Prototyping with Microcontrollers, Sensors, and Materials

Objective

The objective of this lab is to utilize electronic components, an Arduino board, and the Arduino IDE (Integrated Development Environment) to control an LED without and with a button, to take temperature readings, and to design a prototype for a product. The Arduino IDE will be used to program the Arduino board.

The prototyping will focus on designing and building a thermal insulation device that will be tested and the resulting data analyzed. All designs will be tested for their capacity to slow the rate of heat loss from melted wax placed inside them. The design will be entered in a competition that will be judged by a ratio that uses the cost of the device, its insulating capacity, the final temperature of the melted wax inside the device, and the room temperature. The lowest ratio wins.

Overview

Prototyping

Prototyping is the process of designing and building an early model of a product to test a concept or process. Any system or device that will be sold to consumers, government agencies, or businesses will begin as a prototype that typically does not have all of the components or functions that will be used in the product that is eventually brought to market. A prototype can serve as a proof of concept showing that the system or device can be built and will perform correctly. In this lab, a prototype of a thermal insulation device will be built. Its function will be to reduce the rate of heat loss from a container of heated wax placed in the device. The prototype insulating device will use a thermistor to measure heat loss and it will be operated by a microcontroller.

Electricity

Electricity is the movement of electrons. Electrons flow through a conductive wire when there is a difference in charge between two points in the wire. This flow of electrons is the electrical current and it is measured in amperes (A). Due to convection, electrical current flows in the opposite direction of the electrons. The difference in charge is the electrical voltage and is measured in volts (V). Certain materials resist that flow of electrons. This property is electrical resistance and is measured in ohms (Ω). Ohm’s Law (1) describes the relationship of the voltage across a resistor, the current (I) flowing through a resistor, and the resistance (R) of the resistor.

$V=I*R$

(1)

Variations in voltage and current are also used in digital signal processing to operate complex systems and devices and simpler devices, such as microcontrollers and household digital instruments.

Electronic Components

Several basic electronic components are used to build simple circuits. Some of these components are polarized, which means the way they are connected affects their functionality.

DC (Direct Current) Voltage Sources

DC voltage sources are used to power circuits because they have a voltage difference across their terminals. DC voltage sources are usually batteries (e.g. AA, AAA). Arduino boards can be powered by a battery, a USB cable, or an AC adapter. When the Arduino is powered, it can be used as a 5V DC voltage source. They are polarized.

Resistors

Resistors (Figure 1) are components that reduce the current flowing through a circuit and convert the excess current to thermal energy. Resistors can be used to control the voltage and current of circuits. Resistors are color coded to indicate their resistance (Figure 2). They are not polarized.

File:Resistor.jpg

Figure 1: Symbol for a Resistor

Figure 2: Resistor Color Codes

A thermistor (Figure 3) is a thermal resistor that is used to measure temperature. The voltage in the thermistor will change proportionally to the temperature. The output voltage can then be converted to a temperature reading.

Figure 3: Thermistor

Push-Buttons and Switches

Push-buttons and switches (Figure 4) are mechanical devices that interrupt or divert current. Basic push-buttons are polarized while basic switches are not.

File:Button switch.jpg

Figure 4: Symbols for Buttons and Switches

Diodes and Transistors (BJT/MOSFETs)

Diodes and transistors (Figure 5) allow current to only pass in one direction. MOSFETs are electrically controlled switches. They can also be used to amplify signals. They are polarized.

Figure 5: Symbols for Diodes and Transistors

Light Emitting Diodes

Light emitting diodes (LEDs) are small electric lights that use low voltage and current (Figure 6). The orientation of an LED is important since it acts like a diode and only allows current to flow in one direction. Most LEDs also require a resistor (typically 470 Ω) in series because they will burn out almost instantly when they encounter high current. They are polarized.

