This is Automatic duty control circuit. We can use the Schmitt trigger to generate the simple square wave. The duty factor of the output waveform will be determined by the input waveform. But the threshold level is the importance.

In Figure 1 will have the output while input waveform as Figure 2 cannot have output.

Figure 2 the waveform of this circuit

How Automatic duty control works

The small input signal is connected to circuit through the capacitors C1. The level of output is the average by R2 / C2 and feedback to input.
The adjustment the DC voltage at input to control the peak voltage of the input signal.

When the input signal is fed into a large excess of the threshold level of schmitt trigger both positive and negative side. It will be a square wave at the output. The sensitivity of the tuned circuit at P1.

The disadvantage of this circuit is that. If no the input signal. The circuit is working as a frequency generator. To prevent this problem, We must have a frequency at least 10 times. (The circuit is 100 Hz,)

Using this circuit may be used as a trigger to automatically oscillator’s frequency spectrum.

Another disadvantage of the circuit. If the input signal is very small duty factor at the top of the sign. Pulse output quality is not good.

Parts you will need
IC1____CD40106_______CMOS Hex Schmitt Triggers
R1_____1M_______1/4W Resistors tolerance: 5%
R2_____100K_____1/4W Resistors tolerance: 5%
C1_____100nF or 0.1uF 50V___Polyester Capacitor
P1______1M Pot