PHY 405: Electronics Lab Lab # 1

Lab # 1: Measurement basics

Throughout this course, you may find it useful to roughly plot data in your note-book/computers as soon as you make measurements. Plotting your data as soon as youacquire it will help you to understand what you are doing better, and to quickly identifyif there are any problems. You can produce higher quality plots for your reports at alater time.

Remember: You are required to turn in lab reports (according to the specificationslisted on the course webpage), not your lab notebooks.

Background preparation

• Oscilloscope (“scope”) basics: introductions posted on the course webpage.

• Voltage sources, Thevenin equivalent: Art of Electronics (AOE), Section 1.2.3 &1.2.4

Breadboard and multimeter warmup

The circuits in this lab will be built using a solderless breadboard. This breadboardallows you to quickly swap out components, which is useful when you prototype adesign.

a) Using the wire strippers provided in your kit, cut some small lengths of wire andstrip the insulation off the ends to expose the metal. Connect the relevant twoterminals of the multimeter to two of these stripped wires using banana cablesand alligator clips. Using your new probes, figure out which sets of sockets on thebreadboard are connected internally. Sockets that are connected internally shouldideally have no resistance between them.

(15 mins)

Oscilloscope and function generator basics

a) Connect the function generator’s output to the oscilloscope’s input (Channel 1, forexample) using a coaxial cable. Set up the function generator to output a sinusoidalsignal. Vary the voltage and time scale knobs on the scope so that you can fit thewaveform within the screen. (The AUTOSET button is helpful to find a signal, if youthink it might be somewhere way off the screen.) Vary the frequency, amplitudeand DC offset of the function generator, and learn what these do to the signalobserved on the scope.

Set up the TRIGGER settings properly so that the sinusoidal signal is displayedstably on the screen.

You can use the scope’s built-in MEASURE function to directly measure many prop-erties of the signals that you observe.

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PHY 405: Electronics Lab Lab # 1

b) Vary the frequency and DC offset of the function generator, and understand thedifference between AC coupling and DC coupling the oscilloscope. (To emphat-ically see the effect, observe a 1 Hz square wave using DC versus AC coupling.) Inyour report, sketch the equivalent circuit for the input of the oscilloscope under DCcoupling and AC coupling. (You may have to do some research to figure this out.)

c) For more detailed analysis of signals on the scope, you can transfer the scope’swaveform to a computer. Set up the function generator to output a square wave with1 V amplitude. Use the Python program from the course webpage to communicatewith the scope and download a trace of this square wave.

d) Calculate the power spectrum of the trace that you downloaded, using the powerspectrum code from the course webpage. In your report, comment on how thepeaks in the power spectrum are related to the frequency of the square wave.

Note: The resolution of the power spectrum will depend on the total duration of thetrace that you acquired. Observe how the sharpness of the spectrum of a sine wavechanges, as you change the length of the acquired trace.

(30 mins)

Soldering

Although many of the labs will use the solderless breadboard, you will also learn tosolder so that you can build circuit boards in some of the labs and in your projects.

a) Observe the soldering demonstration, and practice soldering some through-holecomponents into a piece of perforated board. Practice the process of un-solderingcomponents.

b) Solder pairs of wires to BNC connectors to construct simple probes, as shown inFigure 1. You can do this task in parallel with the other sections of this lab, to avoidcrowding at the soldering stations.

You can use these probes to measure voltages at different points on the solderlessbreadboard with the oscilloscope and multimeter.

(20 mins)

Voltage source

In this task you will learn how to use a 7805 voltage regulator IC to generate a stablevoltage. The pin labels are listed in the IC’s datasheet, which you can download viathe datasheetcatalog search bar on your browsers.

a) Wire up a 7805 regulator as follows: connect the +18 V output of the HP 6235 DCpower supply to the input pin of the 7805 (pin 1), and connect the ground from thepower supply to the ground pin of the 7805 (pin 2). Measure the DC voltage at the

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PHY 405: Electronics Lab Lab # 1

Figure 1: Wire to BNC adapter. Note that the pair of wires is twisted together and forms a ”twisted pair”.Optionally, the connections between the wire and BNC connector can be covered in heatshrink to preventaccidental shorting.

output of the 7805 (pin 3) using a multimeter or oscilloscope. Verify that the 7805puts out a reasonably constant voltage over a large range of power supply voltages.

Note on capacitors: You will sometimes find capacitors (especially with values≥ 1 µF) that are electrolytic capacitors: these have a specific polarity, and can berecognized by their plastic coated tubular can package. Note their unequal lengthlegs, and the “-” marking on the shorter leg. Make sure that the -ve pin is always ata lower voltage than the +ve pin.

b) Attach resistors ranging from 30 Ω to 1 MΩ to the output of the regulator, andverify that the 7805 puts out a constant voltage regardless of the load resistance.

Figure 2: Circuit for testing the 7805 voltage regulator. Choose the capacitors between 1 nF and 1 uF.

(45 mins)

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