An oscillator that can be frequency controlled by a resistive sensor is shown in the figure. The base is one of the ports of a CMOS 4093 integrated circuit and the frequency depends on both the value of the capacitor used and the resistance of the sensor used. This resistance must be in the range of 10 k ohms to 1 M ohms for better operating stability. The maximum operating frequency of the circuit is around 4 MHz for a supply voltage of 10 volts. An important feature of this circuit is that the signal produced has an active cycle of 50%.
