You can build this simple PWM controlled pulse generator circuit with the help of a single inverter gate, which may be in the form of a single gate from the IC 4093 with its input pins shorted together, or simply a NOT gate.
How the Circuit Works
Any one of the total four gates can be used to produce an oscillator with a variable duty-cycle and a set frequency. The RC time-constant of this network that has a capacitor C1 and resistor R1+P1 helps in determining the pulse duration.
A perfectly symmetrical square wave signal is obtained at output when the wiper of this potentiometer is adjusted in the mid-position. In any case, when the position of the P1 is altered, the C1 takes a different time to discharge.
Due to this, sooner or later, gate N1 gets triggered and results in either positive or negative-going. This concludes to the fact that the pulse width varies.
R1 acts as a protective measure in case the P1 is at minimum resistance. This means that the duty-cycle is not 100% variable but a 98% range is perfectly acceptable.
Variable Oscillator Pulse
The value of the capacitor C1 also determines the frequency of the oscillator as the sum of RC-time constant is the same for both. Often times, several different frequencies are required, a multi-way switch with a corresponding number of capacitors can be included to replace C1 (refer figure below). This lets the pulse duration to be different in corresponding steps from the switch.
is the circuit capable of producing a 1Hz signal?
yes it is capable.