An Improved Operational Amplifier iLab with a More Realistic
Contents
1. c aoe Click Run buttonto submit to Lab Server for execution Client automatically checks for result L ret ready YES download result switch to oscilloscope view and press power button to view output waveforms answer questions and carry out other consequent assignments as specified in laboratory manual Fig 7 flow chart showing sequence of a student s activities during a laboratory session By far the most time consuming aspect of working on the client interface is the connection of the various operational amplifier circuits which students must carry out by drawing multiple segments of wires to connect different points on the breadboard Figs 8a c show different node connection steps a student could go through in configuring an inverting amplifier on his client computer using the datasheet of the LM741 op amp IC Each view indicates the circuit diagram of an inverting amplifier shown on the interface Circuit Selector The student uses this as a guide to connecting up the correct operational amplifier circuit Once a circuit has been constructed the student must then verify that it is a valid circuit by clicking the verify circuit button The run button which is used to submit the experiment for execution is disabled until a circuit has been verified in this manner Fig 9 shows the resulting screen after the inverting amplifier circuit connected above was verified The DFS algorithm reduced the student2. iterations featured fixed sets of nodes and circuit branches All that the student using either design needed to do was to determine which branches to add or remove from the circuit Such an artificial constraint is not experienced in a real life lab Finally the new design provides a backend circuit that is much easier to expand and therefore more engaging for the students In this paper we first provide a brief sketch of the first two generations of the OAU OpAmp iLab so as to allow easy contrast of their features with those of the new version We then describe the architectural features of the new iteration Subsequently a detailed discussion of the use of the new lab in a sample student experimentation session setting is undertaken The paper then details an account of the use of the lab in a credit awarding course as well as the results of the assessment of students use of the lab II Previous Generations of the OAU OpAmp iLab The first generation of the OpAmp iLab offered an interface where students modified an existing operational amplifier circuit by drawing wires to connect a small set of pre positioned nodes Fig la The interface was implemented as a C browser control The back end system under test SUT was a dozen impedance operational amplifier circuit mounted on a National Instruments Educational Laboratory Virtual Instrumentation Suite NI ELVIS prototyping board Input signal generation and data acquisition was achiev
3. On Networked Learning In A Global Environment Berlin Germany May 2002 Gerado Viedma Isaac J Dancy and Kent H Lundberg A web based Linear Systems iLab Proceedings of 2005 American Control Conference Aina O I 2003 Alternative Modes of Financing Higher Education in Nigeria and Implications for University Governance in J Babalola and B O Emunemu Eds Issues in Higher Education Research Evidence from Sub Saharan Africa Association of African Universities and Higher Education Research Policy Network Accra Olowokere D Ayodele K P Kehinde L O Jonah O Ajayi T O Akinwunmi O O Realistic Looking Interfaces in Search of the Best Ergonomic Metaphors for Remote and Virtual Laboratory Interfaces Proceedings of the ASEE Annual Conference and Exposition June 2008 Pittsburgh V Judson iLab A Scalable Architecture for Sharing Online Experiments ICEE Florida USA 2004 K P Ayodele et al Development of an Operational Amplifier Virtual Laboratory Based on iLab Architecture and NI ELVIS in ASEE Annual Conference and Exposition Pittsburgh PA 2008 pp AC 2008 1098 Luis Gomes Javier Garcia Zubia Advances on Remote Laboratories and e Learning Experiences Bilbao University of Deusto 2007 v 6 p 297 309 Del Alamo J A Chang V Hardison J Zych D and Hui L 2003 An Online Microelectronics Device Characterization Laboratory with a Circuit like User Interface Proceedings of the Interna
4. s connections to its minimal form and then determines whether it fitted one of the standard operational amplifier circuits Figs 10a c show some of the errors a student can encounter when using the lab Fig 10a shows a wrong inverting amplifier connection at pin7 of the LM741 The student has connected R and Vout to pin 5 instead of pin6 Hence the run button was not enabled and the experiment could not be forwarded to the lab server for execution Fig 10b show a typical error a student can get when he is trying to do something inappropriate on a breadboard like connecting a wire across the same node or trying to make a slant connection Note that a slant connection is not necessarily invalid but unprofessional Fig 10c shows what a student gets when the remote lab could not be reached or is unavailable Once the circuit is verified the student can click on the run button to submit it for execution The client then monitors the server for completion of execution The student can then go to the oscilloscope screen to view the output waveform once the results are downloaded Fig 11 shows the oscilloscope displaying the signals from the SUT The Zoom button toggles zoom in and zoom out effect te ai fn a sassy a vaa aes Reese 44 seg a ee ee qumenesser gt os HE E Fig 8 sample steps in the connection of an inverting amplifier circuit Inverting Amplifier s successfully connected Fig 9 screen aoe sh
