A serial in/serial out shift register transfers data from one line of a parallel bus to another line one bit at a time.

Most sequential circuits contain a combinational logic section and a memory section.

Phototransistors have varying resistance from collector to emitter, depending on how much light strikes them.

Counters are generally decoded in order to determine their count state.

The term synchronous, as applied to counter operations, means that the counter is clocked such that each flip-flop in the counter is triggered at the same time.