A Novel Oscillator Based Signal Conditioning Circuit for Online Measurement of Capacitive Sensors

A novel and simple oscillator based interface circuit for the medium range capacitive sensor (1μF to 100μF) is presented. Op-amp based Hartley oscillator circuit is used to convert a change in capacitance to change in frequency. As the output of the signal conditioning circuit is frequency, so it is very easy to use this frequency directly for transmission in communication systems. In this manner, the presented circuit can be used directly for acquiring the reading from the remotely placed sensors. An IoT based circuit system is also presented here for online measuring the capacitance and display it on the local server. The described circuit is simple to build and as it is op-amp based circuit, so losses are very less and there is negligible loading effect while connected to the sensor. The output frequency from the oscillator circuit is measured, and then it is converted into an equivalent voltage, which then measured by Arduino and Raspberry-pi sends this measured values to the Wi-Fi based server for online display.