Laboratory Experiment 1 Circuits, Meters and Measurements)

ELEC1000 – Introduction to Electrical Engineering

Laboratory Experiment 1 - Circuits, Meters and Measurements

Page 1 of 14


Laboratory Experiment 1

Circuits, Meters and Measurements

Work in Groups of two – share the workload. Don’t be the student who fails the

prac exam because they watch a classmate do all the work

You can either write answers on a hardcopy of this laboratory sheet, or you may

prefer to keep a lab notebook (A4 exercise book) with answers to all the

experiments.

Key to success – keep physical notes. Write your results as you go

Aim: To understand:

Basic electrical components and equipment

Safe wiring and colour standards

Simple measurements

Basic voltage and current laws

Measurement errors

Linear and non-linear components

Equipment Adjustable Power Supply

Two or three multimeters (measure current, voltage, resistance)

Prototyping Board

Patch Wires with banana plug connections

Patch Leads

Components:

Resistors: 100 ohm, 120, 1K, 3.3K, 4.7K, 10M (x 3)

LED (Light Emitting Diode) – any colour

Equipment Notes:

The tutors will run through the operation of the equipment at the start of the laboratory

experiment, and at stages throughout the experiment as new equipment is introduced.

In this experiment you will be introduced to fundamental lab equipment which is used

to construct, power and measure circuits and signals. You will be working with passive

components inserted in prototyping boards (also called breadboards, as circuits used to

literally be built on boards made for cutting bread. The wires were held in place with

thumbtacks). We will use the terms breadboard, protoboard, prototyping board

interchangeably. A circuit consists of one or more components arranged with some

power source and possible load devices. Then we can measure voltage, current or

resistance with appropriate connections. If you’re not familiar with the terms, ask your

tutor/s about them.

On the following couple of pages you will see pictures of the equipment you will use.



Page 2 of 14

You will work with the following two-terminal devices:

Figure 1. Symbols and pictures

What you see next is a multimeter, which has its measuring leads and selector arranged

to measure different electrical signals. The “ohm meter” is just the multimeter wired up

to measure resistance in ohms. A short circuit is usually zero ohms, but could read up to

2 ohms due to resistance in the measuring leads. An open circuit is usually hundreds or

thousands of millions of ohms. This is usually displayed as “1.” followed by blank

digits or “OL”, which stands for overload.

Multimeter wired for OHMS Multimeter wired for DC Volts

Multimeter wired for mA Multimeter wired for DC 20 Amps range

Figure 2. Various multimeter connections



Page 3 of 14

Picture 1. One type of setup for measurements.

In the picture above, you can see a power supply, meters, prototyping board, banana

leads, patch wires and components.

Prototyping board

The small holes in the board allow electrical connection to wires and component leads.

Some of these holes are connected together, so use patch leads to connect between

desired “nodes”. For convention and ease of interpretation the paired rows at the top

and bottom of the board are used for power rails and ground. Note that they may not be

continuous across all protoboards .

Note that the coloured posts around the protoboard are not connected to it until YOU

join them with patch wires. If you look at the picture below, the top horizontal holes are

highlighted with different colours. All the pink holes are joined together in groups of

25, under the board, as are the green ones, but the green and pink holes aren’t joined

unless YOU join them with wires. The purple vertical holes are joined in groups of 5

but they are not connected to their neighbouring columns, or the horizontal rows until

YOU join them.

Figure 3. Detail of white proto board



Page 4 of 14

The pictures here show see-through views of various protoboards. The top picture

shows horizontal connections all the way across the board. SOME BOARDS HAVE A

BREAK IN THE MIDDLE, so beware. The bottom right part of figure 4 shows the

metal strips that are behind each group of holes. These strips are like pegs which hold

the wires in place and they can hold 5 or 25 wires.