Figure 6: Symbol for an LED

Microcontrollers

A microcontroller is an inexpensive, programmable computer without any peripherals, such as a mouse, keyboard, or screen. Microcontroller boards have direct access to the input and output pins of their processing chips so that the user can directly read from sensors and perform actions. Microcontrollers are used in many electrical appliances, such as microwaves. Arduino boards (Figure 7), which use a microcontroller, were designed to be easily programmed and assembled into larger projects. These boards come in many shapes and sizes and some contain additional features, such as WiFi or Bluetooth connectivity. Different boards can also have different features, such as processing speed and memory size.

Figure 7: Arduino UNO

This lab will use an Arduino UNO board created by SparkFun called a RedBoard (Figure 8). A RedBoard has many of the basic functions of a computer.

Figure 8: RedBoard

Arduino Hardware

All Arduino boards have a general layout similar to that in Figure 9. Not all the sections and pins will be used in this lab or for the SLDPs.

Figure 9: RedBoard Layout

• Reset Button: Restarts the board
• USB Connector: Provides power and connects it to the computer
• Pin 13 LED: Usable LED without making an LED circuit
  
• Serial LEDS: Shows if the Arduino is transmitting or receiving data from pins 0, 1, or the USB connection

The power pins are used to supply voltage to other pins, and where pins can be grounded (Figure 10).

Figure 10: RedBoard Power Pins

• 3.3V: Usually used to power low-voltage sensors
• 5V: Most common power pin used to power circuits
• GND: Ground pin, which is 0V
• VIN: Voltage-in can be used to power the board using a battery or other external voltage source

The digital and analog pins are used for input and output commands to the microcontroller and electrical components (Figure 11). They can be used with both analog and digital devices, as the Arduino board converts analog inputs to a digital input.

Figure 11: Digital and Analog Pins

• A0-A5: Identical analog pins that can be used to read sensors or control analog devices. Pins A0-A3 are more stable than A4 and A5
• Pins 0-1: Transmitter and receiver pins. Do not use these pins for this lab
• Pins 2-12: Digital pins that can be switched between HIGH states and LOW states
• Pin 13: Connected to the onboard LED, use it only as an input pin

The Arduino IDE

The Arduino IDE is a program that can be used to edit, compile, and upload code to a supported microcontroller. Figure 6 is a screenshot of the program:

Figure 6: Arduino IDE screenshot

Verify: checks code for errors and points to where the errors occurred after it finishes. Upload: verifies code and then uploads it to the Arduino board if there are no errors.
Console: shows any errors the software found in hardware.
Serial Monitor: a tool used to see how a program is running. It’s like a multimeter for the program. Programs written in Arduino are called sketches. A basic sketch can be broken up into 3 different areas: global, setup and loop; these areas are pictured below.

Figure 7: Different areas

Global: constants and imported libraries go here.
Setup: activate the pins and sensors used. This code only runs once.
Loop: the code that runs continuously such as reading sensors and turning pins HIGH or LOW.

Arduino Programming

The Arduino programming language is based on C/C++, but it is designed to be simpler and easier to learn. The most intuitive way to think about programming is like building with LEGO blocks: certain rules must be followed and different building blocks can be used to build bigger parts. General

• Every line must either end with a semicolon ‘;’ unless it’s a conditional, loop, or function
• Comments start with a //
  • Comments are text that the program ignores
  • Used to label and explain code

Datatypes Datatypes are the different kinds of data values that can be used, manipulated and stored using C++. The table below includes the most basic and widely used datatypes.

Datatype	What it stores (examples)	Default value	Notes
Boolean	A true value (1, TRUE, HIGH) or a false value (0, FALSE, LOW)	0, FALSE, LOW	-
int	An integer number (-5, 15, 1047, etc.)	0	Can be positive or negative
double	A decimal number (-0.5, 123.77, etc.)	0	Can be positive or negative
char	A single character (‘c’, ‘A’, ‘5’, ‘?’, etc.)	Indeterminate	Must be enclosed in single quotes
string	A sequence of characters (“Hello World!”, “10”, “157+5”, etc.)	Empty (“”)	Must be enclosed in double quotes

Operators Operators perform operations on variables and constants. The results of these operations are usually stored in a variable. The table below includes common operators.

