Goals


In the first lab, you will become acquainted with a set of standard tools that are used for building and testing electronic circuits.  These include:

  1. Electronics breadboard (or protoboard)

In addition, you will be using a variety of test leads and coaxial cables to make connections between test devices and the circuit you are working on.

Electronics vs Physics Labs

In most of the instructional lab courses on physics, the focus has (broadly) been using evidence to make conclusions about physical systems. The electronics course has a different goal: for you to learn enough about circuit design and functionality to start to be able to understand and design circuits in service of doing experimental physics. As such, the structure of the course will be markedly different that what you've seen before.

  • Labs are numerous and hands-on Due to the overhead needed to get to building functional circuits, there will be 16 lab periods throughout the quarter. The first labs in particular will have more guided exercises to help you get a solid foundation in circuit behavior and how to use the test & measurement equipment.
  • Lab writups will be minimal As the focus is on building, testing, and designing circuits, you aren't expected to write extensive reports. What you are asked to submit is a short document typically covering key observations.
  • Uncertainty analysis has no place here While it is certainly possible to perform uncertainty analysis on circuit behavior, it is unlikely to be helpful for this course. The issues you encounter are usually either enormous (improper connections or incorrect components for example) or very subtle (capacitive behavior in diodes or bandwidth limitations on test instruments) that they are unlikely to be explained by analyzing uncertainties.
  • Failure is always an option It will not be uncommon to observe a circuit malfunction because you haven't built it correctly, or because you've made mistakes (or unwarranted assumptions) involving the test & measurement equipment. This still happens to experienced designers, and as you get more experienced you'll be able to troubleshoot problems more quickly.
Pros at work

  • Troubleshooting is an integral part of design Since things may not work the first time, you'll have to figure out both why they aren't behaving as expected and how to fix them. Some general guidelines can be found here.
    • Before you ask your TA for help, you should be able to provide some more specific information than “It isn't working.”
  • Predictions are important As a corollary to the previous point, you need to know what a circuit is supposed to do to figure out if it isn't doing it. Sometimes you can make very specific predictions (e.g. “The amplitude should be cut in half when we increase the frequency to 39 kHz”) and other times you might have broader predictions (e.g. “I should see the voltage change when I turn on the function generator”), and when you're really struggling to figure out things you might fall back to extremely basic things (e.g. “It should behave differently when I turn the power off” or “touching a resistor shouldn't do anything”).

Lab Submission

For each lab, a template containing guiding questions will be provided to you.  You should also keep a lab notebook as a way of recording what you do and why, but it will not be assessed by your TA.

Questions may appear in the webpage that are not reflected in the template.  You don't have to document anything related to said questions, but they are there to guide you in thinking about electronics in a more expert fashion.  The hope is by the end of the course you'll start asking yourself such guiding questions without prompting, but until then such questions will provide you with support.

On Wiki Formatting

Since a good portion of this lab will feature guided activities, we've set up a system to help differentiate information from instructions from rhetorical questions. Information and general background has no special formatting

Rounded grey boxes are used to denote instructions: What you need to physically do as you proceed through the lab.

Text that's offset like this is used to indicate points to test or consider. Not all such instructions need to be recorded in your report, but you should be able to answer them as you go through the lab. They will help you gauge how much you're absorbing the content of the class.
Sometimes there are clickable notes in bold text

These notes typically:

  • Instructions on how to do something specific that not everyone will need,
  • Longer derivations of mathematical terms for the curious, or
  • Bits of supplementary information/trivia/history that aren't strictly necessary.

Some electronics jargon will have clickable or hoverable links to explain new terms more fully

Exploring the basic setup


Throughout the semester, we will be wiring circuits on a standard electronics breadboard or protoboard.  In addition, we will typically be using the regulated power supply to provide a DC voltage for our circuits. In this section, you will use the digital multimeter (or DMM) to investigate the breadboard and the power supply.

