The simplest is the use of transistors or often called a flip-flop. There also are using integrated circuit such as IC 555. There's more to exploit the resonance of the capacitor and inductor relationship as oscillators. To be sure whatever form and whatever the circuit components used must be able to generate electric waves which have a peak voltage (logic 1) and valleys (logic 0) is continuous.
Any variation of pulse generator circuit design has advantages and disadvantages of each, just how your decision for the appropriate circuit. For example to create a clock signal for a simple utility that you can only take advantage of the transistor but if you need a more accurate clock signal and form a perfect balance you can use IC Astable or logic gates. Or perhaps you need a signal with very high frequency (up to MHz) you can use a combination of inductor, resistor and capacitor.
Frequency value of the pulse generator circuit gate above is determined by the value kapaitor C2, R2, R3 and VR2. The greater the value of these components will lower the frequency and vice versa. Actually nothing is difficult to make a series of pulse generators, almost all time-based series is utilizing the nature of the charge and discharge capacitor. Therefore, like any form of variations in pulse generator circuit, always have a larger capacitor value will make the frequency produced smaller or longer periods of time, sedangkaan smaller capacitor values will result in greater output frequency.