Dalhousie University Faculty of Engineering
Department of Electrical and Computer Engineering
ECED 2000 Electric Circuits
Lab1 Introduction to Electrical Measurement
Objective:
-To become familiar with electrical test equipment.
-To master fundamental electrical measurement techniques.
1) Equipment
You will need the following equipment to do this lab:
1 DC Power Supply (on bench)
1 Multimeter (on bench)
1 Prototype development board (obtain from tech office-sign out)
1 Blue LED (C503B-WAN-CCAAB151-ND)
1 x 1000 1% resistor
Wires (supplied)
2) Procedure
a. Prototype board (breadboard): Most of the circuits you will construct in this
lab will be placed on what we call a “proto” board (or breadboard) and you
will need to know how this useful design tool is constructed. Figure 1 shows a
typical breadboard and the way it is connected. Note in the center there are
columns of five holes each that are all connected internally so that up to five
wires can be connected together by inserting wires into these holes (there is a
metal spring clip under the hole which holds and connects the wires). At the
top and bottom are longer connecting “rails” (designated by red and blue
stripes) which are used to provide power or ground to many circuits along the
length of the board.
b. Circuit resistors: All printed circuit board resistors are colour coded so that
the value of resistance may be determined. The following shows the colour
values and how to determine the resistance. All of the computers in the lab
have a colour code tool installed if you can’t remember the colours.
Black Brown Red Orange
Yellow
Green
Blue
Violet
Grey
White
0
4
5
6
7
8
9
1
2
3

First find the tolerance band, it will typically be gold ( 5%) and
sometimes silver (10%).

Starting from the other end, identify the first band - write down
the number associated with that color; in this case Blue is 6.

Now 'read' the next color, here it is red so write down a '2' next
to the six. (you should have '62' so far.)

Now read the third or 'multiplier exponent' band and write
down that as the number of zeros.

In this example it is two so we get '6200' or '6,200'. If the
'multiplier exponent' band is Black (for zero) don't write any
zeros down.
Taken from http://wiki.xtronics.com/index.php/Resistor_Codes
Resistors or other circuit components are connected together on the
breadboard as shown
c. Power Supply:
In order to make a circuit “do” anything it usually needs to
have “power” applied to it. In most situations this consists of applying a
voltage potential across a pair of terminals or injecting a current by means of a
wire connecting the power supply with the circuit. You will now use the
power supply located on the bench in front of you to apply a voltage to a
circuit that you will soon construct (these power supplies are dual supplies and
you will only be using one of the two supplies). The “RED” terminal is the
high potential side (+ve) and the “BLACK” terminal is the low potential side
(-ve). The “GREEN” terminal is chassis ground and is not needed at this time.
In order to apply the voltage you must turn the supply on and press the
“enable” button (if present). Turn the current control to max (clockwise) and
then use the voltage control to adjust the output to 10V.
d. Voltage measurement: You have also been supplied with a voltmeter.
Ensure it is set to measure voltage (not current or ohms) by pressing the
appropriate buttons. Ensure it is set for DC voltage (not AC). Select a scale
that will allow the measurement of 10 V. Place the leads across the terminals
of your power supply (red to red and black to black) and record the voltage. If
it is not exactly 10V adjust your power supply control until it is. Reverse the
terminals of the meter and
record your result (polarity
has to do with the direction
with which the potential is
applied and/or measured).
e. Current Measurement: Current measurement is a little harder than voltage
measurement because you have
to “open” the circuit in order to
insert the ammeter so that the
ammeter “sees” the same current
as the circuit elements (The
Ammeter and the circuit element
must be in SERIES). Assemble the components of the figure below and
ensure your circuit is working by applying power. Your LED should turn ON.
Measure the current through the diode by following the steps shown.
Step 1. Create your circuit
by applying 10 V to the
diode-resistor circuit.
Step 2. Break (or OPEN) the
circuit where you want to
measure the current
Step 3. Insert the ammeter to
complete the circuit you just
opened
Before inserting the ammeter make sure your power supply is turned OFF and
disconnect your voltmeter. On the multi-meter panel select DC amps and place
the leads in the appropriate terminals to make your multi-meter into an Ammeter.
Get me (or a T.A.) to check your wiring before turning the power on!
Here the polarity is defined as the current flowing from left (Red Lead) to right
(Black Lead). Turn the power ON and record your circuit current. Reverse the
ammeter leads to see the polarity change (i.e. if the current from right – to – left is
-10 mA, it is the same as saying the current from left-to-right is +10mA).
Ohm’s law tells us that the resistance of a circuit is the ratio of the voltage applied
across it to the current
flowing through it
(R=V/I). Calculate the
actual resistance of the
1000  (i.e. 1k) resistor
by measuring the voltage
across and current through
the resistor (two separate
measurements- remember
to change the meter
terminal jacks). Is the
resistance value within the
resistor tolerance value?
Answer the following questions:
What current causes the LED to light up?
What is the voltage across the LED when it first lights up?
What current flows when you apply 15V to the combined series circuit?
What is the LED voltage when you apply 15V across the whole circuit?
What is the resistor voltage when you apply 15V across the whole circuit?
f. Ohmmeter:
Your multimeter can also be used as an Ohmmeter.
Disconnect your circuit so that the resistor stands alone and unconnected to
other circuit elements, make the appropriate meter selections and wiring to
measure the resistance of the 1k resistor and compare them with your
calculations. Go to the resistor bucket at the front of the room and select two
or three random resistors. From the colour code determine the nominal
resistance value and then use your Ohmmeter to measure the value. Compare
the results.