PHY 405: Electronics Lab
Lab # 1
Lab # 1: Measurement basics
In this lab you will learn how to use the basic tools and instruments in the lab. You
will build some voltage dividers, and understand how to use a voltage regulator IC.
Throughout this course, you will find it useful to roughly plot data in your notebook as soon as
you make measurements. Plotting your data as soon as you acquire it will help you to understand
what you are doing better, and to quickly identify if there are any problems. You can produce
higher quality plots on a computer later, when you write your report.
Background preparation
• Oscilloscope (“scope”) basics: introductions posted on the course webpage.
• Function generator: Instek SFG-2000 manual posted on the course webpage.
• Voltage dividers: AOE, pages 3-10.
• Voltage regulator: LM7805 datasheet, available using the datasheetcatalog
search function on your web browsers.
Task 1: Breadboard and multimeter warmup
All your circuits in this lab will be built using a solderless breadboard. This breadboard
allows you to quickly swap out components, which is useful when you prototype a
design.
a) Using the wire strippers provided in your kit, cut some small lengths of wire and
strip the insulation off the ends to expose the metal. Push the exposed ends of the
wire into the solderless breadboard, and use a multimeter to figure out which sets
of sockets on the breadboard are connected internally.
(10 mins)
Task 2: Oscilloscope and function generator basics
a) Connect the function generator’s output to the oscilloscope’s input (Channel 1, for
example) using a BNC cable. Set up the function generator to output a sinusoidal
signal. Vary the voltage and time scale knobs on the scope so that you can fit the
waveform within the screen. (The AUTOSET button is helpful to find a signal, if you
think it might be somewhere way off the screen.) Vary the frequency, amplitude
and DC offset of the function generator, and learn what these do to the signal
observed on the scope. In your report, sketch a sinusoid and label its amplitude,
frequency and DC offset.
You can use the scope’s built-in MEASURE function to directly measure many properties of the signals that you observe.1
1 For more detailed analysis of signals on the scope, you can transfer the scope’s waveform to a computer.
Lab # 3 will teach you how to use Python programs to communicate with the scope.
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PHY 405: Electronics Lab
Lab # 1
b) Set the function generator’s output to 3600 Hz. Adjust the trigger setting of the
scope to display a steady signal. Try to set the input channel (e.g., Channel 1) as
the source for the trigger. Once you get a steady signal with this, try using the AC
line as a trigger source. Report on what happens to the AC line-triggered waveform
when the function generator is set to 3610 Hz. Why do you think this happens?
(40 mins)
Task 3: Resistive and capacitive dividers
a) Build a resistive divider on the solderless breadboard. First build a divider using
two resistors (both ≥ 1k).2 Using the function generator as the input to the divider,
measure the output using a scope. Report the voltage division ratio (Vout /Vin ) of
the divider at a set of 5 frequencies between DC and 1 MHz.
b) Build a resistive-capacitive divider: wire up a resistor and a capacitor in the configuration shown in Figure 1. Choose an R between 1k-1M, and a C between 0.01uF
- 1 uF (clearly record and report the values of R and C). Report on the division
ratio that you measure for this divider at 10 different frequencies between DC and
1 MHz: plot the voltage division ratio versus the AC frequency on a loglog plot,3
and comment on the action of this divider.
In your report, explain why this divider acts the way it does. (Hint: think about the
impedances of the resistor and capacitor.) Comment on what you might use such a
divider for.
Vin
R
Vout
C
Figure 1: Circuit diagram for the resistive-capacitive divider.
Extra credit: Build a capacitive divider: replace the two resistors from (a) with two capacitors
(both ≥ 10 nF). Report on the voltage division ratio that you measure for this divider
at a number of frequencies between 10 Hz and 1 MHz, and plot it as before. What is
the response of this circuit to a DC voltage at the input?
(1 hr 20 mins)
2 “1k”
is a common way to write 1 kΩ. You will see that the Ω symbol gets dropped on many circuit
diagrams. This is one of the very few places in physics where it is (somewhat) pardonable to drop the symbol
for a unit.
3 That means base 10 logarithmic on both the x and y axes.
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PHY 405: Electronics Lab
Lab # 1
Task 4: Voltage regulators
In this task you will learn how to use a 7805 voltage regulator IC to generate a stable
voltage. The pin labels are listed in the IC’s datasheet, which you can download via
the datasheetcatalog search bar on your browsers.
a) Wire up a 7805 regulator as follows: connect the +18 V output of the HP 6235 DC
power supply to the input pin of the 7805 (pin 1), and connect the ground from
the power supply to the ground pin of the 7805 (pin 2). Measure the DC voltage at
the output of the 7805 (pin 3) using a multimeter. Vary the output voltage of the
HP 6235, and report on the range of power supply voltages over which the 7805
outputs a stable voltage that is within spec.
b) Now you will measure the voltage fluctuations at the output of the 7805, using the
oscilloscope. Switch the scope channel to AC coupling, zoom in appropriately
with the voltage scale knob, and report the rms (root mean squared) value of the
noise that you observe.
c) Connect capacitors across both the input and the output, as shown in Figure 2.
(Try using capacitors with values between 1-100 uF.) Measure the rms noise on
the output voltage. Based on your measurements, comment on the purpose of the
capacitors.
1
Vin
7805
Vout
3
1M
2
C
C
SCOPE
Figure 2: Circuit for testing the 7805 voltage regulator. The TDS 210 scope has an input impedance of ∼ 1
MΩ.
(40 mins)
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