Light Intensity and Power Meter Based On LDR and Microcontroller Sheikh Mohammad Nafees, Purnomo Sidi Priambodo Dept. of Electrical Engineering, Faculty of Engineering, Universitas Indonesia Depok Campus, West Java Indonesia. sheikh.mohammad@ui.ac.id,pspriambodo@ee.ui.ac.id ABSTRACT This journal consist of experiments performed to develop a light intensity and power meter utilizing state of the art calibrating method, which can be used to study the interaction between the optical signal and the target, the effect of the environment on propagation of the optical signal, methods to enhance the optical signal, and materials used to generate reliable optical source and to produce sensors with ultra high precision. This experiment uses a light dependent resistor (LDR) as a light sensor to build a light intensity and power meter. The instrument uses microcontroller Arduino Atmega32 chip with 10 bit ADC resolution as a data processing centre. The microcontroller is programmed to calculate and calibrate the input LDR value and display the calibrated data output over LCD screen. The system is also designed and programmed to provide serial communication interface for real time data plotting and data saving over various software like matlab, labview, excel, GUI etc. Keywords : Light intensity, Light sensor (LDR), Analog to digital converter (ADC), Microcontroller, Liquid crystal display(lcd) INTRODUCTION/BACKGROUND A sensor is a device which responds to an input quantity from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal in a form of an electrical or optical signal that is converted to human-readable display at the sensor location or transmitted electronically over network for reading or further processing [1]. During the past two decades, there has been an unprecedented growth in the number of products and services, which utilize information gained by monitoring and measuring using different
types of sensors. The development of sensors to meet the need is referred to a sensor technology and is applicable in a very broad domain including the environment, medicine, commerce and industry. One of the most widely used sensors in present days is known as optical sensor which is applied in almost every field of science [2]. Optical sensors that use photons as sensing elements are increasingly becoming important and relevant in the field of non-invasive diagnostics. The reason is that they have a simple construction, easy to use and relatively inexpensive and least harmful in comparison with tools such as EEG (Electroencephalography), MRI (Magnetic resonance imaging) and FMRI(Functional magnetic resonance imaging) that can be used for research and diagnoses purposes without much investment. In field of medical Science optical sensors are well known as optical biosensors and could be found in almost every portable healthcare device such as Digital heartbeat counter, Blood glucose meter, etc. In order to use optical sensor effectively and efficiently, a controlled optical (photon) source is required to perform required job [3]. Based on the importance of optics in present days, this journal carries the experiments and produce required to design and develop light intensity and power meter. A device performs complex mathematical calculation to detect and study the presence of light in unit of lux, (mw), candela, etc [4], which can help man in various fields and occupation. SCOPE OF PROBLEM Inefficiency in energy usage can be reduced with help of light intensity and power meter. Light intensity meters can be used in optical communication system to measure the intensity of light and power based on other parameters which can be calculated to produce best QoS ratio. Ultra high precision can be obtained in optical biosensors by studying and utilizing optical source effectively. Therefore, topic of this final project is Light power and intensity meter based on LDR and Microcontroller. The main job of light intensity meter is to provide real time intensity data which can be plotted over various softwares like matlab, lab view and etc for their study and employment in different projects with help of microcontroller. This report will explain about the concepts used for designing, simulating, calibrating and applying light intensity, power meter and the component required to build it. Designing of best and accurate light intensity meter is an ultimate goal of this report which later can help other students and professor in their projects and research work. The specification of each element also determines the number of efficiency in application.
