We propose to build at a cost insignificant (a few euros) an oscillator using the integrated timer 555. This proposal is a kind of relaxation oscillator for generating output square wave of fixed frequency up to 500kHz with the possibility of different Duty Cycle between 50 -100%. Unlike 's use of the 555 timer in a monostable circuit which produces a single pulse output (one-shot), when activated on its input pin 2 (trigger), in order to obtain the oscillator from 555 to astable Multivibrator , you must continuously re-activate the IC 555, after each cycle timing..