Calibration-less direct capacitor-to-microcontroller interface

• Published in: Electronics letters Vol. 52; no. 4; pp. 289 - 291
• Main Authors: Lopez-Lapeña, O, Serrano-Finetti, E, Casas, O
• Format: Journal Article Publication
• Language: English
• Published: The Institution of Engineering and Technology 18.02.2016; Institution of Electrical Engineers
• Subjects: Calibration; calibrationless direct capacitor-to-microcontroller interface; capacitance 33 nF to 4.7 nF; capacitance 33 nF to 4.7 nF; capacitance measurement; capacitive sensor; capacitive sensors; capacitor charge; capacitor discharge; capacitor measurement; Capacitors; Charge; Circuits; cost reduction; Detectors; Deviation; direct sensor-to-microcontroller interface circuit; electron device testing; Electronics; Enginyeria electrònica; Instrumentation and measurement; Mathematical analysis; measurement process; Microcontroladors; Microcontrollers; nonlinear equation; nonlinear equations; reference value; Sensors; space reduction; temperature 18 degC to 70 degC; Àrees temàtiques de la UPC; cost reduction; capacitor charge; capacitive sensors; space reduction; nonlinear equations; capacitive sensor; capacitors; capacitance 33 nF to 4.7 nF; direct sensor-to-microcontroller interface circuit; measurement process; reference value; capacitor measurement; electron device testing; calibrationless direct capacitor-to-microcontroller interface; capacitor discharge; temperature 18 degC to 70 degC; capacitance measurement; nonlinear equation; microcontrollers
• ISSN: 0013-5194; 1350-911X; 1350-911X
• DOI: 10.1049/el.2015.3706

A new technique to measure a capacitor or a capacitive sensor by means of a direct sensor-to-microcontroller interface circuit that does not need a calibration capacitor is proposed. Basically, the measurement process consists of three consecutive steps of charge, discharge and charge of the capacitor under test. A non-linear equation is obtained and solved that is dependent only on known circuit parameters. Experimental results show that it is possible to measure a wide range of capacitor values with a maximum deviation of 2% from the reference value, and that temperature changes from 18 to 70°C yield relative errors below 0.1%. For the lowest measured capacitor range (33 pF–4.7 nF) the uncertainty holds below 1 pF which enables measurement of commercially available capacitive sensors. The main advantage of the proposed technique is cost and space reduction of the final design.