OBJECTIVE Develop a light intensity and power meter using LDR sensor and Microcontroller. Find LDR spectral response and generate state of the art calibration equation. Develop a Graphical User Interface (GUI) for real time data plot and saving. SYSTEM BLOCK DIAGRAM/CIRCUITRY Figure(1) shows the simple block diagram of how the light intensity and power meter work. The working mechanism o f a system starts with the intensity of light falling upon LDR sensor. A LDR is light dependent resistor where resistance of a sensor goes down with increasing light intensity [9]. The sensor catches this light and converts it in to a voltage signal with help of voltage divider circuit. Since the voltage output of sensor is in analog form, it cannot be directly fed to microcontroller, because microcontroller requires digital signal to process the input data. For this reason, we use Analog to digital converter which converts the analog output of LDR sensor into digital input, which later feeds to microcontroller. The microcontroller then performs complex mathematical calculation and displays the intensity or power of light over 16 x 2 LCD in unit of (mw). Microcontroller also provides serial communication interface for output data, which can directly upload over interface software (such as Matlab, Labview etc.) for real time data plotting and for other calculations. Figure(2) shows the hardware circuitry. Figure 1: System Block Diagram
Figure 2: Hardware Circuitry While designing hardware few calculations need to be made manually by applying mathematical models, to make sure the system function s properly. Such as, Response time of microcontroller; 1MC =12xT (i) Where: MC stands for machine cycle and T stands for time period. Instruction Cycles; IC = crystal frequency / 12 (ii)
Voltage Divider Resistor [8]; R = (iii) Where: Rmax is sensor s maximum resistance and Rmin is sensor s minimum resistance. Wavelength of a visible light [7]; λ = v / f (iv) Where: λ is wavelength, unit in nano-meter (nm), ν is a speed of light, unit in meter per second (m/s), f is a frequency, unit in hertz (Hz). Sensor Sensitivity [6]; Where: RH= resistance of cell at light level H, ρh= sheet resistivity of photoconductive film at light level, w= width of electrode gap, l = length of electrode gap EXPERIMENT POWER METER In Figure (3) shown, is a workbench setup used to perform an experiment to collect the data required for Power meter modeling and calibration. Figure 3: Power Experiment Setup
In this experiment, a sensor which is LDR is kept close in a straight line and fixed at distance of 0cm from LED (optical source) to receive maximum amount of radiated energy in mw. With increasing light intensity the resistance of a sensor goes down. These varying sensor values are then recorded in a computer or laptop with help of microcontroller for further analysis and calibration. The data obtained by performing experiment mentioned above is collected and shown in Table (1). Table (1) and Graph (1) shows the data collected and plotted for red LED and similarly for green, blue and white in table and Graph (2), (3) and (4). Table 1: Red LED (Power Meter) Graph 1: Red LED (Power Meter)
Table 2: GREEN LED (Power Meter) Graph 2: Green LED (Power Meter) Table 3: BLUE LED (Power Meter)
Graph 3: Blue LED (Power Meter) Table 4: White LED (Power Meter) Graph 4: White LED (Power Meter)
SPECTRAL RESPONSE The spectral response of a LDR sensor is one of the most important parameter need to be calculate to make sure that sensor responses to almost every visible light color ranging from Blue to Red, 400-700 nanometer wavelength. The spectral response of a LDR in use can be seen by plotting a Graph (5) shown below. The values required to plot a Graph is collected from Table (1, 2, 3, 4) at fixed sensor s values and can be seen in Table (5). Table 5: (Spectral Response) Graph 5: (Spectral Response) From Graph (5) above its clear that LDR have a wide spectral response range between 450 650nm which is similar to human eye, therefore can be used in light intensity and power meter development. EXPERIMENT INTENSITY METER In this experiment, a sensor is kept at distance of 1cm from LED (optical source) and the distance is gradually increases with increment of 1cm every time, collecting radiated energy at different points. A LDR is light dependent resistor where resistor of a sensor goes
down with increasing light intensity. These varying Sensor values are then recorded in a computer or laptop with help of microcontroller for further analysis. A system setup for experiment can be seen in Figure (4), while data collected can be seen in Table (6). Figure 4: Intensity Experiment Setup The data obtained by performing experiment mentioned above is collected and shown in Table (6) and Graph (6), (7), (8) and (9) are plotted based on data collected below. Table 6: All LED (Power Meter)
Graph 6: Distance Vs Light (Red LED) Distance Vs Light Intensity Light Intensity (mw) 60 50 40 30 20 10 0 0 5 10 Distance (cm) Red LED Graph 7: Distance Vs Light (Green LED) Distance Vs Light Intensity Light Intensity (mw) 80 60 40 20 0 0 5 10 Distance (cm) Green LED Graph 8 : Distance Vs Light (Blue LED) Distance Vs Light Intensity Light Intensity (mw) 80 60 40 20 0 0 5 10 Distance (cm) Blue LED
Graph 9 : Distance Vs Light (White LED) Distance Vs Light Intensity Light Intensity (mw) 80 60 40 20 0 0 5 10 Distance (cm) White LED CALIBRATING PROCEDURE To obtain best approximated result from Power and light intensity meter, 3 calibrating equation have been generated with help of data obtained in table 1, 2, 3, 4 & 6.The equations generated with help of Microsoft excel in power, polynomial and exponential forms. These equations are then compared with one another by testing and the equation with best results is then selected for a data processing. Comparison between the equations can be seen in Table (7) and (8) below. Table 7: Calibration (Power Meter)
Table 8: Calibration (Intensity Meter) RESULTS By analyzing Table (7) and (8) for power and intensity meter, we can see that best approximated results can be obtained with help of power and exponential equation but power equation provides least error percentage, with over all accuracy of +/- 1mW.Therefore utilizing power equation for a data processing is a best choice. Results can be seen in Table (9) for Power meter and Table (10) for Intensity meter. Table 9: Light Power Meter (power eq.)
