This is a simple pulse generator circuit or standard astable oscillator circuit for IC 555 timer,NE555N IC.
Use for digital Logic circuit. IC 555 use voltage supply 5V to 15V.
the output frequency will be approximately 1kHz and the duty cycle 50-50, The output’s frequency is control by R1.
The values in the formula are expressed in ohms, farads, seconds and hertz. This formula is much simpler than that of the previous circuit.
Detail more, Please read in this image circuit.