1. Circuits and breadboards:
Name: _____________________________
Date: ____________________________
Approved: ___________________________
Purpose of the lab:
• to analyze circuit theory problems
• to connect electrical circuits
• to measure voltage and current in a circuit
Marks Distribution:
Answer the questions in these instructions. You can do this orally during the scheduled lab session, or
by submitting written answers to your supervisor. Calculations and graphs should be attached if you
make a written report.
Compare measured and calculated values. How do they agree? What is the reason for any
differences?
To pass you must solve tasks 1-3a. Task 3b and 4 are included in the grading of the course.
How to make a design based on circuit diagrams
1) NODES! Recognize which points are the same! Learn to understand how your breadboard
works.
2) Colour Selection: Do not confuse yourself, and be intelligent when choosing cable colours.
Distinguish between positive voltages and ground. You can have as a rule to use red cables
for higher potentials, and black for ground/lower potential. Study your instrument and realize
that their contact clamps are also red at the higher potential and black for ground/lower
potential. This applies to both voltage measurement and current measurement. Try to follow
the colour coding!
3) Try to use as few extra wires as reasonably possible. Take advantage of the breadboard
structure, and make use of any long legs that components might have. Use the Jump-wires
when needed.
4) Be sure to turn components the right way (for e.g. diodes and capacitors)
Follow the wiring diagram around the loops that exist. Start from plus and then work your way
forward using components and measuring instruments.
How do you connect the measuring instruments?
Connect “banana” cables and coupling clamps to the multimeter.
a) Voltage measurement: Is always done in parallel with the components! Connect the
voltage input to the point with higher potential, and the ground input to the point with lower
potential!
b) Current Measurement: Is always done in series with the components. First break the
circuit, and then use the amp meter to close it again.
Measuring with a multimeter:
To get to know the equipment and get used to making connections, we’ll start with the
simple circuit below. The objective is to verify the principles of voltage division.
Figure 1.3
Calculate the line current and the voltage over the 100  resistor for the circuit in the
above figure!
The S111 lab room is equipped with multimeters that are able to make combined
measurements of two quantities. If both voltage and current is to be measured with the
same measuring instrument, it is not possible to connect the multimeter as shown above.
That's because there is only one common negative input (COM) on the multimeter, and it
must be connected to one single node in the circuit. We can solve this problem by moving
the measurement of the current to the negative terminal of the voltage measurement, as
shown below. Note that the ampere meter will be connected “backwards", and that the
indicated power will thus get the wrong sign.
B
220 Ohm
+
00.000
V
-
5V
100 Ohm
+
A
00.000
A
COM
Figure 1.4
Measure the supply voltage. Connect according to the figure 1.4. Measure the voltage
and current.
U = _______
I = _______
How do you select the measurement range of the multimeter to get the best possible
accuracy on the result? (Can you change the measurement range for both voltage and
current?)
_______________________________________________________________!
1.2 Voltage Division and Thévenine equivalent
a) Voltage division
Theoretical task: Calculate UAB,
UAB =
UBC and UCD for the following circuit!
UBC =
UCD =
Connect the circuit and the voltmeter, and check your calculations!
UAB =
UBC =
UCD =
Based on Kirchoff’s voltage law, we know that the sum of the partial voltages is equal to
the supply voltage.
b) Ohm's Law and Kirchoff’s current law
After calculating the voltages in figure 1.5, it is easy to calculate the currents in the circuit using Ohm's
law.
Calculate: I1 =
I2 =
How big is the circuit line current I?
(Kirchoff’s current law)
I3 =
I=
Connect the ampere meter and measure:
I3 =
I4 =
I=
I4 =
c) Thévenin equivalent
Let the circuit from task b remain on the breadboard. Calculate the Thévenin voltage and the Thévenin
resistance between points B and C in the circuit (Figure 1.5). A Thévenin equivalent is a simplification
of a circuit with only two components, as in Figure 1.6. No components should be removed from your
circuit during the calculations. If an additional component is connected between B and C in the
Thévenin equivalent, you will get the exact same current and voltage as if you had connected it into
the real circuit. (The Thévenin theorem assumes linear components, i.e. that Ohm’s law applies.)
B
+
Rthi
U
Vth
C
Figure 1.6
Calculate theoretically:
The Thévenin voltage Vth, (we already know this value from task a!)
The Thévenin resistance Rth =
The Short-circuit current Ish =
Measure
Ish by attaching the ampere meter between B and C!
Ish =
Remove the ampere meter between B and C, disconnect the supply voltage, and replace it with a
shortcut between A and D. Then measure the internal resistance between B and C with the ohmmeter.
Rth =
Hopefully, your theoretical values will match your measured results well!
If not, why is it not perfect? Explain!
1.3 Simulation in Mindi
a) Bridge Networks (lecture 2)
Start the Mindi program on your PC. Draw the circuit below. Insert an Ampere-indicator for measuring
the current indicated by the current arrow. The Ampere-indicator should be connected in series with
the resistance R5. Make sure that the direction of the current source is correct. Use the multimeter in
the program or more indicators to verify that the circuit is working properly.
b) Verification of superposition (lecture 3)
Superposition basically says that you can calculate the currents and voltages in a circuit for one
source at a time, and then add the results. Verify the theorem by measuring the current I for one
source at a time.
Is the sum of I01 and I02 in agreement with the result of task a)?
1.4
Measurement on a light emitting diode
Udiode [V]
1.5
1.6
1.7
1.8
1.9
2.0
2.1
Idiode [mA]
You are going to use the 100 kΩ potentiometer (variable resistance) on your lab board. Before the
circuit is connected, you should turn the potentiometer into its bottom position. Measure between
which of the outer legs and the middle leg you can find the full resistance. Only these two legs shall be
connected to your circuit! We want the current to be as low as possible at the start of the
measurements.
Before connecting the circuit, verify that the supply voltage is 9 Volts. How should the light emitting
diode (LED) be connected? Measure with help of the multimeter.
Perform measurements according to the sample table above (note that you do not have to follow the
table exactly. It might not be possible to reach all voltage values).
At which current value does the LED begin to shine weakly?
I=
Plot the diode’s characteristics in a graph with Idiode on the y-axis and Udiode on the x-axis!
Extrapolate the diode’s threshold voltage (the voltage when the diode begins to lead current) in the
graph.
Utr =