PIC Microcontroller Based Portable Spectroscopy Sensor for Liquids: A Novel Approach

Transcription

1 PIC Microcontroller Based Portable Spectroscopy Sensor for Liquids: A Novel Approach S. M. Anpat #1, S. B. Sayyad *2, P. W. Khirade **3 #Dept. of Electronics, Vidya Prathisthan`s ASC College, Baramati (MH), India *Dept. of Physics, Milliya College, Beed, (MH), India **Dept. of Physics, Dr. BAMU Aurangabad, (MH), India 1sandipanpat2@gmail.com, 2 syedsb@rediffmail.com, 3 pwkhirade59@gmail.com Abstract The present paper introduced a PIC16F628 microcontroller based portable spectroscopy sensor for measurement of dielectric constant of liquids. The developed sensor system is based on the principle of frequency variation by dielectric medium. It is based on the measurement of the frequency, as a function of permittivity of a liquid medium. A liquid holder, cell is fabricated, in which liquid is inserted as a dielectric medium and this liquid holder cell further connected to XR2206 function generator. The frequency of function generator varies according to the permittivity of the medium inserted into liquid holder cell. The PIC16F628 Microcontroller is employed for the measurement and display the frequency. The implemented sensor system is successfully sense broad range of dielectric constant of liquids with an accuracy of ± 0.1 percent. The liquid sample required is about 0.3 ml. The present sensor system is compact, portable and cost effective. Keywords Permittivity, PIC16F628 Microcontroller, XR2206 Function generator, Liquid Sensor. I. INTRODUCTION In recent few years applications of portable electronic devices are explored extensively. The portability, compactness, accuracy in measurement and cost effectiveness are the motive behind electronic instrumentation design. The microcontroller based instrumentation system plays an important role in miniaturization and hence cost effectiveness of the systems. Due to the use of Microcontroller the modified approach seen in the system design, which results in the instrumentation systems becomes portable, special purpose, wide functioning and economical [1]-[6]. In the present paper the PIC16F628 Microcontroller based portable spectroscopy liquid sensor is developed for measurement of permittivity in liquids. The term dielectric relates to a substance which can act as an insulator by sustaining an electric field. A good dielectric material bears special properties of storing and dissipating electric energy when subjected to electromagnetic field. The dielectric constant gives Physio-chemical composition and structure of the material [7]. The measurement of dielectric constant is very significant in the study of the dielectric behaviour of any liquid. The study of dielectric properties of liquid is useful to understand the structure and molecular interactions in the liquid. Dielectric study of liquid mixtures gives an idea about possible interactions between the constituents such as hydrogen bonding, molecular associations, dipole- dipole and dipole induced dipole interactions [8]. The dielectric study is useful in the wide application area such as pharmaceutical industries, agricultural industries, food industries, instrumentation design industries etc. [9]. 413

2 II. PRINCIPLE The signal frequency of IC XR2206 [10] function generator has been varied in accordance with the timing capacitor C and timing resistor R. The liquid holder cell plays the role of timing capacitor C. The value of resistor R is kept constant. The frequency of function generator depends on the dielectric material inserted into liquid holder cell. And, hence XR2206 function generator oscillates at different frequencies for different liquids. f = 1/RC Hz (1) Where, f - is the measured frequency of a function generator. C - is the capacitance of the cell (with or without liquid). R - is the timing resistor (kept constant) of a function generator. The frequency of XR2206 function generator, without liquid f 0 is measured, after insertion of reference liquid f r is measured, and the frequency f x is measured by inserting an unknown liquid. The measured frequencies are further used to determine permittivity ɛ x of known liquid using the relation as [11]-[12] ɛ x = 1+(f r /f x) [(f 0-f x)/(f 0-f r)] (ɛ r -1) (2) Where, ɛ x - is the dielectric constant of unknown liquid. f r - is the frequency of reference liquid. f 0 - is the frequency of empty cell. f x - is the frequency of unknown liquid. ɛ r - is the dielectric constant of reference liquid. III. EXPERIMENTAL The implemented PIC16F628 microcontroller based portable spectroscopy sensor for liquid integrated witha) Liquid holder, cell b) XR2206 function generator c) Signal conditioning unit d) PIC16F628 Microcontroller e) Seven segment module f) Power supply unit The block diagram and actual experimental photograph of PIC16F628 microcontroller based portable spectroscopy sensor for liquid is shown in figure 1 and 2 respectively. Fig. 1 Block diagram of PIC16F628 microcontroller based portable spectroscopy sensor for liquid. 414

