555 Timer

Inside the 555 are two comparators (at ⅓ and ⅔ of $V_{CC}$), an SR flip-flop, a discharge transistor and an output stage. It runs from 4.5–16 V (CMOS versions like the TLC555 from 2 V).

Pins: 1 GND, 2 Trigger, 3 Output, 4 Reset, 5 Control, 6 Threshold, 7 Discharge, 8 $V_{CC}$.