Schematic Circuit Diagram Voltage Controlled Oscillator (VCO) proteus simulation

VCO Using 555-Timer

The Control Voltage terminal of the IC is internally preset at 2/3 Vcc. When the timer is operating in astable mode, if this voltage is altered externally through a potentiometer, the pre-set voltage levels with which the comparators compare the voltage at capacitor will change. This causes the shifting of Set and Reset instants of the timer. As the control voltage increases, the time period of oscillation increases and vice versa.