3 A. Liquid Holder Cell The cylindrical liquid holder, cell is used. In this there are two electrodes, the middle electrode and the outer cylindrical electrode. The dielectric medium needs to be in between two electrodes. The dimensions of the cell are, the outer electrode diameter is cm and the inner electrode diameter is about cm. The height of the inner electrode is about 1.07 cm. The liquid sample required for the test is about 0.3 ml. B. XR2206 Function Generator The XR2206 is a monolithic function generator integrated circuit. This function generator produces high quality sine, square, triangle, ramp, and pulse waveforms. The generated waveforms are highly stable. The accuracy in the frequency of the waveforms is very good. It has the facility of modulation in output waveforms. Both amplitude and frequency can be modulated by applying voltage externally. The frequency of operation can be chosen externally over a range of 0.01 Hz to up to 2 MHz. C. Signal Conditioning Unit The amplitude of the sine wave signal obtained from XR2206 function generator is below 3V, which is low so it is necessary to boost the signal voltage for to compatible with Microcontroller, so there is need of signal conditioning. The MPF102 JFET [13] is used as a linear amplifier. The amplifier circuit operates on +9V DC. For to generate threshold voltage the two antiparallel diodes D1 and D2 are used in the front phase of the signal conditioning unit. The 2N4403 PNP transistor is used to produce square wave output. The output produced by 2N4403 PNP transistor is greater than 3.5V, which is required for Microcontroller for to generate the interrupt. The output from the signal conditioning unit further given to pin 9 of the PIC Microcontroller for the counting of frequency. D. PIC16F628 Microcontroller The PIC16F628 Microcontroller is used in the present study. Due to ultimate in programming flexibility, this Microcontroller series is famous amongst the designer. It offers a compact package (less pin count 18 pins), fully featured with ADC (10 bit), RS-485 type USART, high precision voltage comparators and up to 256 bytes of data EEPROM memory. PICmicro FLASH devices operate at below voltage up to 2.0 volts it is beneficial for battery-powered applications. The execution speed is up to 5 MIPS at 20 MHz for high-performance applications. The special feature of the PIC is, supports of self-programming and two-wire In-Circuit Serial Programming (ICSP) over the entire voltage range, without the need of external components [14]. E. Seven Segment Display Module The four bit package common anode types seven segment display is used whose brightness is very good for visualization of the characters. The BC547BP is NPN transistor used as a seven segment driver. F. Power Supply Unit The XR2206, the signal conditioning unit and the PIC16F628 Microcontroller required 18V, 9V and 5V DC power supply respectively. The single power supply module is designed, to fulfil the requirement of three different devices. The 18 V transformer is used which connected to bridge wave rectifier. At the output node of the bridge, the 18V is taken for XR2206 function generator. The IC 7809 [15] voltage regulator is provides 9V for the signal conditioning unit. And the IC 7805 [15] voltage regulator is used to get 5V for PIC16F628 Microcontroller IC. 415

4 Fig. 2 An actual photograph of the experimental setup of PIC16F628 microcontroller based portable spectroscopy sensor for liquid. IV. SOFTWARE The MPLAB IDE [16] is used for to develop the program for counting frequency and display it on seven segment display. The MPLAB integrated development environment is a software that runs on a computer to develop applications for Microchip Microcontrollers. This IDE provides a single integrated environment to develop code for PIC16F628 Microcontrollers. The IDE provides a platform for compile, assemble and link the software using the assembler and/or compiler and linker to convert high level language code such as the c programming language into machine code (Hex) for the PICmicro MCUs. This machine code will eventually become the firmware (the code programmed into the PIC16F628 Microcontroller). The flow chart of required software for PIC16F628 Microcontroller to implement the cost effective spectroscopy liquid sensor is shown in figure 3. Fig. 3 The flow chart of developed software program for PIC16F628 Microcontroller to implement the portable spectroscopy liquid sensor. 416

5 V. SYSTEM CALIBRATION The implemented PIC16F628 microcontroller based portable spectroscopy sensor for liquid is calibrated for the measurement of permittivity of a liquid sample. The calibration and measurement procedure is as follows- Step I- Clean the dielectric sensor cell with acetone, dry it and keep it in a beaker containing air. Step II- Connect the cell to the circuit as shown in figure 2. Step III- Switch on the system. Step IV- The system measures and displays the frequency, the measured frequency in turn of the permittivity of the cell using the equation (2). Note down the frequency value. Step V- Keep the reference liquid (benzene in the present study) in the cell. Step VI- Repeat the steps from (II) to (IV). Step VII- Keep the liquid sample whose permittivity to be measured. Step VIII- Repeat the steps from (II) to (IV). Step IX- Then determine the permittivity of the liquid sample using the equation (2). Step X- For other samples repeat the steps from (II) to (IX). VI. RESULT AND DISCUSSION The performance of the implemented PIC16F628 microcontroller based portable spectroscopy sensor for liquid is studied by comparing its results with other methods. The implemented sensor is tested with some selected samples of liquid at 298K temperature. Along with that for to test the performance of the designed sensor system in binary liquid, the static dielectric constant of Benzene and 1-Propanol binary mixtures also determined. The results are presented in Table I. The figure 4 shows comparative graph of experimental and literature values of dielectric constant for selected liquid samples and figure 5 shows variation in static dielectric constant for binary mixture of 1-Propanol + Benzene at 298 K. The results of the present study are in good agreement with the literature values of dielectric constant. TABEL I EXPERIMENTAL AND LITERATURE VALUES OF DIELECTRIC CONSTANT FOR SELECTED LIQUID SAMPLES. Sr. No. Sample Dielectric constant (Expt. Value) ɛ x Dielectric Constant (Lit. Value) ɛ 1 Heptane [17] 2 Toluene [18] 3 Trichloroethylene [17] 4 Bromobenzene [19] 5 Dichloromethane [20] 6 2-methyl-2- propanol [19] 7 1-Butanol [17] 8 Acetone [21] 9 Ethanol [17] 10 Methanol [17] 11 Nitrobenzene [19] 417

6 Fig. 4 Comparability graph of Experimental and literature values of dielectric constant for selected liquid samples. Fig. 5 Variation in Static Dielectric Constant for binary mixture of 1-Propanol + Benzene at 298 K. VII. CONCLUSION The PIC16F628 microcontroller based cost effective spectroscopy sensor for liquid has been successfully designed and developed. The developed system is used to sense a wide range of dielectric constant. The developed sensor system has been tested for determination of dielectric constant for number of polar and nonpolar liquid samples and also for some binary liquid mixtures. The dielectric values sensed by the designed system were compared with standard literature values, and it is found in good agreement. The calibration and measurement procedure of designed system is very simple, hence no requirement of expertise to work with this sensor system. The precise controls, accurate measurements, fast processing and cost effectiveness are the key significance of the present system. 418

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