Measurement Of Capacitance Using Arduino Lab Report

Measurement of Capacitance using Arduino – An Interrupt-based Approach: Part I

SAIKAT PATRA, SHIBENDU MAHATA

Introduction

Capacitive sensors are widely employed to measure various physical and chemical process parameters such as displacement, acceleration, thickness, force, pressure, stress, level, and humidity. The measured value of capacitance is then calibrated in terms of the process parameter for indication and/or control applications. This project presents an interrupt-based approach by employing a 555 timer operating in astable multivibrator mode and an Arduino Uno to continuously measure capacitance in the range of 1 µF - 1 mF and provide local indication using a liquid crystal display (LCD) and data acquisition using personal computer
The timer is powered with +5V from the Arduino board, thus eliminating the need for an external dc power supply. The timer generates a square-wave output of amplitude +5V at a specific frequency (depending on the values of R1, R2 and Cx) through pin no. 3. The output of the timer is connected to pin no. 2 of the Arduino. Since this pin of the Arduino is a hardware interrupt pin (called Interrupt 0), the source code (“capacitance.ino”) uploaded to the Arduino uses an interrupt-handler which is executed whenever the timer output makes a LOW-to-HIGH transition. Thus, the time-period of the square wave is continuously obtained by calculating the time difference between two such consecutive transitions. The time-period (T) of oscillation for the square-wave output from the 555 timer is given
4: 555 timer connection in our breakout board

Arduino Uno Board: Arduino Uno is an AVR ATmega328P microcontroller based development board with 6 analog input pins and 14 digital I/O pins. The microcontroller has 32 KB of ISP flash memory, 2 KB RAM and 1 KB EEPROM. The board provides capability of serial communication via UART, SPI and I2C. The microcontroller can operate at a clock frequency of 16 MHz. In our project, the digital I/O pins 3, 4, 5, 6, 11, and 12 of the Arduino are connected with pin nos. 14, 13, 12, 11, 6, and 4, respectively, of the LCD.

16×2 character LCD: Since our Arduino program (“capacitance.ino”) uses the LCD in 4-bit mode, only the LCD data lines D3-D7 are configured for reading data from Arduino. Pin nos. 1 and 2 of the LCD are connected to GND and 5V, respectively, from the Arduino board. The Read/Write pin (pin no. 5) of the LCD is connected to GND. A 10 KΩ potentiometer is provided for adjusting the contrast of the display.

The entire list of components used for this project is shown in Table I.

Table I. Parts list

Name
No. of