Circuit for piezzobuzzer is not that complex. Ground one of the terminal, and apply your pulse train to the other terminal via a driving transistor ( BC548, SL100 or any common transistor ). One terminal ( emitter/collector ) of the transistor to the power supply ( 12V would be better ), one terminal ( collector/emitter ) to the buzzer and give your pulse train to the base of the transistor with some 1K resistor in series. The loudness depends on the ratio of ON time to the OFF time in each cycle.