Conducting Experiments Using the NI Electronics Education Platform

Publish Date: Aug 27, 2010 | 10 Ratings | 3.60 out of 5 |  PDF

Table of Contents

  1. The NI Electronics Education Platform
  2. Conducting an Experiment Using the NI Electronics Education Platform
  3. A Simple RC Laboratory Experiment
  4. Design Challenge and Theory
  5. Schematic Capture
  6. Simulation
  7. Virtual Breadboarding
  8. Prototyping, Measurement, and Comparison
  9. Conclusion

1. The NI Electronics Education Platform

The NI Electronics Education Platform is an integrated tool-chain designed to meet the needs of students and educators. This platform consists of an ideal mix of   hardware and software that guides students through the engineering and design process, from understanding circuit theory, to developing and simulating designs and onto prototyping and validation.

The platform consists of NI Multisim, NI ELVIS, NI LabVIEW and SignalExpress. NI Multisim provides professional caliber schematic capture and simulation software to help students explore circuit theories, and investigate behaviors through intuitive and interactive SPICE simulation. Multisim also includes a 3D prototyping environment which can help a student bridge the gap from a software environment to real-world design. The NI ELVIS is a breadboard prototyping platform that allows students to quickly and easily develop their circuits, and interactively take measurements using 12 built-in virtual instruments. NI LabVIEW and SignalExpress are ideal environments for students to interface to measurements, and compare their measurements to simulations within a single display.

 

Figure 1 - The NI Electronics Education Platform

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2. Conducting an Experiment Using the NI Electronics Education Platform

The purpose of a laboratory experiment is to familiarize students with the engineering process, and equip them with the tools of an engineer. The first step in the laboratory experience is to present a student with a design challenge. By utilizing their problem solving skills the student is required to propose a solution to the challenge, and develop that solution through theoretical and practical experiments.

A laboratory in electrical engineering is no different, and the NI Electronics Education Platform is an ideal environment for students to carry-out these laboratory experiments.

This article describes as an example, a typical student's laboratory. At each stage of the process, we use the software and hardware elements of the Electronics Education Platform. The diagram below lists the steps of this process.

 

Figure 2 - The Electrical Engineering Laboratory Flow

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3. A Simple RC Laboratory Experiment

A common first design challenge for an Electrical Engineering student, is to predict, develop, measure and analyze a simple RC filter circuit. The RC filter acts as a Low Pass Filter, by rejecting input signals which have a frequency above the cut-off frequency.

In this article we carry out the design of this RC filter using all of the tools in the NI Electronics Education Platform. We use NI Multisim to capture, simulate, and virtually prototype the RC circuit. Each part is split into a separate tutorial which can be used as a stand-alone project, or as part of a series of design challenges for a student. We then prototype the RC circuit on the NI ELVIS prototyping platform and use its built-in virtual instruments to measure various characteristics of the circuit. Finally we use NI SignalExpress to automatically measure and compare our results to the simulations provided by NI Multisim.

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4. Design Challenge and Theory

The design challenge is to design a low pass filter with a cutoff frequency (or -3dB point) of 159 Hz.

Given a simple RC series circuit for analysis, we can use Kirchoff's Current or Voltage Law to derive the expression for the Gain (Output voltage divided by input voltage).

 

The gain of this circuit is given by:

The fundamental frequency in Hertz, or half power for this circuit is given by:

With a cutoff frequency of 159 Hz, then 2 * pi * 159 = 1000 Hz. Which means that 1/RC = 1 / 1000. RC = 0.001

Let R = 1000 Ohms, then C = 1 uF.

 

Figure 3 - A Simple RC Circuit

Now with values of R and C selected, it's time to continue along the laboratory process. The following articles detail the capture, simulation, 3D prototyping, and NI ELVIS prototyping, measurement and comparison of the simple RC filter above.

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5. Schematic Capture

NI Multisim provides a default or blank schematic for capturing and simulating simple designs. However for those students that will use the NI ELVIS workstation in the laboratory, Multisim also provides an NI ELVIS template schematic, which includes all of the NI ELVIS breadboard connections including the oscilloscope , function generator, and among others the Multimeter terminals. For a more detailed description of the NI ELVIS workstation, see our article on the NI ELVIS .

