LM339 Low Power Quad Comparator IC (DIP-14)

A comparator is simpler than an op-amp in purpose but just as fundamental: rather than amplifying a signal, it only decides which of two input voltages is higher and snaps its output fully high or low based on the answer. The LM339 packs four of these comparators into one chip, which is handy for building multiple independent threshold-detection circuits at once, such as battery low-voltage warnings, multi-level light or sound threshold indicators, or simple analog-to-digital trigger stages that fire once a sensor crosses a set level. Its low power draw and single-supply operation make it practical for always-on monitoring circuits that need to stay alert without consuming much current themselves.