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Timer circuit is electronic scheme for obtaining signals that last specific time, or have predetermined intervals. If timer circuit generate signal with repetition time intervals it is called astabile mutivibrator. Astabile mutivibrator is also called relaxation oscillator. Point is that this kind of circuit has two stable states that exchange appearance permanently. It is different from harmonic oscillator where output signal is sine like. One way to accomplish astable state is to obtain regenerative feedback with accumulation element (capacitor or inductor) in it, shown in figure bellow.


Regenerative feedback is kind of positive feedback from the output of an amplifier to the input such that the feedback signal is in phase with the input signal. If only one branch in regenerative feedback contain accumulation element, circuit is monostable (Figure bellow).



This kind of circuit must have triggering input that triggers monostable process. Monostable signal is single shoot with predetermined duration.

World most popular integrated circuit for generating astable and monostable signals is NE555 circuit.

In this page following timer schemes are covered:

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