Start by creating a new NI ELVIS schematic for circuit capture and design. From within Multisim click File >> New >> NI ELVIS Schematic. A new blank NI ELVIS template will appear.

 

Figure 4 - Blank NI ELVIS Template Schematic

The best way to place components for simple circuits is by using the Basic component toolbar. When one clicks on an icon in the basic component toolbar, the chosen component will attach to the mouse cursor. Then a second click will place the component onto the schematic.

If not already visible, access the Basic toolbar by clicking View >> Toolbars >> Basic.

Figure 5 - Basic Components Toolbar

Power source components such as ground, or VCC or VDD are available in the Power Source Components toolbar. In the diagram below, the ground component is circled.

Figure 6 - Power Source Components Toolbar

Using the Basic and Power Source Components toolbar, we will capture the low-pass RC Circuit. The diagram below shows the end result of the capture process. Following Figure 7 are a complete set of step-by-step instructions on how to capture this circuit. Because we are using the NI ELVIS template schematic, we are able to provide stimulus, and measure response from the schematic just as we will using the real NI ELVIS workstation.

Figure 7 - Completed RC Circuit in Multisim

Wire the RC Circuit

  1. Place a 1.00 kΩ resistor.
  2. Place a 1.0 µF capacitor
  3. Connect the FUNC_OUT pin to one of the terminals of the resistor. To draw a wire, left click on the source pin to begin the wire, and then left click on the destination pin to complete the wire.
  4. Connect the second pin of the resistor to either of the capacitor terminals.
  5. Connect the second capacitor terminal to ground.
  6. Select and double click the input net and rename it to “Stimulus” from the Net dialog box. Before closing the dialog box, check the “Show” box to have the net name displayed on the schematic.

Net Properties Dialog Box

Figure 8 - Net Dialog Box

  1. Select and double-click the output net and re-name it to “Response” in the Net dialog box. Before closing the Net dialog box, check the “Show” box to have the net name displayed on the schematic.

Wire the Oscilloscope

  1. Place a ground reference terminal near the Oscilloscope Channel B-.
  2. Connect Oscilloscope Channel A- and B- to the ground terminal that you just placed
  3. Begin a wire from Oscilloscope channel A+ and double-click on a blank area of the workspace to terminate the wire.
  4. Select the net placed in step 3, and rename it to “Stimulus”. This will virtually connect A+ to the stimulus net. Multisim will warn that a net with the same name already exists, and ask you to confirm that you want to virtually connect. Click Yes.
  5. Begin a wire from Oscilloscope channel B+ and double-click on a blank area of the workspace to terminate the wire.
  6. Rename the net to “Response”. This will virtually connect B+ to the response net. Multisim will warn that a net with the same name already exists, and ask you to confirm that you want to virtually connect. Click Yes.

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6. Simulation

Since we captured the circuit on the NI ELVIS template schematic, we can use its built-in virtual instruments to take time-domain measurements from this circuit. We will use the Oscilloscope to measure the transient response, which will give insight into the circuit behavior in the time domain.

In order to measure the frequency response of this circuit we will replace the function generator with a traditional AC source, and use the Multisim Bode Analyzer.

Transient or Time-Domain Analysis

Using the Oscilloscope we will be able to see the stimulus and response of the RC circuit as it simulates. This method of interactive simulation is especially useful when exploring new concepts in circuitry, as changes to the circuit can be immediately visualized.

To begin simulation, we use the simulation toolbar, which contains buttons that are most commonly used during a simulation. The simulation toolbar allows you to start, stop, and pause simulation. When performing Microcontroller (MCU) simulation, the simulation toolbar will also allow provide code debugging features such as stepping into and out of code and the insertion or removal of breakpoints. For more details on MCU simulation please see Microcontroller Unit Co-Simulation for SPICE-based Circuits.

Figure 9 - Simulation Toolbar

Note: Before we begin simulating, it is important to note that the color that traces will display on the oscilloscope (and other instruments) is the same as color as that of the wires leading into the terminals of the instrument. This means that in order to differentiate the traces on the oscilloscope, it is best to change the color of the traces.

1. Change the color of channel B’s trace to blue. 
        1.   Right click on the wire leading to Oscilloscope Channel B+ (Response) 
        2.   Select “Change Color” 
        3.   Choose a color that is easily differentiated from red such as blue. 