5. to the laboratory device for execution and a purpose built LabVIEW dynamic link library dll that serves as the entry point to the NI ELVIS experimentation board The remote re configurability of the op amp circuit was achieved through a switching matrix using an NI SCXI 1169 100 channel single pole single throw SPST switch array and a web service that allows the switches in the array to be remotely controlled The switching matrix web service implemented in Microsoft Net Framework controls the NI 1100 chassis which houses the NI SCXI 1169 and in turn switches on the desired switches to configure the circuit Lab Server Fig 6 shows a pictorial representation of the lab server and shows how it interacts with the SUT and other hardware The experiment engine polls the lab server database for new experiment When an experiment has been submitted to the lab server for execution the experiment engine loads the next experiment on the MS SQL database based on the priority and forwards the experiment configuration to a Microsoft Net switching matrix web service used to implement the remote re configurability of the op amp circuit This in turn closes the required switch to form a particular operational amplifier circuit configuration Once the circuit is set the experiment engine sends the signal configuration received from the lab client through the purpose built LabVIEW dll to the NI USB 6251 connected to the NI ELVIS workstation which executes t
6. AC 2012 4608 AN IMPROVED OPERATIONAL AMPLIFIER ILAB WITH A MORE REALISTIC LOOKING INTERFACE Mr Babatunde Isaac Ishola Mr Olawale Babatunde Akinwale Obafemi Awolowo University Prof Lawrence O Kehinde P E Obafemi Awolowo University Ile Ife Nigeria Professor Kehinde has been a Professor of Electronic and Electrical Engineering at the Obafemi Awolowo University Ile Ife Nigeria since 1988 He was the Director of ICT as well as the founding Principal Investigator of the University s iLab group in collaboration with MIT USA Currently he coordinates a State Research and Educational Network His present work includes developing virtual and remote labs for students experimentation He just concluded a 3 year visiting Professor job at the Texas Southern University Houston Dr Kayode Peter Ayodele Mr Oluwapelumi Olufemi Aboluwarin c American Society for Engineering Education 2012 AN IMPROVED OPERATIONAL AMPLIFIER ILAB WITH A REALISTIC LOOKING INTERFACE Abstract Realistic interfaces for iLab based operational amplifier experiments have previously been reported Motivated by experiences and students feedback gathered in the past an even more realistic interface for op amp experimentation using iLab technology is hereby presented The emphasis in the current work was on the design of a new client and consequently the system under test SUT remains largely unchanged from previously reported iterations of the lab The only notab
7. as Computer Aided Design CAD or Electronic Design Automation EDA software simulations and remote and virtual laboratories have been explored to overcome these difficulties Remote laboratories in particular have benefitted from some attention from educators and engineering education 8 12 researchers because of some advantages they possess One of the remote laboratory frameworks is the MIT iLab shared architecture which provides a suite of software tools that serve as a framework for quick and easy laboratory development and deployment It hides the details involved in network communication from the developer and provides robust infrastructure for administration and storage which lets the developer focus on the actual experimentation setup The iLab topology is three tiered and includes the Lab Client gt 7 The Lab Client is a software application that runs in a Service Broker and the Lab Server browser It provides an interface that allows the user to interact with the remotely located laboratory equipment The Service Broker is a web application that takes care of the communication between the Lab Server and the Lab Client In other words all communication between the Lab Client and the Lab Server is through the Service Broker The Lab Server is remote computer that interacts with hardware equipment that executes the experiments forwarded to it from the lab client A number of iLabs have been developed and deployed both in an