Figure 4 - View of insides of proto boards

Figure 4 is courtesy of http://www.robotroom.com/Solderless-Breadboards.html

For more pictures and examples of using breadboards try the following web links:

http://electronics-madeeasy.blogspot.com/2011/01/bread-board.html

http://www.web-books.com/eLibrary/Engineering/Circuits/DC/DC_5P8.htm

Figure 5 Banana plugs Figure 6 Pliers and wire strippers

http://www.robotroom.com/Solderless-Breadboards.html

http://electronics-madeeasy.blogspot.com/2011/01/bread-board.html

http://www.web-books.com/eLibrary/Engineering/Circuits/DC/DC_5P8.htm



Page 5 of 14

Figure 7. White protoboard with banana plug posts

As you can see there are different types of breadboards.

Figure 8. Blue proto board with slightly different power rail connections to the white board

The large “banana plug” sockets (posts) allow connections to patch leads, and the holes

at the base of each socket allow the screw-down terminals to connect to patch wires.

The posts are electrically isolated from the metal frame they are mounted in. Make sure

that any wires pushed through the hole in the base of each post do not have insulation

covering the end, or you will not have a proper electrical connection.



Page 6 of 14

Power supply

Figure 9. Laboratory power supply

In Figure 9, you can see controls for current and voltage. At the very bottom-right of

the power supply is a fixed 5VDC output, limited to 3 amps maximum output.

There are also two variable-output connections with 3 terminal posts. These have a

maximum output of 32 Volts DC. The right-hand side of these two has been setup for

10 Volts DC and the cables would be plugged in to the black and red terminal posts just

below the words “Tracking” and “Master”.

Tracking: You can see some buttons below the words “Indep.”, “Series” and

“Parallel”. These allow the two different variable sections to be used in different ways.

Independent: The output voltages and current are unrelated to each other, so one

output could be 7.5 volts, while the other is 24 volts.

Series: This allows either a higher voltage than 32 V, or to treat the system as having a

positive and negative voltage rail of up to 30 V, i.e. + and – 15 volts. The black

terminal of the left output will be the negative voltage rail. The black terminal of the

right output will be the zero volts rail, and the red terminal of the right output will be

the positive rail.

Parallel: This combination allows more than 3 amps to be supplied to a circuit, so the

power supply can deliver the same voltage on each of the outputs, but up to 6 amps

maximum.



Page 7 of 14

The terminal posts have a through-hole in them where the joiner wire goes. It is

important to make sure that only wire sits in this hole. If you push the wire too far

through, then only insulation will be attached and no electrical circuit exists.

Through-hole in terminal post Correct method of placing wire in through-hole

Wrong placement of wire Screw post down until wire is held firmly

Preferred method for stripping insulation from wires



Page 8 of 14

Circuits on a breadboard:

Figure 10. Example layout of protoboard. Figure 11. Placement of components in protoboard

The figures above show how to layout the components on the protoboard.

Figure 10 shows the approximate layout for Part 3 of this laboratory.

Figure 11 shows the incorrect placement of a component on the left. The resistor is

shorted by the segment as all 5 of the holes in the segment are at the same voltage.

The resistor on the right spans the gutter, which insulates the two segments. Thus the

resistor on the right can have different potentials on each leg

Part 1. - A simple electric circuit.

Here you will use one of the variable power supply outputs and adjust the voltage

control whilst observing the values on the voltmeter. The panel meters on the power

supply are fairly coarse and show only the approximate voltage i.e. ~ 5 volts, whereas

the voltmeters show a more precise value, i.e. 5.13 volts

The symbol on the left is for the power supply, the one on the right is for a voltmeter.

Connect up the following circuit, and adjust the power supply to give voltages of

approximately 2V, 5V and 10V displayed on the voltmeter. Repeat with the other

voltmeter if it is a different model.



Page 9 of 14

Part 2. – Simple Measurements.

Vs is the Voltage Source, which is the power supply.

Is is the supplied current,

V1 is the MEASURED voltage.

You may remember that current, I, is equal to the voltage V, divided by the resistance

R, so I = V/R. This is also V = IR, R = V/I.

Refer to Picture 1 for a rough idea of layout and connections.