2. Begin simulation of the circuit 
        1. Click on the play button on the simulation toolbar

Note that the status bar at the bottom-right hand corner of the screen will indicate that simulation time is proceeding. This means that your circuit is now simulating.

3. Double-click on the NI ELVIS template symbol of the oscilloscope to open the front panel of the oscilloscope. 

Figure 10 - Virtual NI ELVIS Oscilloscope

The oscilloscope will open to reveal the results of simulation. You should see the default 5 Hz sine wave passing through the RC filter. At this slow input frequency, the output of the circuit will very closely match the input.

4. Adjust the oscilloscope settings to better view the transient simulation results. 
        1.   Adjust the volts / div for each channel to 1.

Figure 11 - Oscilloscope Front Panel

 5. Change the input function characteristics.
        1.   Stop the simulation by clicking on the stop button from the simulation toolbar
        2.   Open the Function Generator 
        3.   Change the frequency to 159 Hz. This is -3dB or cutoff frequency of the circuit.

6. Start the simulation

You should now see both input and output. The output is significantly attenuated at this point, and you should notice that the phase has shifted as well.

Note: You can switch the color of the background of the oscilloscope by selecting the reverse toolbar button from the oscilloscope front panel.

Figure 13 - Oscilloscope Showing Transient Response at Higher Frequencies

The transient data can be saved for later comparison with real measurements. In this tutorial, we compare the simulation of the frequency response to its measured counterpart.

AC or Frequency Domain Analysis

Now that the transient response of the circuit has been predicted, the next step is to measure the frequency response of the circuit. To do this, we connect a traditional AC stimulus and the bode analyzer to the circuit. The resulting schematic is shown below.

Figure 14 - Circuit for AC Analysis

1. Place an AC source, located in the Signal Voltages family of the Sources group of the Master Database.

Figure 15 - AC Source

2. Configure an run an AC Analysis. Click Simulate >> Analyses >> AC Analysis. Configure the Analysis configuration and output as shown below in Figures 16 and 17.

 

Figure 16 - AC Analysis Configuration Settings

Figure 17 - AC Analysis Output Settings

3. Click Simulate. The Grapher will open and display the results of the AC Analysis as shown below.

Figure 18 - Grapher Display - The Red Triangle Indicates the Active Graph

Note that the results of an AC response are in split into magnitude and phase. The units of the magnitude plot are volts, and the units for the phase plot are degrees. Typically in a lab setting we are interested in the Bode plot of the AC response. The Bode plot can be realized by adding a trace that displays the magnitude in terms of Decibels.

A decibel is a relative measurement of the output magnitude divided by in the input magnitude calculated as 20*log(Vout/Vin). Since the AC voltage input to the circuit is unity or 1, then simply performing 20*log(Vout) will give us the Bode magnitude response. Multisim allows a trace of any arbitrary expression to be added to the grapher. Using the built in function db(), we can easily see the results in terms of Decibels.

4. Add a trace to display the magnitude response in Decibels.
    1. Click the add trace button from the Grapher toolbar as circled below in Figure 19.

Figure 19 - Grapher Toolbar with Add Trace Circled in Red

    2. From the Add Trace dialog box, click the Add button.
    3. Double Click db() from the functions list-box.
    4. Double Click V(Response)
    5. Click Calculate.

Multisim will add the magnitude of the AC response in Decibels to the graph. Now we save the results to a text file for use later in comparisons between measured data and simulations.

5. Save the results. 
    1. Click File >> Save As.
    2. Select Text file (*.txt) from the Save as type section.
    3. Name the file "AC Response.txt". Multisim will save all 3 traces to the data file. We come back to this data later.

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7. Virtual Breadboarding

The next step in the process is to virtually prototype the RC circuit in a 3D environment. Virtually prototyping circuits allows students to familiarize themselves with the concepts of breadboarding, and provide a risk-free environment to experiment with different layouts, and determine the exact circuit layout before going to the laboratory.

What is Breadboard Prototyping?

Breadboarding is one of the most common methods of building simple and advanced circuits. A breadboard is a rectangular plastic board with hundreds of small metal-plated holes. Many of the holes are electrically connected internally, allowing you to place components on the board, yet still connect other components to them through the use of jumper wires.