8. d outside of MIT This paper presents a new version of the operational amplifier iLab OpAmp iLab developed at Obafemi Awolowo University OAU Nigeria gt The lab was originally developed for use in an introductory course on operational amplifiers for third year students of Electronic and Electrical Engineering in the university but has been used by other groups of students It allows students to investigate the properties of the different configurations of an operational amplifier While both previous iterations of the lab were enthusiastically received by students it was necessary to develop a new version to address three issues Firstly one of the major complaints Nigerian educators have about the use of remote laboratories is that such labs allegedly cannot be effective in getting students to really understand laboratory apparatus because they do not offer student any kinaesthetic stimulation While there is some basis to the concern of such educators a previous study indicated that creative use of realistic interface metaphor could help in giving students a laboratory experiences closer to that of a real lab 7 Consequently the first reason for the new iteration of the OpAmp iLab was to provide an interface metaphor that is more similar to what a student might encounter in a real lab Secondly this iteration was developed to provide students with more circuit design flexibility than the previous two iterations Both previous
9. ed through the NI DAQm x signal processing library and an NI 6251 data acquisition card The iLab was severely crippled because the version of NI DAQmx available at the time throttled available data acquisition bandwidth whenever simultaneous input and output operation were attempted Hence the lab could not generate input signals faster than 16 Hz for the operational amplifier circuit while simultaneously sampling the output The resulting output signals were plotted on a graph using volt per division and timebase calibrations similar to a real oscilloscope as shown in Fig 1b 4 Opamp Lab Microsoft Internet Explorer Oj x 4 Opamp Lab Microsoft Internet Explorer Oj x File Edit wiew Favorites Tools Help ay File Edit wiew Favorites Tools Help ay Q pack x a A Search Favorite O G H Q Back x a A A seach ge ravorites O G H Address http ilab oauife edu ng OpampLabClient Default aspx couponID 526 amp passkey Y eg Go Links Address http siilab cauife edu ng OpampLabClient Default aspx couponID 526passkey eg Go Links oC Please select new Lab configuration here Differentiator 5 hae Signal Source Oscilloscope show display download data Submit j I Trusted sites Z Done Trusted sites a b Fig 1 Interface of the first generation OpAmp iLab showing a the circuit connection window b the signal window showi
10. es are connected the client computes the corresponding switch pattern using the DFS algorithm For example Fig 5 shows the configuration for an inverting amplifier on the lab client interface as connected by a student during a typical lab session This is realized on the lab server by closing switches 1 3 4 6 in Fig 4 while other switches are opened vy Inverting R1 RF Non Inverting wo Sw TO Wi O 2 6 Unity 3 PS Q swe V AN Difference Fig 4 A reconfigurable operational amplifier circuit that implements four op amp configurations Table 1 Switching Table for four experiments Switch Conditions s9 510 close jopen jclose close open close open n n n close jopen close jopen close jopen j close jopen jopen open open close jopen open open jopen close open jopen close open close close open jopen open close close close 12V4 ss Cable for Vae os pune vee eee oa ora oe V lt q _ ee eee ee ee ee ee LM741 operational amplifier Fig 5 An inverting operational amplifier as connected by a student Signal acquisition and processing was achieved through the NI USB 6251 DAQ card connected to NI ELVIS experimentation board on which the operational amplifier circuit was set It was controlled by the experiment execution engine a C program that controls the execution of experiment by selecting experiment specification from an MS SQL database forwarding it
11. he experiment The output of the system is sent through the same channel back to the experiment engine which inserts the result into the MS SQL database The result when requested by the lab client is used to plot the output waveform on the virtual oscilloscope Switch Matrix Switching Matrix Web Service Experiment Execution Engine Loaded Experiment 42 Finished running Experiment Loaded Experiment 43 Finished running Experiment LabVIEW dil cee E T im a MS SQL Database Fig 6 Pictorial representation of the Lab Server showing how the various components are connected a LabVIEW dll The SUT was mounted on the NI ELVIS which is used for the signal acquisition and processing NI ELVIS hardware is controlled by LabVIEW a software suite also from National Instrument The lab client was however not designed with LabVIEW Therefore to enable the experiment engine written in C to control the LabVIEW VI the VI was converted to a dll function and exported into C so that the VI can be controlled using a C method call The LabVIEW dill approach made it possible to process signals of frequencies ranging from 5Hz to 250kHz which is the same frequency range supported by NI ELVIS function generator 10 as against the NI DAQmx approach which could only process signals between OHz to 16Hz b Switching Matrix NI SCXI 1169 1000 DB 30 The Switching Matrix see fig 6 comprises of a matrix of switches controlled o