Table 9: Light Intensity Meter (power eq.) GRAPHIC USER INTERFACE For simplicity in modifying formula and to obtain further accuracy in calculation, a graphic user interface is designed with help of processing software. The GUI provide user with a system functioning as a real time data plotter and data saver in (.txt or.csv) format for future analysis. Creating a GUI provide an advantage over microcontroller where memory is a problem and coding must be kept simple for the sake of system performance and noises (like heat and clock speed).the GUI designed can be seen in Figure(5) below and programming algorithm flow chart for microcontroller and GUI can be seen in Figure (6). Figure 5: Graphic User Interface
Figure 6: Algorithms for Microcontroller and GUI CONCLUSION After going through the calibration phase, an analysis proves that, the power equation is a state of the art calibrating equation for obtaining a best linear relationship between optical source and sensor. Although LDR have a nonlinear spectral response, but can be used for the measurement of light intensity and power for different colors and wavelength ranging between 400-700 nm. A microcontroller with greater ADC bit rate provides point to point accuracy in data processing with higher resolution. The LEDs on the other hand should not be used as a calibrator, since they lack of fixed calibration coefficients. Fore, it is proposed
to use a halogen light source which is equipped with mono-chromate providing better accuracy in calibration. REFRENCES [1] Blais,F. (January 2004). Review of 20 Years of Range Sensor Development. Published in the Journal of Electronic Imaging, 13(1): 231 240. NRC 46531. http://foto.hut.fi/opetus/295/pg_course2008/beraldin/nrc-46531.pdf [2] Rinken, T. (March 13, 2013). State of the Art in Biosensors - General Aspects (ISBN 978-953-51-1004-0). Chp 5, 11. Publisher: InTech. http://www.intechopen.com/books/state-of-the-art-in-biosensors-general- aspects [3] Research India Publication.(2009). Sundararajan, M. Optical Sensor Based Instrument for Correlative Analysis of Human ECG and Breathing Signal. International Journal of Electronic Enginee-ring Research. Vol. 1, 287-298. http://www.ripublication.com/ijeer.htm [4] Rose, B. (2000). Special section on Optical Sensors. Page-9, Publisher: ADC Denmark Aps, Ryttermarken 15-21. http://www.dops.dk/pictures/pdf/archive/2000/00_4_art2.pdf [5] ite.gravitech.us/arduino/nano30/atmega328datasheet.pdf [6] http://optoelectronics.perknelmer.com/content/applicationnotes/app_photocellintrodu ction.pdf
[7] Saleh, B.E.A. & Teich, M.C. (April 3, 1991). Fundamentals Of Photnics, John Wiley & Sons, Ltd. Chp 17. [8] Robert L Boylestad, Louis Nashelsky, Electronic Devices And Circuit Theory, Tenth Edition,Prentice Hall,2009. Chp 1, 2, 16 [9] Bazir, M.A.A, Ramli, F.K, Nur S. Ibrahim, S.N, Pying, Y.L, & Rokhani, Z.F. (2011). Mobile Robot Guidance using Light Dependant Resistor Device. IEEE 07th International Colloquium on Signal Processing and its Applications. 978-1-61284-413-8/11. fakhrulz@eng.upm.edu.my