The Voltage Controlled Oscillator (VCO for short), is a very practical circuit for generating square and sine waves. While these waves can be produced using the Simple Function Generator Kit, the VCO allows for controlling the output frequency with the use of a voltage signal instead of using a potentiometer. This means that the output frequency of the VCO can easily be controlled by microcontrollers and other analogue circuits which can create some pretty interesting results. For example, a 1V octave synthesiser can be built using this module whereby a 1V octave keyboard is connected to an exponential converter which feeds its output into the VCO to produce keyboard tones. This circuit can also be used in retro ways such as sensor data transmission where the voltage output of a sensor is converted into a frequency and the frequency of the output will be proportional to the sensor reading (a similar system was done in early satellites such as Sputnik).