ENGG1203: Introduction to Electrical and Electronic Engineering
Second Semester, 2015–16
Lab 6
Objective:
• Begin constructing circuits for your project.
• Experiment with basic operations of different input and output stages.
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1 Finding your lab partner
You will be working with a randomly assigned partner for this lab. To find your assigned lab
partner and the assigned table,
1. Log in to Moodle.
2. Select the assignment Lab 6 Partner
Please proceed to your assigned table.
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2 Basic Rube Goldberg Machine Step
Your final Rube Goldberg machine project will consist of a number of interconnected electronic
steps. Each step itself can be represented as an electronic system as we covered in class shown
in Figure 1. Each of them is consist of 3 stages: input, output, and an optional processing stage.
Figure 1: A generic model of an electronic system with input, process and output.
2.1 Switch + Solenoid There are many different input and output stages you may utilize in
your project. We will start with a simple one here. We will use a mechanical switch (Figure 3)
as an input. The output stage we will use is a solenoid (Figure 2). The solenoid provides a
source of lateral pull force – When there is no power, the shaft is extended by default; when
turned on, the shaft is pulled into the solenoid via the internal magnetic coil, and hence the
shape of a magnetic coil in the symbol.
(a) Photo
(b) Symbol
Figure 2: A solenoid.
ENGG1203: Introduction to Electrical and Electronic Engineering
Lab 6
switch
(a) Photo
(b) Symbol
Figure 3: A Switch
Now, take a solenoid, without connecting to anything else, measure the resistance between
the two terminals. Record this resistance below.
Rsolenoid =
2.2 Construct the circuit in Figure 4(a). Instead of breadboard, we will use a high-density foam
board to provide mechanical support for the circuit and to use heavy-duty terminal blocks for
connecting to the power supply. Your circuit should look like Figure 4(b).
(a) Schematics
(b) End Product
Figure 4: Simple step with switch and solenoid
Now,
• Turn off power supply OUTPUT
• Set the output of Channel 1 to 12 V and 2 A.
• Turn on the power supply OUTPUT.
Press and depress the switch to turn on/off the solenoid. When the solenoid is on, record the
following from the power supply reading:
CURRENT =
VOLTAGE =
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ENGG1203: Introduction to Electrical and Electronic Engineering
Lab 6
WARNING: Never keep the solenoid turned on continuously for more than 30 seconds.
2.3 Turn on Voltage We want to find the voltage at which the solenoid turns on.
1. Turn the VOLTAGE dial on the power supply so it shows 0V
2. Turn on the OUTPUT of the terminals
3. Keep the switch pressed, gradually turn up the voltage supply from 0V to 12V until the
solenoid turns on. Record the voltage (VT,solenoid ).
4. Release the switch
5. Turn off the OUTPUT
VT,solenoid =
Turn off the power supply when you have completed this part. The solenoid will be damaged
if you keep it turned on for a long time. So whenever you are working with it, make sure you
DO NOT turn it on for a long time.
2.4 Checkoff 1
Show your complete circuit to your TA and answer the following questions:
• What is the threshold voltage for turning on/off the solenoid?
• How do you measure the current running through the solenoid?
• What is the resistance of the solenoid?
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3 A Different Input, A Different Story
Instead of using a switch, most input stages rely on component that changes its resistance according to physical phenomenon. For example in the light tunnel, you have used a photodetector
that changes its resistance according to the amount of light shining on it. For these kinds of
input, we’ll use a potential divider circuit similar to last week.
To emulate the effect of such potential divider circuit, we’ll again be using a potentiometer
this week. However, unlike last time, a heavy-duty potentiometer is used. This heavy-duty
potentiometer allows higher power dissipation and is easier to control mechanically for your
project.
3.1 Connect the circuit shown in Figure 5(a). You should be able to build this circuit by reusing
the same foam board from the previous step. Make sure you disconnect the solenoid from
the circuit board.
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ENGG1203: Introduction to Electrical and Electronic Engineering
Lab 6
680 Ω
−
+
12V
+
Vout
−
(a) Schematics
(b) End Product
Figure 5: A simple potential divider circuit
Measure the voltage Vout . Verify the function of the potential divider circuit by turning the dial
on the potentiometer. What is the range of Vout ?
3.2 Turn the pot until Vout = VT,solenoid + 1 where VT,solenoid is the value you measured above.
At this voltage, the solenoid should turn on when connected. Keep the dial of the potentiometer untouched.
Construct the following circuit by attaching the solenoid to your circuit. Your result should look
like Figure 6(b).
680 Ω
−
+
12V
+
Vout
−
(a) Schematics
(b) End Product
Figure 6: Potential divider input connected directly to solenoid output.
Now, turn on the power supply, is the solenoid turned on? What is the value of Vout ?
Vout =
Turn the dial of the potentiometer up and down to see if it has any effect on the solenoid.
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ENGG1203: Introduction to Electrical and Electronic Engineering
Lab 6
3.3 Checkoff 2
Show to your TA your implementation as in Figure 6(b) and answer the following
questions:
• Are you able to turn on the solenoid? Why and why not?
• How does the output voltage change as you turn the dial?
• Based on your knowledge in loading effect, what do you think is the best way
to turn on the solenoid?
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4 Isolating Stages
One way to ensure the input output abstraction is not violated as we construct circuit is to
isolate the stages. There are many ways to isolate stages. Here, we will use a solid-state relay
for that purpose.
OUT+
IN+
IN-
SS-RELAY
(a) Photo
OUT-
(b) Symbol
Figure 7: Solid State Relay
A sold-state relay is shown in Figure 7(a). We will use the schematic symbol in Figure 7(b) in
this class. The function of a SS-RELAY is very simple: When the voltage around the two input
terminals (in+ and in-) is higher than a threshold value(VT,ssrelay ), the output terminals (out+
and out-) are connected like switch. It is called a “solid-state” switch because the switching
action is implemented electronically. No mechanical part is presented inside the SS-RELAY.
As a side note, similar components you may use in the project include magnetic reed switch
and relay. These components behave similarly to the SS-RELAY except mechanical switches are
used internally.
Using a SS-RELAY, extend your circuit from previous step to become the circuit in Figure 8(a).
Your final circuit should look similar to that in Figure 8(b).
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ENGG1203: Introduction to Electrical and Electronic Engineering
Lab 6
OUT+
IN+
12V
SS-RELAY
OUT-
-
solenoid
IN-
+
V pot
+
V sol
-
(a) Schematics
(b) End Product
Figure 8: A potential divider input stage connecting to solenoid output stage via a solid-state
relay.
4.1 Turn your dial on your potentiometer from one end to another end. Does it turn on/off the
solenoid?
Now, turn your potentiometer until the solenoid is off. Measure Vpot and Vsol .
Then, gradually turn the dial up until the solenoid is just turned on. Measure Vpot and Vsol
again. Define the voltage value of Vpot at this point as VT,ssrelay .
Solenoid State
Vpot
Vsol
off
on
VT,ssrelay =
4.2 Checkoff 3
Show to your TA your completed circuit with the SS-RELAY acting as an isolating
buffer and answer the following questions:
• Is VT,ssrelay = VT,solenoid ? Why or why not?
• When the solenoid is on, what is the voltage across the two terminals of the
solenoid?
• When the solenoid is on, what is the current drawing from the power supply?
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5 Optional Steps
Congratulations! You now possess the basic framework to construct complex Rube Goldberg
machine. You may mix and match many different input and output stages as you design your
project. Using the circuit above with the SS-RELAY, you will be able to replace the potentiometer with any input stages, and replace the solenoid with other output stages. You may
use your project materials to explore.
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