A New Approach to Capacitive Sensor Measurements Based on a Microcontroller and a Three-Gate Stable RC Oscillator

A complete smart capacitive sensor solution based on a microcontroller was developed. This approach includes the development of both the hardware and software. The hardware part comprises an 8-bit microcontroller equipped with two timers/counters and a three-gate stable RC relaxation oscillator. The software part handles system configuration, measurement control, communication control, and data processing. Hence, the microcontroller acts as a frequency meter with an adaptive measuring time, and the relaxation oscillator generates a square wave with a frequency depending on the value of the capacitance of the sensor. The article also proposes a calibration method that reduces the measurement range to 1 pF. The experimentally proven relative measurement errors of sensor capacitance are less than 0.012% for values smaller than 12 pF, and less than 0.0084% for values from 12 to 300 pF.