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. Tektronix TBS1052 Two-Channel Digital Storage Oscilloscope
2. Tenma 72-8695A DC Regulated Power Supply
3. |Rigol DG800 Dual Channel Function Generator
4. 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.

The labs in this course occur at a more rapid pace than most, and there will be many instances when you will learn things in the lab that will be helpful to keep track of for future reference (e.g. how to solve problems, what settings to use, etc.)  To that end, we will be focused on keeping a functional lab notebook that can be referenced as needed throughout the quarter.  Your notebook should typically include:

• sketches of circuit diagrams
• component values used
• predictions about the functionality of a circuit
• notes on measurements taken
• a quick summary of observations made, deviations from expectation, problems encountered

Copies or scans of your work will be handed in at the end of each lab period to be graded by your TA.

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.

The breadboard used 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 the box at your station to connect the meter to the breadboard. 

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 to bring power and ground close to your components. You will be using the connections on the breadboard to build your circuits in the remaining laboratory sessions, so be sure to indicate the breadboard connections on the attached handout and include it in your notebook for future use.

The triple DC power supplies used in this lab (shown at right) 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.  To set a precise limit, you can short the terminals with a wire.  

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 one multimeter to measure this.  Leaving the first multimeter in place, connect the black terminal to the green one (ground) and use your 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). 

Use banana cables to connect the power supply to the breadboard.  Using jumper wires, establish horizontal bus strips (the long top rows, used to ‘bus’ signals long distances) on the breadboard for +3.0 V and 0.0 V.  

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 3.0 V?  Briefly explain. 

On your breadboard, build the circuit and check your prediction. 

Figure 1: A basic voltage divider circuit.  Note that the open white circles indicate points that are being measured across.

Use the function generator (shown at right) to create a sinusoidal signal with a frequency of 1 kHz and peak-to-peak (pk-pk) amplitude of 3.0 V.

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.

Using the handheld multimeter, try and measure the output signal.  You will need to select the AC voltage measurement mode ($\widetilde{V}$) 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 for a sine wave.  (We will discuss RMS values in more detail later in the course.)

Figure 2: An ac voltage division circuit.

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 TBS1102 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.

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.

Use a jumper wire to connect the probe tip to the non-grounded output voltage terminal.  The smaller ground lead (which has an alligator clip) should be connected to the grounded output voltage terminal. 

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.

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 $\rightarrow$ Top Softkey $\rightarrow$ Type=Pk-Pk. (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? 

Use two or three similar approaches in order to measure the frequency of the output voltage signal. 

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

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.

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?

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 $\rightarrow$ 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?

Note:  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.

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