Your digital multimeter, with minigrabber leads. You will need to turn the knob to the yellow $\Omega$ symbol to measure resistance.

Exploring the breadboard.  

A breadboard like the one we'll use in this course is shown below.  Explore the interconnections between various points on the breadboard using your DMM in resistance mode (Ω).  A low reading shows an electrical connection while a very large reading or overload (OL) message indicates that there is no connection.  Note that the leads on the DMM do not fit into the breadboard holes; you will need to use jumper wires from your kit to connect the meter to the breadboard. 

Using your multimeter, explore the connectivity of the breadboard. You'll be using it throughout the entire course, so taking some time now to really understand its layout can help save you time later when you're building circuits.

Make sure that you understand how the contact points are connected, paying particular attention to the vertical running holes on the sides of each board segment and to the horizontal running holes at the top of the board. These points are often used as a

power bus

Bus

A Bus is something used to transmit signals or powering voltages over long distances. In this class we'll use the later definition more frequently, as often we'll want to connect multiple components to the same voltage (commonly +5V or 0V) without turning everything into a mess of wires.

2022/03/22 13:27 · kevinv

to bring power and ground close to your components.  The report template has an editable breadboard schematic for you to annotate.

A photo of the breadboard you have for this course.  Note that this has six identical modules on the lower portion. A schematic of the breadboard.  Click on the image for a larger version to annotate or download.

Exploring the power supply

The triple DC power supplies used in this lab (shown below) can each produce two independent variable DC voltages (with maximum voltage and maximum current settings) as well as a constant 5 V output. When using the variable supplies, they will typically be used as constant voltage sources and the currents drawn will usually be on the order of mA. Given that the supplies are capable of supplying 3 A of current, it is a good idea to set the current limit to approximately 0.5 A (1/6 of the total current range) or less; you can do this by turning the current knob fully counter-clockwise and then adjusting it clockwise by about 3 or 4 small gradations.

Our benchtop power supplies. Note that the knobs and indicator lights are mirrored from left to right channels.
What if I want more precision?

To set a precise limit, you can short the terminals with a wire while adjusting the current limit knob. Note that this is a terrible idea if you are working with an unknown device! Always check the manual unless you are keen on voiding warranties or starting fires.

It is important to note that the power supply is floating supply; a setting of 5 V only tells us that the potential difference between the two supply terminals is 5 V. It says nothing about how either potential compares to ground (0 V). In order to set one of the terminals to ground, you must connect that terminal (and that terminal alone) to ground (green GND label) using a banana cable or some other type of connector.

Configure your power supply such that there is a 3 V difference between the red and black terminals, and set up a multimeter to measure this. Leaving the first multimeter in place, connect the black terminal to the green one (ground) and use a second multimeter to measure the differences between ground and the other two terminals. Then, connect the red terminal to ground and repeat.

Did the connection to ground change the potential difference between the terminals?

Configure your power supply such that the + terminal is set to +3.0 V and the – terminal is grounded (0.0 V). Connect it to the terminals at the top of your breadboard, and wire those to two different horizontal bus strips (the long top rows, used to ‘bus’ signals long distances) on the breadboard.

To connect the power supply to the breadboard, unscrew one of the banana jack connectors at the top of the board. When re-tightening the connector, make sure that only exposed metal is in the hole. Don't tighten the connector on the insulation; even if it works some of the time it will cause intermittent problems.

Your first circuit


During the first few weeks of the course, we will cover voltage divider circuits extensively.  In this lab, we are asking you to build a simple voltage divider circuit to gain experience with assembling circuits on the breadboard.  Consider the circuit shown in Fig. 1.

Predict whether the absolute value of $V_{out}$ will be greater than, less than, or equal to the voltage of the power supply, +3 V.  Write your prediction in your report, and briefly explain. 

