Indian Journal of Science and Technology, Vol 9(16), DOI: 10.17485/ijst/2016/v9i16/88115, April 2016
ISSN (Print) : 0974-6846 ISSN (Online) : 0974-5645
Simulation and Implementation of Angular Displacement Measurement System for Antenna Positioning A. A. Mulla1* and P. N. Vasambekar2 1
Department of Electronics, Yashwantrao Chavan College of Science, Karad - 415124, Maharashtra, India;
[email protected] 2 Department of Electronics, Shivaji University, Kolhapur - 416004, Maharashtra, India
Abstract An angular displacement measurement system has been designed. System is simulated by using free and open source Scilab. The overall minimum, real time system is designed around an 8-bit cost effective, MCS51 microcontroller 89C2051. A high precision wire wound potentiometer serves as an angular displacement sensor. The digitized sensor output form ADC0804, after processing is displayed on LCD. The system is minimized by connecting ADC in free running mode and LCD in 4-bit mode. The system is tested for measurement of an angular displacement in the range of 0-180°. The results of simulation and the experimental measurements are in good agreement. The system is suitable for angular displacement measurement for antenna positioning.
Keywords: Angular Displacement, Angle Measurement, Antenna Positioning, Minimum System, Scilab
1. Introduction Mechatronics, the fastest growing ield in technology, is a combination of mechanical, electronic and information technology. It is useful in robotics and automation. he antenna positioning system is one of its applications. hese systems are useful for directing antennas towards moving signal source. During antenna positioning the antenna is steered mainly in the azimuth and/or elevation directions. To steer about these axes stepper motors1–5, DC motors1,6, geared DC motors7, Brushless DC (BLDC)8 and DC servo motors9 are used. For accurate and precise positioning the precise measurement of the angle of positioning is necessary. It is required mainly when the system is developed around stepper motor, DC motor, BLDC, BLAC or DC geared motor as these motors are open loop type and have no inbuilt inal position control facility as that inservo motors. In the present communication the angular displacement measurement system, simulated by using *Author for correspondence
Scilab and its experimental implementation around 89C2051 microcontroller is reported.
2. System Modeling and Hardware he block diagram of the system is presented in Figure 1. A precision wire wound potentiometer is used as an angular displacement sensor. It produces DC output voltage proportional to the input angular displacement. his output voltage is in suitable form of input range of ADC used, therefore the system does not need more signal conditioning stages. he 8-bit ADC0804 converts the analog signal into the digital form. he microcontroller 89C2051 reads data from ADC, processes it and displays on LCD.
2.1 Angular Displacement Sensor he angular displacement can be measured by using resistive, capacitive, inductive, encoder, magnetic,
Simulation and Implementation of Angular Displacement Measurement System for Antenna Positioning
Angular Displacement Sensor (Potentiometer)
Analog-to-Digital Converter (ADC0804)
LCD (16 X 2)
Microcontroller (89C2051)
Figure 1. Angular displacement measurement system.
optical iber and piezoelectric sensors. A resistive potentiometer sensor is mostly used in antenna positioning applications10–13. he use of a potentiometer in linear and angular displacement measurement is one of the simplest and cost efective technique14. he output voltage of the potentiometer is dependent on the input angular displacement as well as exciting dc voltage source13,14. he encoder is also useful in angular displacement due to its precision and accurate measurement. However, it is more expensive than potentiometers. In the present system a single turn, high resolution,special ‘O’ type shat, wire wound potentiometer with 10K resistance, 1% linearity, 1.5 watt power rating and end stop at 180° is used as an angular displacement sensor. It produces an output of 0-5V for 0-180° input angular displacement when a 10V DC supply voltage is applied to it. he output of this device is coupled to the ADC0804.
