shift out the next bit

    digitalWrite(clockPin, LOW);

  }

  Serial.println();

  delay(1000);

}