Operator	What it does	Notes
=	Assigns a value to a variable
+	Adds two or more values
-	Subtracts two or more values
*	Multiplies two or more values
/	Divides two or more values
++	Increment by 1	Usually used in loops
--	Decrement by 1	Usually used in loops
==	Checks if two value are equal	Usually used in conditionals
!=	Checks if two value are not equal	Usually used in conditionals
> or <	Less than/Greater than comparison	Usually used in conditionals
<= or >=	Less than/greater than or equal to comparison	Usually used in conditionals
&& or ||	Boolean AND or Boolean OR Used to cascade multiple Boolean operations	Usually used in conditionals

Constants and Variables Constants and variables hold data according to their datatype. They need to be given a name so they can be referred to later. Constants hold data that will NOT change while a program is running. Constants usually contain pin numbers or sensor threshold values. Variables contain data that WILL change while a program is running. Variables usually contain sensor values and other values that need to have mathematical operations done on them. Below is an example of how to create different constants and variables.

Figure 8: Constants and variables

Conditional Statements Conditional statements run code enclosed by their curly brackets when a condition is met.

Figure 9: Conditional statements

Loops Loops run the code enclosed by their curly brackets a specific amount of times or until a condition is met. While-loop While-loops are used to perform a task until a condition is met For-loop For-loops are used when you want something to run a specific number of times. Although they seem complicated at first, the structure of most for-loops is the same. In the parenthesis, the first part sets a variable (usually ‘i’ for ‘index’) to a value used to begin a count, the middle is the condition when the loop stops, and the third part is where you increment or decrement the counting variable.

Figure 10: While and for-loops

Commonly Used Arduino Functions

Function	What it does
pinMode(pin,mode)	Sets a pin as an input or output
digitalWrite(pin, value)	Sets a digital output pin to HIGH or LOW
digitalRead(pin)	Reads an digital input pin as HIGH or LOW
analogWrite(pin, value)	Sets an analog output pin to a value 0-1023
analogRead(pin)	Reads an analog output pin as a value 0-1023
delay(milliseconds)	Pauses the program for a certain amount of time
Serial.print(value)	Prints the value (variable) to the Serial Monitor.

Thermal Insulation

Heat is a form of energy. Heat transfer is thermal energy that is transferred from one body to another as a result of a temperature difference. Temperature is the measure of the average kinetic energy of atomic motion. The faster the atoms are moving, the higher the temperature.

The specific mechanisms that convey energy from one location to another are conduction, convection, and radiation.

When there is a temperature difference within a solid body or between two solid bodies in contact with each other, energy (heat) will flow from the region of higher temperature to the region of lower temperature. This is known as conduction.

Imagine a metal rod that is heated at one end. The atoms of the rod collide at the point where the temperature differs, transferring heat until the temperature of the rod becomes uniform.

Convection is the transfer of heat within a fluid medium (fluids consist of gasses and liquids). Convection can occur in two different ways. Convection occurs as natural and forced convection. Forced convection occurs when the main mechanism for heat transfer is due to the forced flow or motion of the fluid.

Figure 11: Air circulation diagram

Today we heat our homes through radiators using natural convection. Air flows through a heating element and then is dispersed through the room.

Suppose you wanted to disperse the heat even faster. In that case you could blow a fan past the heating elements. This is forced convection; it is one of the principles used in air conditioners to have a relatively small unit cool a large space.

According to the Encyclopedia Britannica, radiation is the process by which energy, in the form of electromagnetic radiation, is emitted by a heated surface in all directions. It does not require an intervening medium to carry it. The heating of the Earth by the Sun is an example of heat transfer by radiation.

Electromagnetic radiation is a mean of energy transfer that occurs when an atom absorbs energy. This EM wave can propagate as heat, light, ultraviolet, or other electromagnetic waves depending on the type of atom and the amount of energy absorbed.

Color is a property of light; when an object appears white, it virtually reflect all the EM waves coming to it while a "black" object absorbs it all. Therefore, color (reflectivity) is to be considered when choosing materials for thermal insulation.

