MTRX1705: Introduction to
Mechatronic Design
Week 2, Introduction Lab
THIS SHOULD TAKE AN AVERAGE STUDENT 3 HOURS TO COMPLETE.
Summary
This tutorial is for students to evaluate their own level of understanding about electrical
circuit theory and develop some simple electronic lab skills. Some students will find this new,
others will have seen this many times before – this is the difficulty with the first lab for first
year students, we need to get you all up to speed before we begin the more serious stuff. For
those of you that are familiar with the content, try creating more complex circuitry on your
breadboards or playing around with the oscilloscopes. If this content is unfamiliar, I suggest
that you complete ALL the activities, ask others (tutors and classmates) for help and also seek
out other similar questions online or in the textbook
This needs to become second nature to you !
Parts list
Resistors (approx 0.25 watt) of various values (390, 470, 1k, 10k). A number (10+) of each of
these values will come in handy during the semester.
LEDs (recommend 5mm) various colours (red, green). A number (5+) of each of these would
be useful and will be used throughout the semester.
Button (push button) that can fit in the centre of the breadboard. An example of this is rs
electronics part no. 4791435 though any button that fits would be suitable.
Wire (single core hookup wire) of various colours. Having different colours will make it easier
to build circuits that other people can understand. Please note that it must be single strand
(only one core of wire) as multi-strand will not insert correctly into a breadboard
Theory
Review this module in canvas (Module 1: Introduction to mechatronic systems). If any of these
concepts don’t make sense, this is a good time to follow up (ask tutors, post to the Ed forum,
etc).
Practical
Lab work deals with familiarisation of basic electronics. We will experiment a little bit with
multimeters, a couple of components and your breadboard. If you have not obtained your own
breadboard yet, you are already falling behind. You should try to complete at least one
functioning on/off switch today.
Theory
Basic Electric Circuits
1. Electrical Power is defined by P = V*I
Where P is the power (measured in Watts), V is
the voltage (Volts) drop across a device, and I is
the intensity of the current (Amps) through a
device.
In the figure on the right, the “device” is shown as
a resistance, R. The resistance of R is 10Ω. The
battery voltage (E) is 10V.
a. Calculate the current through the resistance, R.
b. Calculate the power that is consumed by the resistance, R.
2. The most common resistors you will find in the lab are rated at a
maximum power of 0.25 watts. Above this, the resistor will
overheat and get damaged.
a. Calculate the minimum resistor (R1) that you can safely
connect to a 5 volt power source. You can work this out
using the definitions of power (P=IV) and resistance
(V=IR).
3. It is important to understand how to measure voltage and
current in a circuit, as voltage and current are measured using
different circuit configurations.
a. Use the symbols for a voltmeter and an ammeter as shown in Fig. 3 to draw (in
your lab books) a circuit that measures the voltage and the current of the
resistor circuit.
Figure 3: Simple resistor circuit and the symbols for an ammeter and voltmeter
4. Two circuits are shown below. If R1 = R3 = 500Ω, and R2 = R4 = 1000Ω, answer the
following:
a. Are the resistors connected in series or parallel?
b. Calculate the current through each resistor (R1, R2, R3, R4)
c. Find the value for each voltage (V0, V1, V2, V3, V4)
Intuition: a small resistor (i.e. 1ohm) is almost a short circuit (large current)
and a large resistor (i.e. 1M ohm) is almost an open circuit (small current). This
is why we are concerned with the smallest valued resistor with a circuit with
resistors in parallel, as the smaller the resistance, the larger the current.
5. Light emitting diodes (LED’s) are very common in
electronic circuits. They are often used as indicators,
for demonstrating the current state of the device. To
conduct, they need to have as a minimum the
forward voltage, which varies between devices. Less
than this voltage, the current does not flow and the
LED does not emit light. This can be modelled as a
voltage drop across the device. Given this, answer the
following:
a. Use the datasheet for a typical 5mm LED. For
this exercise, we will select this one from
sparkfun https://www.sparkfun.com/products/9590 . For this device, find what
the expected voltage drop (the forward voltage) will be, and the current that is
appropriate (the forward current) when the light is ON.
b. The forward voltage you have obtained will be the voltage drop across L1. Given
this, what must the voltage drop be across R1 (use Kirchoff’s voltage law).
c. Given the forward current you have obtained, what is the value of R1 that you
should use to make the light a reasonable brightness (Ohms law)
Laboratory Exercises
When your theory is complete (in your lab book), show your answers to your tutor to obtain
the following: some wire, 2 LEDs and some resistors (100Ω, 200Ω, 500Ω, 1000Ω, 10kΩ). You
should have your own breadboard and some basic tools.
The multimeter can function as both a voltmeter,
ammeter and an ohmmeter. Multimeters have
different sockets for the probes depending on what
you are measuring. It is important if you are
measuring current that you triple check what you
are measuring.
The COM (common) or ground probe is the same
for measuring current or voltage. The measurement
of voltage or current is a value relative to this
connection.
LOOK AT THE SPECIFIED MAXIMUMS FOR EACH
PORT - THIS IS IMPORTANT !!
TO PREVENT DAMAGE TO THE MULTIMETER
make sure you do not exceed these values.
