Introduction
Circuit design courses form a fundamental component of almost all engineering programs around the world. Traditionally, students learn the theoretical concepts of circuits from textbooks and use some form of simulation software such as Electronics Workbench Multisim to simulate circuits. However, in a majority of the classes, the hands-on aspect ended at simulation because students were forced learn and use a completely different set of tools, implement the circuit from scratch on actual hardware. Though prototyping in hardware allows students to compare theoretical and simulation results to real-world measurements and is considered extremely valuable in teaching circuit design concepts, the disjointed toolchain from software to hardware as shown in figure 1 has presented difficulties in facilitating a viable implementation for classrooms. Until now.
Bridging the Gap Between Theory and Real-World
Professors have sought tools that help bridge the gap shown in figure 1 between simulation and prototyping because they present an opportunity to vastly enhance student’s knowledge, better preparing them for industry, where engineers prototype and deploy circuits. Through improved use of hands on learning, students electronic assembly will gain a more complete understanding of the intricacies, and fundamentals of circuits. Circuits classes predominantly focus on the design, simulation and prototyping of circuits and throughout this paper, we will explore improvements in these three areas.
In order to bridge this gap between simulation and prototyping as shown in figure 2, there is a need for a single toolchain that enables students to design and simulate circuits and provide real-world I/O integration that will help students to prototype their circuits and test them with real-world signals. Hence, the toolchain should offer professors and students the capability to simulate any circuit they design and a platform that enables them to take advantage of these design and prototype them in order to measure the actual characteristics and finally, being able to compare the performance of the actual circuits to the simulated ones.
Integrated Circuits Teaching Platform
Fortunately, with the introduction of graphical design tools such as Electronics Workbench Multisim 9 and National Instruments LabVIEW and with prototyping platforms such as NI Educational Laboratory Virtual Instrumentation Suite (ELVIS) that are equipped with an integrated suite of instruments commonly used in a laboratory, there exists such a single toolchain that provides professors and students with an integrated circuits teaching platform. With the tight integration that exists between Multisim, NI ELVIS and NI LabVIEW, it is now possible to realize a seamless platform as shown in figure 3 that enables professors and students to design and simulate their circuits in Multisim, prototype the same circuit on NI ELVIS and finally compare the simulated and prototyped circuits in NI LabVIEW.
Case Study: Resistor Network Analysis
In order to illustrate this seamless toolchain, let us use a fundamental construct in circuit design, a resistor network. We will simulate, prototype and analyze its characteristics using a single platform. At each stage of the process we will identify the key features of the tools used and explain how they seamlessly blend together.
Theory – Analysis of the Resistor Network by Hand
Figure 4a shows the resistor network of interest. The problem at hand involves determining the voltages at nodes A and B. First, let us analyze this circuit by hand as shown in figure 4b.
Schematic Capture and Simulation using Multisim
Electronics Workbench’s Multisim provides an intuitive environment for placing electrical components and wiring them together into a schematic. The circuit schematic capture tool in Multisim is built around a sophisticated industry standard SPICE simulator. Multisim provides built-in instruments which can be connected to schematic circuits in the same way they would connect to a real-world circuit. SPICE was developed at the University of California, Berkeley, and stands for “Simulation Program with Integrated Circuit Emphasis”.
Circuits are created in the Circuit Window by placing components from the Component Toolbar. Clicking on the component toolbar will open the component browser. Users can choose the family of components, and select an individual component to place on the circuit window by double-clicking on it. Once a component has been selected, it will attach itself and “ghost” the mouse cursor. Clicking again on the desired location in the schematic will place the component. New users to Multisim should use the BASIC_VIRTUAL family of components, which can be assigned any arbitrary value.
Once the components are placed, the next step is to wire components together. Wiring is simple and can be achieved by a left-click on the source terminal, and then a left-click on the destination terminal. Multisim will automatically choose the best path for the virtual wire between the two terminals. Note that figure 5 shows the resistor network from figure 4 laid out in Multisim and wired together. Notice that the power source for this circuit is from an NI ELVIS schematic. This is one of the ways in which Multisim integrates with NI ELVIS.
With the NI ELVIS Schematic, students have access to exactly the same pins that exist on a standard NI ELVIS prototyping board. Hence, students can now use the function generator or the DMM from NI ELVIS in Multisim to virtually source and measure signals. Students may also choose the traditional schematic in which case they will not have access to these features.
Virtual Prototyping using 3D Virtual NI ELVIS
Once the schematic has been simulated in Multisim, and the results are satisfactory, a prototype can be built. Since Multisim is tightly integrated with NI ELVIS and LabVIEW, students now have the opportunity to use 3D Virtual NI ELVIS to virtually prototype their circuit as shown in figure 6.
The 3D Virtual ELVIS feature in Multisim provides several advantages for students learning circuit design concepts. Since it is virtual, students do not need to have hardware and can experiment with different layouts at their home or dorm. In addition, it helps students try different circuit layouts to find the most efficient one for their circuit. Multisim provides visual feedback on whether all the components have been placed and connected correctly by turning the symbols green on the schematic. Note that if a traditional schematic is chosen, a standard 3D breadboard will be available.
Prototyping and Testing using NI ELVIS Platform
Once the layout of your circuit has been verified using the 3D virtual environment it can be built on the NI ELVIS.
NI ELVIS consists of LabVIEW virtual instruments, a multifunction data acquisition (DAQ) device, and a bench-top workstation. The combination of LabVIEW virtual instruments, a DAQ board, and prototyping workstation provides all the functionality most commonly used in laboratories worldwide in a low-cost, laboratory-friendly form-factor. Professors and students can build customized instruments to suit their application using LabVIEW. Figure 6 shows the components that make the NI ELVIS. The workstation can be customized by using different experiment boards, such as a QuanserR controls board or a FreescaleR MPU board, or in this case a solder-less breadboard.
shows the actual resistor network as wired on the NI ELVIS. Observe that the source of the variable power supply is connected to the input of the resistor network. Similarly, the circuit is referenced to the ground line of the power supply. Notice that similar to the variable power supply, connections to the other instruments such as the oscilloscope, DMM, fixed DC power supply, AM, and FM modulator lines are also available on the breadboard.
Once this circuit has been wired, \the variable power supply provided by NI ELVIS can be used to provide 12 volts (V1) as needed by the experimental circuit and measure the nodal voltages using interactive graphical software.
Verification with Real-world Signals and LabVIEW
shows a screenshot of SignalExpress, an interactive measurement tool based on LabVIEW. SignalExpress provides a step-by-step interface allowing you to perform measurements. For this circuit, the first step is to provide the 12 volts supply which can be achieved by “inserting” a step in SignalExpress
Now a probe is connected to the DMM on NI ELVIS to measure the voltage at Node A. To see the measurement, a DMM step is inserted into SignalExpress. This voltage can now be displayed on the computer, exported to an Excel file or saved for later reference.
The most important step in the laboratory procedure is to compare measurements of the actual circuit to simulations. This will help you determine where potential errors exist in your design. For example, comparisons can help reveal inadequacies in simulation models, or incorrect components values.
After comparison with the theoretical values, you can revisit your design to improve it and prepare it for deployment. When your design is complete, you can use PCB layout software such as Ultiboard to create a PCB Assembly .
