As shown in the following figure, the Pin 5 terminal of a VCO is the voltage control pin. This pin regulates the trigger to threshold the applied signal levels. Usually, the applied VCC voltage at the supply pin is more as the control voltage will be two-third of the supply pin voltage. The in-built voltage divider causes this division. The pin can also have direct voltage from an external source through a voltage regulating potentiometer. The time for capacitor charging and discharging shall increase with corresponding voltage increase, while the reverse is true in case of decreasing the applied voltage. Hence, the frequency variation is directly reciprocal to the applied voltage, also known as a control voltage. A potentiometer or a transistor circuit output can supply such input control voltage.