2.1.1 Mathematical Modeling of Potentiometer Figure 2 shows the rotary potentiometer. he changed resistance of the rotary potentiometer with respect to angular displacement is mathematically represented as, RPB=(RAB/(Pmax.-Pmin.)) × P
(1)
Were, RPB=Resistance between P and B,RAB= Resistance between A and B,Pmax.= Maximum angular displacement of potentiometer, Pmin.= Minimum angular displacement of potentiometer. he output voltage (VPB) at the potentiometer output is given by, VPB=(RPB/RAB) × Vcc
(2)
Were, VPB = Voltage between points P and B, Vcc= Exciting DC voltage across the potentiometer.
erates a clock period of 110 µs. To reduce pin count of the microcontroller during interfacing the ADC is connected in free running mode in the present system. hus, chip selectand read pins of the ADC are grounded and the chip is always ready to transfer the converted data. he interrupt request pin checks the statues of ADC. he writepin is used to apply start of conversion pulse to the ADC. he interrupt request and write pins are connected to each other. A switch is connected between these pins and ground. It is essential to press thisswitch ater system supply is turned ON. he Vref/2 pin is kept open to ensure the input range of ADC to be 0 to 5 V with step size of 19.53 mV15. he eight data lines (D0-D7) of ADC are used to send converted data to the microcontroller.
2.2.1 Mathematical Modeling of ADC he digital output of ADCmainly depends on analog voltage span, resolution and step size. For analog to digital converter, Step Size = (Analog Voltage Span) /2Resolution Step Size =(Vmax. – Vmin.) /2Resolution
(3)
Were, Vmax and Vmin are maximum and minimum allowable voltage applied at input pin Vin(+) and Vin(-) pin of ADC. he ADC output is given by, ADC output = (Applied Analog Voltage) / Step Size (4)
2.3 Liquid Crystal Display he 16 × 2 LCD model HD44780 is used to display measured angle. It has three control lines (RS, RW and E). he 4-bit LCD mode chosen allows less number of pins to display data/command. herefore, only four lines D4 to D7
2.2 Analog-to-Digital Converter For digitizing the analog signal, Texas Instruments successive approximation type 20-pin, CMOS, having 8-bit resolution ADC0804 is used. It has 100 µs conversion time and has an on chip clock generator. he combination of 15 K resistor and 100 pF capacitor gen-
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Figure 2. Rotary potentiometer.
Indian Journal of Science and Technology
A. A. Mulla and P. N. Vasambekar
are used and D0 to D3 are grounded. Compared to 8-bit mode, the display speed of this mode is lower.
2.4 Microcontroller Atmel low cost, 20-pin, 8-bit microcontroller 89C2051 is used in this system. It has 2K programmable lash memory, 128 bytes of RAM and 15 programmable I/O port pins16. It is mostly used for simple and small size structure. It is mainly used during cost efective system development17. he port P1 is used for reading the data from ADC. Seven pins of P3 are coupled to the LCD. he pins P3.0 to P3.3 are connected to the data lines D4 to D7 of LCD and P3.7, P3.5 and P3.4 are connected to control lines RS, RW and E respectively. he complete circuit diagram of the system is presented in Figure 3.
2.4.1 Mathematical Modeling of Microcontroller he microcontroller reads the datafrom ADC using P1, processes it and converts angular displacement into suitable decimal form (degree). During data processing, the microcontroller executes the following equation. D = (P1/10)∗7 + ((P1%10)∗8)/10
(5)
Were, D is output angular displacement, P1 is ADC output read by P1, ‘/’ is division operator, ‘∗’ is multiplication operator and ‘%’ is modulo division operator.
3. Program Code Developed system is supported by two program codes: • Simulation Code with Scilab. • Real Time System Program Code.
Figure 3. 89C2051 based system.