To measure current in this circuit we select the mA range on a meter, place a red lead

between the positive terminal (RED) of the power supply and the mA or A terminal on

the meter, then place another red lead between the COM terminal of the meter and one

terminal post on the protoboard. Next, we take a black lead from the negative post

(BLACK) of the power supply and connect it to a suitable post on the breadboard.

Now place the resistor in a suitable position in the breadboard and connect jumper

wires from the selected posts to the ends of the resistor. To measure the voltage, you

can connect suitably coloured leads from a second meter to the posts you have just

wired up.

Connect up the following circuit, and measure the current and voltage, for voltages of

approximately 2V, 5V and 10V.

Meter voltage Measured Volts Theoretical current

mA

Measured current mA

2

5

10



Page 10 of 14

Part 3. – Kirchhoff’s Laws See Figure 10 above for hints on layout. Connect up the following circuit, and

measure each of the indicated currents and voltages. You won’t have enough meters to

measure everything simultaneously, so use the probes on the voltmeter to “walk

around” the circuit

Current loops in the circuit. Meter probes used to “walk around”.

Theory - You will cover this in week 2 of lectures.

Voltage:

KVL is written in terms of symbols (such as Vs) for each loop; confirm that it is correct

from your experimental measurements.

Loop 1: Theory Vs = V1 + V2

Experiment ....................................................

Loop 2: Theory V2 = V3.

Experiment ....................................................

Loop 3: Theory VS = V1 + V3

Experiment ....................................................



Page 11 of 14

Current:

Confirm Kirchhoff’s Current Law (KCL) experimentally at each node:

Node A: Theory I1 = I2 + I3

Experiment ....................................................

Node B: Theory Is = I1

Experiment ....................................................

Ground: Theory I2 + I3 = Is

Experiment ....................................................

Power:

Now calculate the power supplied by the power supply: Ps = Vs.Is .....................

Calculate the power dissipated by each Resistor, and the total

P1 = V1.I1 = ............................... P2 = V2.I2 =.......................................

P3 = V3.I3 = ..........................

Power Delivered by Source = Power Consumed.

PS = P1 + P2 + P3.

PS = ……...……….. P1 + P2 + P3 = ...................................................



Page 12 of 14

Part 4. Measurement Errors: Construct the following circuit, and measure each of voltages: VS, V1, V2, V3

We would expect V1 = V2 = V3 = 2V.

Is = Vs / Rtotal = 6V / 30 Meg ohms.

We would expect the current Is to be 200nA.

HOWEVER, a voltmeter draws a current of perhaps 10-100 nA to make its

measurement and this influences the result for circuits with very low currents. Current

meters can similarly affect circuits where voltages are very small, SO BEWARE!

Voltage Theory Measured

V1 2

V2 2

V3 2

Q. Are the measured voltages different to the theory? If so, why?

A. .......................................................................................................................................



Page 13 of 14

Part 5 – Linear Components (Ohm’s Law) Vary the power supply so as to measure the voltage, V1, for the following values of

current: (The ammeter can be placed between Vs and the 120 ohm resistor –like Part 2)

Current 1mA 2mA 5mA 10mA 15mA 20mA 25mA

Voltage

V1

Vs

Plot V1 versus I1.

You should get a straight line through the origin.

This is a LINEAR component.

The slope of the line should be the resistance.

You can also plot Vs versus I1 on the same graph.



Page 14 of 14

Part 6 – Non-linear component. Vary the power supply so as to measure the voltage, V1, for the following values of

current: (The ammeter can be placed between Vs and the 120 ohm resistor –like Part 2)

Current 1mA 2mA 5mA 10mA 15mA 20mA 25mA

Voltage

V1

Vs

(Note: if LED is not “on” for voltages above about 3V, and current remains low, LED

is probably in backwards! – reverse it). The shorter lead is the cathode, which is

connected to the negative supply.

Plot V1 versus I1. You should get a curved line. This is a NON-LINEAR component.

Once again, you can also plot Vs versus I1 on the same graph.

END OF EXPERIMENT

Documents

Laboratory Experiment 1 Circuits, Meters and Measurements)