12. le exception is that in the current SUT the operational amplifier circuit also allows the construction of a difference amplifier As before remote configurability and data acquisition are achieved through a 100 channel switch array and a NI USB 6251 DAQ card controlled by the experiment engine respectively The realistic looking interface of the circuit is implemented using Adobe Flex technology It utilizes a metaphor fabricated around realistic images of the breadboards electronic components and instruments To allow the flexibility available in a real lab where students can utilize an arbitrary set of breadboard nodes in wiring up a particular circuit the client utilizes a depth first search algorithm to construct circuits from an arbitrary number of student node to node connections An attempt was made to prevent student disorientation by employing the use of intuitive control actions to zoom and pan the view as well as hide interface elements as desired Lab assessment was done in two phases First a questionnaire was administered to students after using the lab Their responses were compared with those for a previous generation of the operational amplifier lab Secondly a small study was carried out to verify a previous argument that realistic interfaces improved students laboratory experience The results of the study are discussed and attempts are made to extend the implications to other remote laboratories Furthermore the performance
13. nal returned from the improved OpAmp iLab indicating wide frequency range VI Conclusion The improved OpAmp iLab with a very realistic interface a remote laboratory based on the MIT iLab shared architecture is the third iteration of the OpAmp iLab at OAU Nigeria The lab client built with the Adobe Flex Framework mimics the real components devices and equipment to make the remote laboratory experience as close to real life as possible This was intended to help students who use the OpAmp iLab relate such experiences in handling real systems And as the result of the study shows the realistic interface to a reasonable extent aided the students understanding of the experiment Our hypothesis is therefore valid realistic interfaces improve students laboratory experience VII Acknowledgement The authors would like to thank Jud Harward and members of the Center for Educational Computing Initiatives CECI at the Massachusetts Institute of Technology for assisting with various aspects of the research The research was funded by a grant from the Carnegie Corporation of New York REFERENCES 1 I Gustavsson Remote Operation and Control of Traditional Laboratory Equipment Sweden 2006 10 11 12 13 14 Del Alamo J A L Brooks C Mclean J Hardison G Mishuris V Chang And L Hui The Mit Microelectronics Weblab A Web Enabled Remote Laboratory For Microelectronics Device Characterization 2002 World Congress
14. ng input and output waveforms The next version of the OpAmp iLab used an Adobe Flash based client gt The use of a 2D vector based client provided more flexibility than C used in the first interface and allowed the representation of the backend as a printed circuit board PCB on which various components of the circuit were laid out Fig 2a The lab used a modified version of the MIT iLab architecture The Flash OpAmp iLab omitted the Service Broker thus allowing direct client to server communications using web services The block diagram of the Flash OpAmp iLab is presented in Fig 2b Like its predecessor the lab server used a dozen impedance operational amplifier circuit mounted on a NI ELVIS board and NI DAQmx library for data acquisition and signal processing ae web service experiment execution engine internet intranet client database Dozen impedance hardware backend server b Fig 2 a Client interface of the Flash OpAmp iLab b Block diagram of the Flash OpAmp iLab HI The Improved Operational Amplifier iLab Based on the responses of users of the previous implementations of the OpAmp iLab and the result of the previous study on the effect of interfaces gt 7 an improved version of the OpAmp iLab has been developed The new OpAmp iLab utilizes the complete MIT iLab architecture as shown in Fig 3 Lab Server Service Broker Lab Client Lab PA A LS Web Internet I