Sometimes there might be a fuse inside which will
blow but for cheaper multimeters it is possible
(maybe likely) that permanent damage will occur if
you exceed the rated values.
Remember: When measuring current (ammeter) the multimeter acts like a short circuit
(Q3 from the prework). If you measure current with the probes between the positive supply
voltage and ground, you will likely break your multimeter !!. Do not attempt to do this
until you are absolutely sure you understand this - Ask a tutor !
Familiarisation
1. Measure the resistance of the resistors using the multimeter. Consider labeling them so
you don’t forget which is which.
a. Resistors aren’t perfect. How close (%) to the expected value are these
resistors? Compare this to the expected tolerance (last band of colour)
2. Practice cutting wires to length and stripping just enough to allow it to plug into your
breadboard.
3. Measure the resistance of wire of different lengths. What is the resistance? Why?
Working in the lab
Get to know the power supply: there are three sources (channels)
Remember: Don’t enable the output (top left button)
UNTIL you are sure that the voltage is correct
AND your circuit is correct
CH1 and CH2:
The voltage is controlled with the voltage dial. The maximum current is
controlled by the current dial. The current consumed by the circuit depends
only on the resistance of the circuit. The maximum current is the level at which
the power supply will shut off.
You should set the maximum current to a reasonable amount for your circuit
(plus a margin of error). For each circuit, you need to calculate what this is.
CH3:
This voltage is fixed to 5 volts with a fixed maximum of 3 amps. This means that
it will supply the current the circuit would draw given the resistance until the
current is more than 3 amps at which point the power supply will shut down. Be
careful with this supply, 3 amps is enough to damage components when
connected incorrectly.
4. Select CH1 or CH2 from the power supply
a. Set it to 5V
b. Connect the 5V to the main rails of your breadboard.
c. Confirm that the power is connected to your board by measuring the voltage at
different points on the breadboard.
d. Turn off the power source.
Working at home
To run circuits at home, the easiest way to supply power is using a breadboard power module
(seen in the picture above). This requires a usb power cable (the type depends on the model of
the power supply). The one in the image above uses a USB-A connector, which is not very
common (a cable with USB-A on both ends), but if you get one of these it should allow you to
connect a normal USB power supply such as a phone charger to power the breadboard.
Most of these power supplies are the same: there is an on/off power switch, DC in (in case you
have a compatible dc power supply, USB in (in case you want to connect to a usb power
supply) and some selector pins that determine what voltage you want on the power rails (3.3
or 5v). You should select 5V for both rails.
PLEASE NOTE:
With the breadboard power supplies, the maximum current is limited to around 500 mA or so.
I have tested a few and they seem to usually have protection against accidental short
circuiting, but this is not guaranteed. We will cover more on this in a later lecture.
5. Build both the circuits from Q4 of the pre-work on the breadboard.
a. Record the voltages.
b. Record the current: NOTE: RE-READ THE SECTION AT THE START OF THE
LABORATORY EXERCISES ABOUT HOW NOT TO BREAK YOUR MULTIMETER
c. Read the current consumption indicated by the power supply. Is this close to the
value measured by the multimeter ?
d. Are they what you calculated in Q4? Why or why not?
6. Connect an LED circuit as shown in Q5 of the prework. You will need to use a resistor something close to the value you calculated. This will have an effect on the brightness.
a. Measure the voltage across the LED, is it what you expected ?
b. Measure the current through the LED, is it close to the expected forward
current?
Module development
Basic On/Off Switch or Signal Generator
1. Throughout this course, you will be using push buttons to generate a signal as an input
for various circuits. Pick up a push button and (approximately) 10k resistor for the next
steps. Next, On your breadboard, build the circuit shown in Figure 4.
Build these circuits (one at a time)
Figure 4. Three potential switch circuits
Circuit notes:
● This design could be used in the future as a “signal generator”
or “on/off” switch.
● If available, you can connect a push button or electrical switch
but you could even just manually connect and disconnect
a wire by hand from a spot on the breadboard.
2. Testing (use multimeter): For each of the signal generator circuits, record
a. When the switch is “on” or connected what is the output voltage?
b. When the switch is “off” or disconnected, what is the output voltage?
c. What signal (voltage) is the default output - i.e. what is the voltage when the
button is not pressed ?
3. Failure modes
Consider the following circuit (DO NOT MAKE THIS CIRCUIT)
a. What is the voltage when the switch is open and closed?
b. What is the current when the switch is closed ?
c. What would happen to the power supply in this case ?
4. Discovery
In future labs, you will use this switch circuit as a means of setting the input to a logic
device. The LED (or display) circuit will be used as a means of visualising the output of
a logic device. Consider these two circuits as functional blocks (modules)
Consider the following circuits: Pick one and build it (you can just connect directly the
circuit points A and B since there is no logic device yet)
For the circuit you built:
a. Which button state (pressed/not pressed) results in the light turning on ?
b. What is the total current (calculate this theoretically) going through the button ?
c. What is the default state of the light (on/off) ?
Draw the circuit if you swapped the output circuit from one of the circuits to the other
a. Would the light still work ? (note: look at the voltage across the output circuit)
remember: when the LED is on, there is a fixed voltage drop across it.
b. What if the value of R1 is very low, say 100 ohms ? (note: do not build this
circuit)