An application for the previous circuit (CB109) is shown here. The central frequency is determined by C and R1. The potentiometer is used to control the range. The minimum value recommended for C1 is 47 pF. Variations in this circuit include the use of a resistive network with a sensor [an LDR for instance]. In this case, the frequency will be dependent on the amount of light in the sensor. Another type of sensor that can be used is an NTC. The frequency in this case, will depend on the temperature. The linear characteristic of the VCO makes it suitable for applications in instrumentation. Digital thermometers or photometers can be designed from this circuit.
Simple Voltage-Controlled Oscillator (VCO) Using the 4046