On Predictions

Making predictions is more important when working with electronics than typical labs.  You can't see what's happening in circuits directly, so if you don't have some expectations for how something should behave it is hard to tell if it is doing what it is supposed to or if there is a problem.  Sometimes predictions can be as simple as “If I disconnect the input I should see 0V at the output,” or “If I wiggle a cable nothing should change.”  These basic low-level predictions are at the heart of troubleshooting circuits, which you will inevitably need to do during this course.

Figure 1: A basic voltage divider circuit.
The circuit shown in a traditional format from PHYS 132/142 courses. Note that the open white circles indicate points that are being measured across. The same circuit depicted in a compact notation. $V_{out}$ is still measured with respect to ground, and the more negative terminal of the power supply is also connected to ground.

Breadboarding example

Four examples of the same circuit. All are topologically identical, but the building style on the right (utilizing the power rails, laying out parts along clear & straight lines, etc.) is preferable for working on larger projects.

Connecting to the voltage divider circuit.

Keep your power supply connected to the breadboard for now.

On the bottom part of your breadboard, build the circuit and check your prediction.

Be sure to record what you measured and reconcile your observations with your prediction.

Adjust the voltage of your power supply throughout the range of values available to you, and observe the effect on the circuit's output $V_{out}$

Does the voltage divider behave the same way as the voltage varies?

Generating waveforms


More often than not, function generators are used to create waveforms with known properties so that we can observe the effects our circuits have when given particular inputs.  Let's try and do that now. You'll use the control panel to set the shape, frequency, and amplitude of a sine wave.  

Using the handheld multimeter, try and measure the output signal from your function generator.  You will need to select the AC voltage measurement mode $\tilde V $ on the multimeter.  Note that the reading does not correspond to the signal’s amplitude but rather its root mean square (RMS) value, which is about .7 times the amplitude (or .35 times the peak-to-peak amplitude) for a sine wave.  (We will discuss RMS values in more detail later in the course.)

Experiment with the settings on the function generator, such as the frequency, amplitude, offset, and/or waveform.  What changes is the meter sensitive to?

Reset the function generator (shown below) to create a sinusoidal signal with a frequency of 1 kHz and peak-to-peak (pk-pk) amplitude of 3.0 V. This is the default setting, so if you aren't sure how to do this you can turn it off and on again.

Applying a sinusoidal input voltage to the voltage divider circuit

Use a BNC-to-paired-banana-plug adapter and two banana cables to connect the Channel 1 output from the function generator to the voltage divider, replacing the DC power supply as shown in Fig. 2.

The BNC connector should slide in gently, and lock when it rotated when it is turned about a quarter of a turn clockwise. The outer conductor of the BNC cable is grounded, and you will need to ensure that the grounded (black) lead from the function generator is connected to the grounded output terminal in the circuit.

Figure 2: An AC voltage divider

Sidetrack: A Review of Oscilloscopes


The oscilloscope is by far your most versatile tool.  It is a graphing voltmeter, displaying voltage as a function of time.  Your scope, a Tektronix TDS1052 digital storage oscilloscope (shown at right), has two channels and thus is capable of showing the temporal behavior of two different signals.  In this section, you will use the scope with a standard 10X probe in order to examine the behavior of the output voltage from the voltage divider circuit. Start your scope by pushing the power button on the top of the scope.  It will take a few seconds for the scope to start up; once startup is complete, press one of the rectangular “softkey” buttons to the right of the screen.

Introductory video for Tektronix Oscilloscopes

Measuring signals with the 10X probe.

Your 10X scope probe attenuates the measured voltage signal to 1/10th of its size.  Thus the signal must be digitally multiplied by a factor of 10 (10X) in order to accurately display the measured voltage at the tip of the probe.  The scope is configured to do so normally, and for this course the 10X probe is suitable for routine measurements.

Why would we do this?

The 10x probe has a compensating capacitor that lets it accurately display signals on a much quicker time scale than would be possible just using wires.  If we were to use only a regular coaxial cable, then we would start to see distortions on a time scale of 10s of nanoseconds; this is enough to distort many digital signals. 

