A requirement in many applications is a spontaneous source of a series of continuous signal with a regular and definable waveform. One of the most important of these is a square wave. The circuit on the right will control a comparator with positive and negative feedback to the output voltage. Since the negative feedback path uses a capacitor, while the positive feedback path, but there is a time change from the comparator triggered her condition. As a result, the circuit oscillates, or changes the status back and forth on a predictable price. Square Wave Generator (100Hz) circuit Three-phase 100Hz frequencies with 9V battery count, minimal parts This simple circuit is a good and stable 1V peak to peak square wave at 100Hz, 1kHz and 10kHz with a single cell 1.5V power supply. A useful feature of this circuit is that frequency changes can be achieved only by switching on a capacitor at a time. The power consumption is about 600μA.