 

 

Figure 20 - Breadboard Amplifier

 

Figure 21 -  3D Virtual Prototype

The diagram below highlights four groups of internally connected holes to illustrate the topology of the NI ELVIS breadboard. The connections marked 1 provide four holes that are electrically connected together, and to the analog channel 0 of the NI ELVIS data acquisition device. The areas marked 2 and 3 demonstrate that horizontally holes are internally connected in groups of five holes. For example, row 1 column A is connected to row 1 columns B, C, D, and E, but connected to none of the holes in columns F, G, H, I and J. The group of holes marked 4 illustrate that holes along the left and right sides of the breadboard are connected together. In the diagram below, the holes next to the red stripe of the left side are connected to one another, but are NOT connected to the holes next to the blue stripe.

Figure 22 - Sample Breadboard Internal Connections Highlighted

What is Virtual Prototyping with a 3D Breadboarding?

Virtual prototyping is a method for developing prototype circuits in a software simulation environment like Multisim. Virtual prototyping allows you capture your circuit using the intuitive Multisim environment, predict circuit behavior using SPICE simulation, and finally prototype your circuits on a 3D breadboard.

Why Breadboard in 3D?

Experiment Risk-Free

Students should use virtual prototyping using the 3D breadboard because it provides a risk free environment. Students can experiment with varying topologies without accidentally shorting circuits, or destroying instrumentation.

Save Time in the Lab

Virtual prototyping allows you to quickly build circuits in a simulated environment, and check your designs for errors. Multisim will inform you of any wiring errors including shorted wires, shorted and forgotten components, and even backward capacitors and diodes.

Learn at Home

You don’t need to have a full laboratory workstation in order to prototype in a 3D environment. You don’t need to schedule lab-time at school, and can build-up your prototypes on your own time at home.

Understand Circuits Better – Avoid the Rat’s Nest

3D prototyping will force you to develop better wiring techniques and avoid those difficult to follow “rat’s nests”. A “rat’s nest” is a nick-name for a poorly wired breadboard circuit.

Virtually Prototype the RC Circuit

We now prototype the circuit from Figure 7 (shown again below).

Figure 23 - Completed Circuit for Virtual Prototyping

1. Open the 3D Breadboard View. Click Tools >> Show Breadboard.

Notice that the main toolbar will change to reflect the new breadboard view. The diagram and table below list the new buttons available in this view.

Figure 24 - Main Toolbar in the 3D Environment

Toolbar Button

Function

1

Change wire color

2

Rotate breadboard 180 degrees

3

Change breadboard settings

4

Show current breadboard netlist

5

Perform design rule and connectivity check
 
The NI ELVIS 3D Breadboard will appear. You can use the mouse to rotate the view, place components, and connect wires. The mouse cursor will change to reflect whatever operation will be performed.
 
 Rotating the display  Click and drag on a blank area of the breadboard.
 Placing components  Click and drag components from the component bin at the bottom.
 Connecting Wires  Click on a source hole, and then click on a destination hole.

To place components onto the breadboard, click and drag them from the component bin at the bottom of the display. Using this method, place all of the components in your circuit.

Multisim will automatically detect this, and consider those pins to be connected. By placing two components pins on the same bus, you can connect them electrically.

2. Connect the resistor and capacitor as shown. Notice that the pins of the resistor (as in the lab) are reversible. Resistors in the 3D view are not polarized. Use Ctrl-R to rotate the component.

3. For any nets that were not made internally simply by choosing appropriate component locations, you can connect them externally by placing jumper wires. Left click on an empty hole to begin a wire, and then left click again on an empty destination hole to create a wired connection between those two holes.

Multisim will help you to decide to where a particular wire should be connected. When you click on an empty hole to begin placing a wire, the 3D environment will highlight all of the holes that should be on the same net of the wire you are placing. This concept is best described with the illustration included below.

Where appropriate, try to use a color code to help others to visually inspect the circuit.

The completed circuit should look similar to the image below.

Figure 25 - Completed 3D Prototype

4. Once all of the components are placed, and all nets have been wired, run the design and electrical rules check. Click on the DRC button from the main toolbar, and Multisim will list wiring errors.

5. The last step in this process is to verify that all the placed components and nets turn green. This is a visual method for checking the design.