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Simulation and Implementation of Angular Displacement Measurement System for Antenna Positioning
3.1 Simulation Code with Scilab he simulation sotware is developed by using Scilab. It is free and open source sotware useful in engineering and scientiic applications for numerical calculations18. he code developed for simulation is as follows: //-------------------------------------------------------------//Simulation of Angular Displacement Measurement System using Scilab for 0-180° //-------------------------------------------------------------RAB=10000, //Used Potentiometer Value(Ω), Pmax=360, //Maximum Rotational angle of the potentiometer(°) Pmin=0, //Minimum Rotational angle of the potentiometer(°) VCC=10, //DC excitation to the potentiometer (V), Vmax=5, //Maximum analogueat the Vin(+) of ADC for Vref/2 open Vmin=0, //Minimum analogue input voltage(V) at the Vin(+) of ADC for Vref/2 open Resolution=8, //Used ADC has resolution 8-bit P =(0:5:180) //System tested for the input angular displacement range 0-180° with step 5° RPB=(RAB/( Pmax- Pmin))∗ P //From equation 1of potentiometer VPB=(RPB/RAB)∗VCC //From equation 2 of the potentiometer Step_size=(Vmax-Vmin)/2^Resolution //ADC step size from equation 3 Y=int(VPB/Step_size) //ADC output in int form it does not contains loating from equation 4 //8051 read ADC data Y and perform the following operation, display angular displacement on LCD D=int((int(Y/10))∗7+(modulo(Y,10)∗8)/10) //D=Output Angular Displacement //#int-command integer for quiescent and modulo- command for remainder #int and modulo commands are used as 8051 does not store fraction, it stores result in quotient and remainder for division operation.
3.2 Real Time System Program Code he system sotware is developed in Assembly Language Programming (ALP). It is small size hex code. he steps involved in it are:
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Figure 4. Potentiometer output.
Figure 5. System output.
1. Initialization of stack pointer and bank selection 2. Initialization of Port 1 as an input port to read data from ADC 3. Initialization of the LCD by adding delay and sending various commands of LCD: 4-bit mode, display on cursor on, clear LCD, Shit cursor right, cursor positions 4. Read ADC data using Port P1. 5. Display result on LCD using P3 ater processing the data. he output of ADC will be FFH(255) at 180° and 00H(0) at 0° if Vref/2 pin is open. Equation (5) is used to convert the ADC data into suitable degree form.
Indian Journal of Science and Technology
A. A. Mulla and P. N. Vasambekar
he instructions used for solving Equations (5) are as follows. i)//Solving equation (P1/10)∗7 operation MOV A,P1 //Read data form ADC MOV R0,A //Safe store ADC data at R0 MOV B,#10 DIV AB MOV B,#7 MUL AB MOV R1,A //Store result of the operation (P1/10)∗7 at R1 ii)//Solving equation ((P1%10)∗8)/10 operation MOV A,R0 MOV B,#10 DIV AB MOV A,B //remainder in B copy into A MOV B,#8 MUL AB MOV B,#10 DIV AB ADD R1 //add result of (ii) and (i) step 6. Considering the deviation of potentiometer output in the range of 0°–35°, addition of correction factor of 2° in the result obtained in step 5. 7. Ater converting into ASCII form, displaying the result on LCD. 8. Repeating continuously steps 4, 5, 6 and 7.
4. Simulated and Experimental Results Using Scilab, simulated potentiometer output voltage is obtained for the angular displacement between 0°–180° in steps of 5°. he shat of the potentiometer was positioned by rotating the knob in diferent input angles between 0°–180° in steps of 5° and the developed potentiometer DC output voltage was measured with multimeter. he input angular displacement of potentiometer at various angular positions was read on protractor (coupled to potentiometer). he plot of input angular displacement versus potentiometer output voltage is presented Figure 4. he simulation results for the same parameters are also presented in same graph for comparison. From this igure it can be noticed that the experimental and simulated response are in good agreement. From the plot
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the deviation of potentiometer output voltage in the range of 0°–35° can also be noted. he plot of measured input angular displacement (in the range of 0°-180° in steps of 5°) on protractor versus output angular displacement read on LCD is presented in Figure 5. It can be seen that the experimental results agree well with simulated results in the range of 5° to 175°. hus the developed system is found to be most useful for the input angular displacement in the speciied range.
5. Conclusion he real time system is developed for measurement of angular displacement using rotary resistive potentiometer having lower cost than rotary sensor with 20 pin 89C2051 microcontroller. It is also simulated by using open source sotware Scilab. he simulated and experimental results agree well. he system can be useful for the positioning the antenna in the azimuth/elevation in the angular range of 5° to 175°.
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