15. nternet rn Device Execution Service latent Batched iLab SB TERA Built with Engine Adobe Flex Switching service web service Service Lab Server Database Broker Switch Database Matrix Fig 3 The improved version of the OpAmp iLab utilizing the complete MIT iLab Architecture The Lab Client The Lab Client was developed with Adobe Flex 3 0 a framework for developing rich internet applications RIA Adobe Flex was chosen for the interface because Flex controls are rendered in browsers as Adobe Flash movies and more than 99 of the computers on the Internet already have the necessary plugin The interface shown in Figures 8 12 presents the picture of a breadboard with components mounted on it and allows the student to set up any of the operational amplifier configurations by drawing wires to connect components on the breadboard The components include an operational amplifier integrated circuit IC colour coded resistors and connecting wires The interface also includes the picture of a function generator and oscilloscope that that allows the control of the remote equipment by operating the controls knobs and buttons on the client virtual interface Hence a student who wants to use the lab must know how to set up an operational amplifier circuit use a datasheet understand resistor colour coding and use a breadboard function generator and an oscilloscope This interface is a closer approximation to a real life laborator
16. of the LabVIEW dll approach to experiment control is compared with a previous approach using the NI DAQmx library Keywords iLab Adobe Flex operational amplifier realistic interface RIAs DFS I Introduction Physical experiments are indispensable for developing skills to deal with physical processes and instrumentation Experimentation has therefore long been an integral part of engineering education due to the fact that it bridges the gap between theoretical and practical knowledge Students perform experiments to verify the theories taught in class and ultimately relate the laboratory and real world experience The latter is crucial to a student of engineering as he must be able to identify and operate equipment relevant to his discipline The use of traditional laboratories in curricula however presents educators with unique attendant challenges Notable among these is the chronic underfunding of higher institutions of learning particularly in 14 This is compounded by the rising cost of laboratory developing countries such as Nigeria equipment and increasing student enrollment which implies an increase in the amount of laboratory space required to handle the large student populations Furthermore some items of equipment are so sensitive and expensive that they cannot be made available to large student classes for fear that they would rapidly be damaged Alternative mechanisms for delivering student laboratory experiences such
17. owing message to student when an inverting amplifier circuit was successfully constructed and verified EEEE ee ee ee ee ee eee eee eee eee See ee eee eee ee O 1 af E a wrong connection Pin7 Jo EEEE Peete eee TeReaEGE TEETE Fig 10 Error screens a student might encounter when he tries to verify or submit an experiment Edit View Insert Format Help J Default aspx couponID 1048 amp passkey 32432419076 7632 Google Chrome Q 62 173 43 96 FlexOpampClient Default aspx couponID 10488 amp passkey 324324190767632 app 875e8 amp 7b5f selectedIndex 2 Comman ww ED t WordPad upon ocument WordPa 209 12 55 PM Monday For start em 22 E Untitled Notepad 26 Windows Explorer Fig 11 OpAmp iLab oscilloscope interface As an aim of this work was to make the remote lab experience imitate a local laboratory as much as possible the lab client computer has embedded in it a help section which provides the students with relevant materials like datasheet for the LM741 IC resistor colour coding and information relevant to the circuit and SUT These go a long way in helping students to learn how to use datasheets and identify resistors using their colour code This way students who use this iLab are no less informed than those who work with the real devices V Evaluation and Discussion Evaluation of the pedagogical value and hence the effectiveness of the realistic in
18. terface was carried out on the basis that if our hypothesis on the extra benefit of realistic interfaces was correct then students should be able to handle real systems better with the new interface than with a schematic interface Hence in order to measure the effectiveness of the new interface students were given breadboards on which to connect op amp circuits using the LM741 IC and two resistors Two sets of students were used one set that had used the new interface to perform experiments and a second set that were only conversant with the op amp circuit schematics Our findings are presented in table 2 The results table 2 show overwhelmingly that having performed the OpAmp iLab experiment served as a major plus to a student being able to connect the real circuit manually Those who had only interacted with circuit symbols and had not interacted with realistic looking interfaces took much longer to familiarize themselves with the real components and understand how to make the connections Table 2 Evaluation Pedagogical Value of Improved OpAmp iLab Evaluation Criterion Students who used Students who did not use Standard deviation of the time for 2 minutes 6 seconds 4 minutes 55 seconds fomeimottwont nf Percentage who could use 100 60 ps Percentage who did not need the 20 LM741 datasheet to make their connections Percentage who could use a 100 60 fees a Percentage who connected the 60 0 A point to note from magni