Use a jumper wire to connect the probe tip to the non-grounded output voltage terminal of your circuit, in place of one of your multimeter connections.  The smaller ground lead (which has an alligator clip) should be connected to the grounded output voltage terminal. 

A 10x probe, ready to be used to measure signals.

When measuring signals with the scope, it is often helpful to first use the AutoSet key to obtain a stable scope trace.  (Note:  AutoSet can be problematic in certain cases, such as when viewing non-periodic signals.) 

Press AutoSet now and observe the result.

Is it what you’d expect?

Examine the impact of changing:

(1) the Volts/Division by adjusting the vertical scale for Channel 1,
(2) the Seconds/Division by adjusting the horizontal scale,
(3) the vertical position of the trace, and
(4) the horizontal position of the trace.  See handout below.
An image that depicts the controls on your oscilloscope. An editable copy is embedded in the lab template.

Measure the peak-to-peak amplitude of the output voltage signal three different ways: 

(1) Measure directly from peak to peak using only the grid and vertical scale information on the scope, adjusting the position of the trace for ease of measuring;

(2) Use amplitude cursors by selecting Cursor $\rightarrow$ Type=Amplitude $\rightarrow$ Source=CH1 and then adjusting cursors 1 and 2 as needed via the multipurpose knob (top left); and

(3) Make an automatic measurement by selecting Measure $\rightarrow$ Second Softkey $\rightarrow$ Type=Peak-Peak. (Note: This may be accomplished either by pushing the softkey to cycle through the measurement types, or by turning the multipurpose knob after the initial softkey selection.)

How similar are your measurements? 

How well do these measurements agree with one another and with the amplitude setting on the function generator?

Limitations of the oscilloscope


Like all measurement tools, the oscilloscope has limits to the precision of its measurements, and the calculated values in particular may behave unexpectedly in certain instances.  Start by setting the scope to measure both peak-to-peak voltage (which it should be doing already) and frequency.

Without changing any settings on the oscilloscope, decrease the frequency setting on the function generator until the measured frequency indicates a question mark. 

What do you notice about the signal? 

Now adjust the settings on the oscilloscope until the values once again agree. 

In what way has the image on the screen changed?  Repeat the same procedure for the amplitude of the signal, and then summarize what is required for the automatic measurements to be accurate.

Measuring small signals. 

Decrease the amplitude of your input to 300 mV on the function generator, and adjust the scope until you can once again see the output signal.  How has it qualitatively changed?  Is the peak-to-peak measurement still accurate?

Now, use the Acquire  $\rightarrow$ Averaging Softkey to make the oscilloscope display an average of several wave cycles at a time. 

How does this affect the peak-to-peak measurements?

Remember to turn averaging off before proceeding!

Signal Triggering

Many people consider triggering (the process whereby the scope starts the signal display) to be complicated.  While the importance of triggering will become more apparent in future labs, the following short exercises should help clarify the triggering process. 

Your scope defaults to edge triggering.  Using an input sinusoidal voltage signal with a peak-to-peak amplitude of 3 V, use the scope to measure the output voltage signal from the circuit.  Adjust the Level knob at the top of the trigger controls. 

What happens to the scope trace? 

Access the Trig Menu → Slope and explore the impact of triggering on the rising or falling edge of the signal. 

Practice using the level knob and slope controls to make the trace start wherever you choose.  The scope is triggering correctly if “Trig’d” appears in green text at the top of the screen.

Can you make it start at the top of a sine wave?  Can you make it start at the negative half of the wave?

Use the Trigger Menu to switch the Mode from Auto to Normal. 

What happens when you adjust the Level settings in Normal mode?

Further details about triggering can be found in the User Manual.  Over the course of the semester, we strongly suggest that you become familiar with standard techniques for measuring amplitudes, periods and frequencies, rise times, and phase shifts.

Assignments are due 48 hours after the end of lab

This page is adapted from “Flexible Resources for Analog Electronics” by Stetzer and Van De Bogart