Capacitive Humidity Sensor to Analog Output Converter

The project presented here is an analog capacitive humidity sensor converter board suitable for various humidity measurement tasks. The circuit comes from Texas Instruments application note (see below). Most conventional capacitive proximity sensors produce a digital signal, but this circuit produces a DC output voltage that is a function of the relative humidity of the environment. The oscillator input for this circuit is a 1Khz sine source (1V_pp) feed to FQ input. The low frequency and sine characteristics keep RFI problems at a minimum. This sensor output converter may prove difficult to construct because of the small capacitances involved, parasitic capacitances in the sensor circuit, and noise pickup. The circuit requires an external 1Khz sinewave with 1V_pp signal and operates with a dual 15V DC supply.