19. tional Conference on Engineering Education Valencia Spain NI Educational Laboratory Virtual Instrumentation Suite NI ELVIS Hardware User Manual National Instruments August 2008 D Blazakis Interpreter exploitation Pointer Inference and JIT spraying In Blackhat USA 2010 Nedic Z Machotka J and Nafalski A 2003 Remote laboratories versus virtual and real laboratories In Proceedings of the 2003 33rd Annual Frontiers in Education Conference Boulder CO T3E 1 T3E 6 Kehinde L O 1989 The Dozen Impedance Operational Amplifier Module for Experimentation International Journal of Electrical Engineering Education vol 26 No 3 1989 pp 224 232 ManchesterUP Makoju G A E Nigeria Education Sector Diagnosis A framework for Re engineering the Education Sector Education Sector Analysis Unit Federal Ministry of Education Nigeria 2005
20. tude the standard deviation of the time for connection of the circuit table 2 is that some of the students who had performed the experiment using the improved OpAmp iLab knew what to do except how to do 1t They still had to spend a little time to familiarize themselves with the real equipment as opposed to the rich internet interface even though both of these were similar The time they took to familiarize themselves however was much shorter than those who had not interacted with the improved OpAmp iLab This suggests that while being much better than the conventional symbol based online laboratory client the realistic interface cannot completely replace the real life experience with the physical components at least not for all students A more elaborate study is on going to more elaborately assess the pedagogical value of the realistic interface Also we did compare the LabVIEW dll approach for signal processing used in the improved OpAmp iLab with the previous NI DAQ mx approach in terms of range of frequencies they can process This new approach made it possible to process a much wider range of frequency as it has a frequency span of 249 995 kHz as compared to the 0 016 kHz span of the previous implementation Figs 12a and 12b shows the result of the experiment when signals of frequency 0 2 kHz and 70 kHz were processed respectively Agiteat Technologies 0503202A 200 MHz WOTA STORAGE OSCH OSCOFE Fig 12 showing the sig
21. ver the internet using web services It consists of the NI SCI Chassis 1000 NI SCXI 1169 an LFH200 cable and NI TBX DB 50 The NI SCI chassis houses the NI SCXI 1169 100 SPST switch which is controlled by a Microsoft net web service The switches are controlled based on the arguments of a method contained in the switching matrix web service implemented with Microsoft NET C An LFH 200 cable was connected to the NI SCXI 1169 switch matrix to route the signals to the circuit NI TBX DB 50 was used between the 1169 and the circuit to help identify the switches and also to make the circuit a lot neater since a DB 25 connector which 1s connected to the switches on the circuit can be plugged into the TBX 50 IV Using the Interface in a Typical Experimentation Session To carry out experiments on the OpAmp iLab a student must log into the Service Broker If the student does not already have an account one must be created Once the OpAmp iLab client is launched most of the student s laboratory activities would be carried out on one of three screens the function generator screen the breadboard screen or the oscilloscope screen The sequence of a student s activities during a typical experiment session is depicted by a flow chart in Fig 7 Start select function generator screen select breadboard screen configure function generator Set Input Vin waveform type amplitude and frequency and confirm connect circuit verify circuit
22. y experience where students interact not with schematics but with the real components As mentioned one of the objectives was to provide students with flexibility in the choice of nodes on the breadboard to utilize in completing a connection To deal with this complexity the Depth First search DFS algorithm was employed to search through the connection matrix and determine if a start node root node is ultimately connected to another node goal node In the DFS implementation algorithm DFS was used to search through an array of points that have been connected Since DFS is used to search a tree structure the array created on connecting one node to another is first converted into nodes which are then used in the search The method for searching the tree structure takes two arguments the two arguments of the method are objects of the node class and they specify the two nodes we want to determine their connectivity The System under Test The SUT represented by the interface is a reconfigurable operation amplifier circuit as shown in Fig 4 It is capable depending on switches closed opened of implementing four different operational amplifier circuits mounted on the NI ELVIS experimentation board Table 1 shows position of switches for the four experiments The student never sees an actual switch depicted on the interface Instead by dragging across two breadboard holes of interest the student can connect two nodes Once the all nod
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