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VE215  Lab 1 DC Lab
1
VE215
Lab 11: DC Lab
Manual
I. Goals for the Lab
i. Learn how to use UT60A multimeter for measurements of voltage, current, and resistance.
ii. Learn to build circuits on a solderless prototype board.
iii. Verify the basic circuit laws –KCL, KVL, and Ohm’s laws from measurements of currents
and voltages.

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## Description

VE215  Lab 1 DC Lab
1
VE215
Lab 11: DC Lab
Manual
I. Goals for the Lab
i. Learn how to use UT60A multimeter for measurements of voltage, current, and resistance.
ii. Learn to build circuits on a solderless prototype board.
iii. Verify the basic circuit laws –KCL, KVL, and Ohm’s laws from measurements of currents
and voltages.
iv. Measure the current-voltage characteristics of a 50Ω resistor. From the results of
measurements, draw the conclusion on whether they obey Ohm’s law.
v. Build an LED circuit on a protoboard and learn about non-ohmic circuit components, which
do not obey Ohm’s law.
II. Experimental Instruments
2.1 Multimeter
A multimeter is able to work as a voltmeter to measure voltages, as an ammeter to measure
currents, or as an ohmmeter to measure resistances.
Every multimeter has two terminals for the two cables that ensure electrical connections to the two
nodes. The black cable should be connected to ground, the ground port is labeled COM on the
multimeter. The red cable should be connected to HzVΩ port for voltage or resistance
measurements, 10A MAX port for current measurements, or μAmA port for small current
measurements.
2.1.1 Voltage Measurements
The voltmeter has its own internal resistance, which is usually very high. For an ideal voltmeter
the input resistance is infinitely large. In real instruments the internal resistance usually exceeds
1MΩ. When we measure VAB the voltmeter’s internal resistance is connected in parallel with all
circuit elements between these two terminals. Note that you do not have to change anything in
your circuit to measure voltage: just connect the multimeter to the nodes of interest.
2.1.2 Current Measurements
To measure the current that flows through a branch of your circuit we should make this current
flow through the multimeter. Note that in order to measure the current we have to interrupt the
circuit: the diagram below shows that instead of one node we work with two nodes A1 and A2.

1
This lab manual is based on Circuits Make Sense, Alexander Ganago, Department of Electrical Engineering and Computer
Science, University of Michigan, Ann Arbor.
VE215 FALL 2016 Lab 1 DC Lab
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The circuits is broken at the point where we measure the current and the ammeter bridges the gap.
The internal resistance of an ammeter is very low, say, 1Ω or less.
2.1.3 Resistance Measurements
To measure the resistance, we simply connect it to the two terminals of the multimeter, and read
the resistance from the display. Remember: you must disconnect the resistor from your circuit
before measuring the resistance! Otherwise, you will not obtain the correct reading of resistance.
2.2 DC source
MOTECH LPS 305 Power Supply2
1. When you press the +Vset, or -Vset, the output selected (+output or –output) and the present
setting for that function will be displayed. You can change setting using the numeric entry
keys. Pressing the number keys will cause the present numeric setting to become blank and be
replaced with the new numbers on the display. Pressing the ENTER key will enter the values
displayed.
2. The selected output channel can be turned on and off from the front panel. The output on/off
key toggles both the +output and –output on and off simultaneously.
3. Remember to turn off the output when no measurements are being undertaken.

2
This part is based on LPS 305Linear Programmable Power SupplyUser’s Manual, MOTECH
VE215 FALL 2016 Lab 1 DC Lab
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Agilent E3631A DC Power Supply3
To set up the power supply for constant voltage (CV) operation, proceed as follows.
1. Connect a load to the desired output terminals with power-off.
2. Press to turn on the power supply. The power supply will go into the power-on / reset state; all
outputs are disabled (the OFF annunciator turns on); the display is selected for the +6V supply
(the +6V annunciator turns on); and the knob is selected for voltage control.
3. Adjust the knob for the desired output voltage. Set the knob for voltage control. The second
digit of the voltmeter will be blinking. Adjust the knob to the desired output voltage.
2.3 Protoboards
In this lab and all the future labs, you will connect resistors, LEDs and other components to each
other on a circuit board. Circuits boards are also called “protoboards”, because they are used for
prototyping the circuits. Another name is “breadboard”, because in old times circuits were indeed
built on wooden breadboards. The main idea is to build the citcuit without soldering every
connection thus the long generic name is solderless prototyping boards.
A prototyping board used in the lab consists of several plastic blocks. These plastic blocks are
mounted on a metal plate along with terminal (blind) posts.
Each plastic block has many holes, into which you insert wires, plug in resistors, op amps, and
other circuit components. Inside the plastic block, themetal clips snugly hold your wires, resistors,
etc., and ensure electric connections between circuit components.