Figure 26 - Schematic After Feedback from the 3D Environment

The 3D prototype is complete. 

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8. Prototyping, Measurement, and Comparison

The final stage in the electrical engineering laboratory is to physically prototype the circuit, measure the behavior and characteristics of the circuit, and then compare those measurements to simulations.

The figure below illustrates the completed prototype on the NI ELVIS workstation.

Figure 27 - Completed NI ELVIS Prototype

Transient Response Measurement

Using the NI ELVIS Instrument launcher, we measure the transient response of this circuit. We leave the comparison
of transient results as an exercise for the reader.

1. Ensure the NI ELVIS workstation is powered and connected to the PC (via USB, PCI, or PCMCIA bus).
    For direction on configuring the NI ELVIS please see Where to Start with the NI ELVIS.

2. Configure the function generator.
    1. Set the function generator to Manual mode, this will allow user control of the amplitude and frequency settings.
        For a frequency response as covered by the next section we will switch the NI ELVIS function
        generator to automatic.
    2. Set the coarse frequency range to 500 Hz.
    3. Set the fine frequency range to around 50% of a full turn of the knob.

3. Run the NI ELVIS instrument launcher (Start >> Programs >> National Instruments >> NI ELVIS >> NI ELVIS).

4. Open the Oscilloscope. Configure the Oscilloscope as shown in the illustration below.
    1. Set the trigger to SYNC_OUT.
    2. Turn on Channel B.
    3. Set channels A and B to 500 mV per division.
    4. Set the timebase to 1ms.

5. Using the function generator controls on the front of the NI ELVIS, set the input voltage to 1 Vp-p, and the input
    frequency to 159 Hz. Note the p-p measurement of Channel B. This measurement can be used to determine the
    difference between simulation and real measurement. However, we use the NI ELVIS Bode Analyzer to get a better
    picture of the frequency response of the circuit.

Frequency Response Measurement

Using NI SignalExpress, we measure the frequency response of the circuit. The SignalExpress environment is a non programming software tool based on NI LabVIEW which enables quick and easy measurements. By placing simple steps, the NI ELVIS Bode Analyzer can automatically perform a frequency sweep measurement and return the frequency response of the RC circuit. Likewise a similar step to load the simulation results saved from Multisim.

We will open SignalExpress and place two steps: one to capture a bode plot from the NI ELVIS Bode Analyzer, and one to load our simulation results.

Note: Before we start, ensure that the function generator "Manual" switch on the NI ELVIS is set in the down position. This will allow SignalExpress to programmatically control the function.

1. Click Add Step >> NI ELVIS >> Analog >> Acquire Signals >> NI ELVIS Bode Analyzer. Configure the step as shown below.

Figure 28 - NI ELVIS Bode Response

2. Place a SignalExpress step to load the simulation results from Multisim. Click Add Step >> Load/Save Signals >> Load from SPICE. Configure the step as shown below.

Figure 29 - Load from SPICE

3. Click Run Once to begin the measurement.

SignalExpress will automatically control the NI ELVIS function generator to perform a frequency sweep between 10 Hz and 1000 Hz.

4. Once the sweep has completed, we place the simulated magnitude and measured magnitude data onto the top plot. To do this, click and drag the Gain Data and then db(V(Response) onto the data-view on the right-hand side.

5. Add a display below the magnitude plot. Right-click on the magnitude plot on the right and choose add-display, then choose below.

6. Drag the Phase Data and V(Response) to the bottom display on the right-hand side.

The SignalExpress display should now be showing both magnitude and phase simulations, as well as the measured NI ELVIS data. The display should look like the illustration below.

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9. Conclusion

By using the integrated tools of the NI Electronics Education Platform students can complete the design process of electrical engineering undergraduate laboratories.

NI Multisim provides an intuitive and capture and simulation environment which encourages students to explore circuit behavior, play "what-if" scenarios, and save their simulation results for use further in the process.

Once designs have been realized in NI Multisim, the NI ELVIS provides built-in instruments that can easily be controlled to measure and understand real-life circuit behavior.

Lastly, SignalExpress allows for a simple and quick comparison between measurements and simulations.

To learn more about the NI Electronics Education platform, see ni.com/academic/circuits.

 

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