Your container is a thermodynamic system – a part of the Universe separated from the surroundings by an imaginary boundary. There are three types of systems: open systems, closed systems and isolated systems.

Figure 12: Thermodynamic system with a boundary.

Open systems are systems where transfer of mass and heat is possible. For example, an open pot of boiling water is an open system – it exchanges heat with the air around it and water vapor. If collected, the water vapor can be condensed back to liquid water which has some mass.

Closed systems are systems where only heat can be transferred to the surroundings. A hermetically sealed bottle of soda is a closed system. If placed in a hot environment it absorbs energy in form of heat but the amount of liquid within does not change.

Isolated systems are systems which do not interact with the surroundings at all. No exchange is possible - neither heat nor mass. An ideal Thermos® is an isolated system. If hot chocolate is poured within, you will get the same amount back at the same temperature. No such system can be fabricated but can be approximated.

Now that we understand how heat is transferred, we must consider how to slow it down. Understanding how to minimize heat loss is the key to designing a successful insulating container.

The first consideration is the materials you choose. Using materials that are poor conductors of heat, like glass, will minimize heat loss.

Plastic is also a poor conductor of heat. Foam cups are made of plastic which have tiny air bubbles suspended in it. Air is among the poorest conductors of heat. A vacuum, or the complete lack of air, is the best insulator of all. This is the principle employed in the Thermos design.

The other important consideration in creating your container is its cost. Minimal design uses the fewest resources while maintaining the safety and efficacy of your product.

Thermocouples consist of two wires of dissimilar metals and are usually welded together or attached on a junction. When the temperature at a junction changes, it generates thermoelectric potential (emf) which is proportional to the temperature difference between the two junctions. This voltage difference can be used to measure the temperature at that junction.

Materials and Equipment

• Arduino UNO microcontroller and USB cable
• Computer with Arduino IDE
• Breadboard and jumper wire
• Resistors
  • 220 Ω
  • 2.2 kΩ
  • 10 kΩ
• Thermistor
• LED
• Pushbutton

Procedure

Starting a new sketch in Arduino

1. Open the Arduino IDE
2. Plug the Arduino/RedBoard into the computer
3. In the Arduino IDE toolbar, go to Tools > Board and select “Arduino/Genuino Uno”
4. From the Tools toolbar, select the correct port

Building Circuits on a Breadboard

Breadboards are small boards that are commonly used for circuit prototyping. They allow the connection of components that were discussed previously without making permanent connections.

Figure 13: Breadboard Connections

Activity 1: Building an LED Circuit

1. The first activity will be making a simple LED blinking circuit. The programming flowchart and circuit diagram are in Figure 14.

   

   Figure 14: LED Circuit Diagram and Flowchart

2. First, wire the LED to the breadboard like in Figure 15. Remember, since LEDs are polarized, their orientation matters. The shorter leg of the LED should be connected to the same row as GND. The resistor is NECESSARY, otherwise too much current would flow and the LED will burn out! Make sure to wire power to the power (red) rail and the signal from 7 to the LED directly

   

   Figure 15: Arduino Wiring

3. Now type the following code into a new sketch.

   

   Figure 16: LED Code

4. The flowchart uses Digital Pin 7 on the Arduino as an output. Therefore, create a constant that holds the number 7 and in the setup area set Pin 7 as an output using pinMode. Then, turn the LED on by using digitalWrite, have a delay of one second, turn the LED off by using digitalWrite and then set another delay of one second.
5. The LED circuit will be used in the next activity. Do not deconstruct it.

Activity 2: Using a Button

1. Activity 2 adds a button to the circuit from activity 1 and requires conditionals (think if-statement). The LED should be on when the button is pressed and off when the button isn’t pressed.
2. Before you breadboard the circuit look at the bottom side (pin side) of the button to examine which pins are connected.