3
This part is based onAgilent E3631ATriple OutputDC Power Supply User’s Guide, Agilent Technologies, Inc.
VE215 FALL 2016 Lab 1 DC Lab
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These metal clips hidden under the plastic create nodes on the protoboard, to which you connect
Connections under the plastic are different for the wide and narrow blocks.
Straight lines on the diagram above show the metal clips that connect holes under the plastic.
Remember how the holes are connected into nodes on a circuit board. Many students’ mistakes in
the lab are due to forgetfulness of how the nodes are organized.
2.4 Semiconductor diodes
The simplest semiconductor device is a diode. Its circuit symbol looks like an arrow because the
diode allows the current flow only in the direction of that arrow. If ??>?? (which is called direct
bias) the conductor will conduct. If ??<?? (which is called reverse bias) the conductor will not
conduct. Thus a diode is not an Ohmic resistor.
Moreover, even under direct bias the resistance of a diode does not remain constant. At small
values of the voltage difference ??−?? the current through the diode is very small, because its
resistance is large. The diode’s resistance abruptly changes as soon as the direct bias voltage
across the diode reaches the threshold value, which is called the turn-on voltage and equals about
VE215 FALL 2016 Lab 1 DC Lab
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0.5 to 0.7V for many diodes. Above this voltage the current through the diode rapidly increases
and becomes practically independent of the voltage. The diode resistance becomes so small that in
real circuits the diodes have to be protected from high currents that may damage them. A load
resistor (50Ω in this lab) connected in series with the diode ensures the simplest protection.
Light-emitting diodes emit light (visible or infrared) when the direct current becomes large enough.
The LED, which you will use in this lab, has the turn-on voltage of about 1.6V.
III. Pre-lab assignment
Finish it before labor you lose your score for this part
3.1 The ohmmeter’s equivalent circuit,
shown in the diagram, includes a small
voltage source ?? (usually, about 1V)
and the resistance ??, which both
belong to the internal circuitry of the
instrument.
When the resistor R is connected between the terminals labeled HI and LO, the circuit becomes a
voltage divider. Then the instrument measures the voltage between the terminals HI and LO, or the
current through, uses the formula for voltage division, calculates the resistance R and displays it in
the units of ohms. Now explain: why the resistor must be disconnected form the circuit before
measuring the resistance?
3.2 For each pair of resistors on the protoboard shown below determine how they are connected
with each other (in series, in parallel, etc.).
3.3 According to the description in part 2.4, roughly sketch the voltage-current characteristics
curve of a common LED.
IV. Procedures
4.1 Voltage, Current & Resistance Measurement
a) Use the multimeter to measure the resistance R1 labeled 100Ω directly and record the
result.
VE215 FALL 2016 Lab 1 DC Lab
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b) Connect the resistance R1 = 100Ω with the power supply and set the voltage 3V.
c) Use the multimeter to measure the Voltage (m) across the resistor and compare it with the
Voltage (s) shown on the power supply.
d) Use the multimeter to measure the Current (m) through the resistor and compare it with
the Current (s) shown on the power supply.
4.2 Voltage Division & Current Division
a) Before measurement, measure the actual resistances of the two resistors you are using in
this section.
b) Connect the R1 = 100Ω and R2 = 50Ω in series and in parallel, respectively.
c) Use the multimeter to measure the voltage across the R1, R2 and the power supply, and
think about the relationship among the three voltages.
d) Use the multimeter to measure the current through R1, R2 and the power supply, and
think about the relationship among the three currents.
e) Compare the result with what you expect.
4.3 Ohm’s Law
a) Measure the resistance of R = 50Ωand record the result.
b) Connect the R with the power supply.
c) Set the voltage outputs and record the corresponding currents.
d) Sketch the voltage-current characteristic curve of the resistor.
4.4 Non-ohmic LED
a) Connect the resistor R = 50Ωand the LED in series with the power supply.
b) Change the voltage output and record the corresponding current.
c) You need to design the proper step of voltages to get the voltage-current characteristic of
the non-ohmic device.
Reference:
1. Circuits Make Sense, Alexander Ganago, Department of Electrical Engineering and Computer
Science, University of Michigan, Ann Arbor.