This circuit generates a square-wave which is useful as a clock signal or AC drive for the excitation of sensors. this article presents a square-wave oscillator. This circuit requires no external components unless the bypass capacitor. Figure below shows the circuit, the output frequency and a scope shot of the output waveform.
AC-powered subsystems or a square-wave (clock) generator for driving digital is required by systems. Some sensors also require the use of an AC drive. Electro-chemical sensors (e.g., for monitoring conductivity, moisture,and tilt) cannot tolerate DC current, because it degrades the materials of which they are made. For example piezoresistive sensors, an AC drive cancels DC errors and low-frequency noise.
This circuit produces a powerful 3V to 5V square-wave output with very low source impedance (less than 10ohm). Not only produces a powerful square wave, but also provides rail-to-rail excursions in a small SOT23 package. The output frequency is reasonably stable with variations in supply voltage and temperature.
The circuit has a dependable start response, even with supply voltages below 1V (depending on the MAX1697 version used). This circuit is very simple, so it is a lack of flexibility in output frequency.