There is a line connecting the pins that are wired together internally on each side. See the schematic below, pins 1 and 2 are connected, and pins 3 and 4 are connected. Make sure the button straddles the break in the breadboard

Figure 17: Button Circuit Diagram

1. First, breadboard the circuit diagram in Figure 18 and sketch a flowchart of the program needed. Have a TA verify the flowchart.

   

   Figure 18: Arduino Wiring

2. Write the Arduino program to implement the flowchart. Use an if statement
3. Remember to create a constant that holds the pin number to which the button is connected and that the button will be a digital input. After the button constant, create an integer that will hold the button state:

   

   Figure 19: Button integer

4. Within the loop function, you must check the state of the button (whether it is pressed or not pressed), using the following code:

   

   Figure 20: Button state

Activity 3: Prototyping a Thermal Insulation Device and Product Evaluation

Competition Rules

The following rules must be observed at all times during the competition. Violation of any of these rules will result in the disqualification.

• You must use a cup or clay in the design of your thermal insulation device
• In order to protect the wax from being ruined, no materials may be poured on top of the jar
• Students are not allowed change the placement of the thermistor with respect to the lid
• The container may not be held
• External heat sources are prohibited
• The candle must be inside the container within 30 seconds from when you receive it

Materials with Price List

• Large foam cup - $0.50
• Lid - $0.25
• Pack of clay - $0.20/bag
• Wool fabric pieces - $0.10/2 pieces
• Cotton balls - $0.05/3 pieces
• Popsicle sticks - $0.01/stick
• Paper cup - $0.40
• Styrofoam pieces - $0.05/3 pieces
• Tape - $0.10/ft
• Aluminum foil - $0.30/ft²
• Plastic wrap - $0.02/ft²

"NO RETURN" POLICY: When calculating cost, you must include ALL materials you request, even if you end up not using them. Make your selections carefully so you don't end up with cost that hurts your performance, but has no benefit.

Competition Procedure

Building a Thermistor

Using the Arduino, the temperature change of the candle will be recorded over the course of 15 minutes. The Arduino will read the temperature through the thermistor and print out the values into serial monitor.

Figure 21: Arduino thermistor wiring diagram.
1. Carefully remove the existing circuit, and wire the circuit according to the following configuration. A 10 KΩ (Brown, Black, Orange) resistor should be used. Make sure that pin A0 is used, and the circuit is powered to 5V and grounded.
2. Download the program here: https://drive.google.com/open?id=1XTx0EHq4knP3qQIawumjvxLWdxH4rp1T
There are missing components in the code; make sure to read through the comments and insert code where it is necessary. After the program is completed and uploaded, open up the Serial Monitor to check if the readings are correct (should be in the 70s °F range). Keep the circuit intact since it will be used to measure the temperature of your container.
3. Notes: A thermistor is a thermal resistor, which is a resistor that changes resistance with temperature. Depending on the temperature that it detects, the amount of voltage that goes through the thermistor will change proportionally to the temperature. Using the output voltage of the thermistor, it can be converted to a temperature reading. The Arduino should be taking a temperature reading every 5 seconds. The analog voltage value read through pin A0 should then be converted to a Fahrenheit reading. The temperature reading should be printed to the Serial monitor along with the seconds timestamp of the reading.

Insulating Container Design

1. Analyze your materials and consider your design options, keeping in mind the lab's specifications. Make sure you make preliminary sketches during this process.
2. Now, sketch your design. Label your drawings clearly. Prepare a price-list for your insulating container based on the materials you have chosen.
3. Build your insulating container based on the sketch you just completed. Your TA will provide the materials needed for your design. If you decide to modify your design during the construction of your insulating container, note the changes and describe the reasons for them. If the modifications required more materials to be used, make sure you update your price list and your TA approves it.

