http://www.ti.com/lit/ds/symlink/sn74hc165.pdf
// capture data
digitalWrite(shPin, LOW); // 74HC165 pin 1
digitalWrite(shPin, HIGH);
// read in data
digitalWrite(ssPin, LOW); // 74HC165 pin 15 (but with no Output enable, can be low all the time)
incomingByte = SPI.transfer(0); // shift-in register output connects to arduino's MISO pin
digitalWrite(ssPin, HIGH);