Competition

1. Have a TA test your Arduino code. Run the program for approximately 30 seconds to obtain an average room temperature. The data from the Arduino can be seen in the Serial Monitor on the top right corner of the Arduino IDE.
2. Stop the program after 30 seconds and check to ensure that the data was collected.
3. The TA will bring the candle to you once you are ready to receive it. Place the lid with the thermistor attached over the top of the wax. Be sure the top of the container is loosely covered with the lid.
4. Do not adjust the thermistor from its position in the lid.
5. Do not screw on the lid; just place it over the container.
Warning: Be careful! The hot melted wax is HOT!
6. Restart your Arduino program. Once the temperature readings stop increasing, start timing your 15 minute run.
7. The data from the thermistor will allow for further analysis. The Arduino data from the Serial Monitor will be used to attain the IC for the competition calculation. PLEASE DO NOT CLOSE OUT OF THE SERIAL MONITOR WINDOW. After 15 minutes (or 900 seconds), copy the data from the serial monitor into an Excel file.

Data Analysis

1. The data pasted from the Serial Monitor into Excel is not correctly separated into columns; therefore, to put them in the correct format, highlight all the data, and go to Data -> Text to Columns -> Delimited, and check off comma. Press finish to see the data in the correct columns.
2. Create a graph using the X, Y Scatter template. You'll find the template on the Insert tab, under the Charts group, with the Scatter icon. Click on the arrow below the icon and select the top left icon in the pulldown gallery. You can get the axes you want by clicking on the axis. You can get labels and titles by clicking on the chart, which will change the ribbon to the Design tab. In the Charts Layout group, click the icon that looks like the chart you want. Right click on the things you want to change.
3. For the thermistor name the X-axis Time, name the Y-axis Temperature. Plot it in half minute intervals for fifteen minutes, starting from the downhill trend. You may need to divide the Arduino data by 60 to convert to minutes. You may select the intervals based on your results. When you are finished, your graph should look similar to Figure 22.

Figure 22: Temperature vs. Time diagram of first 15 minutes of VI run
4. Calculate the Insulating Capacity (IC) of your design, do not include the first few seconds of an uphill trend, this is just the thermistor changing from room temperature to the temperature of the wax. IC The IC is the value of the slope of the graph of fifteen minutes of data. The IC is calculated using the data from the Arduino for this lab.
5. Add a trendline to your graph. To do so, click on the chart to get the Design tab on the ribbon. Under the Chart Layouts group, click on the chart template that has a trend line. As before, right click on the various items to make them what you want, including deleting things. Finally, right click on the trend line. This will bring up the Format Trendline window. On the left side, the Trendline Options item should be highlighted. If it isn't, click on it to highlight it. On the right side near the bottom is an item Display Equation on chart. Click on the check box to the left of this item and click Close. You can then click on the equation that's on the chart to move it where you want.
6. Calculate the Minimal Design Ratio (MDR) for your design:
$MDR=\left|IC\right|\times cost\times {\frac {T_{\text{R}}}{T_{\text{F}}}}\,$ IC is the insulating capacity you calculated earlier. Cost is the cost of your container, T_R is the temperature of the room given to you by the TA, and T_F is the final temperature read by the thermistor. Check the MDR using data from all the devices for a better reference. Again, please use IC from Arduino to calculate the final MDR.

Note: If your average room temperature is significantly different from the TA's average, let the TA know.

The team with the lowest MDR wins.

Your lab work is now complete. Please clean up your workstation. Return all unused materials to your TA.

Assignment

Individual Lab Report

Follow the lab report guidelines laid out in the page called Specifications for Writing Your Lab Reports in the Technical Communication section of this manual. As you write, the following discussion points should be addressed in the appropriate section of your lab report:

• Describe the basics of Arduino and its application
• Explain heat, heat transfer and all the mechanisms that perform heat transfer. Discuss which of these mechanisms applied to your design
• Define what thermal insulation is and the different types of thermodynamic systems
• Discuss minimal design and its importance
• Describe your container's design. Explain the choices you made. Make sure you include a discussion of the materials you chose and why. Talk about your team's strategy for winning the competition
• What changes would have increased/decreased your MDR or IC?
• How did your team derive the IC value?
• Should the Temperature vs. Time graph be smooth or should it have spikes? Explain how closely your curve approximates the ideal and what would affect the readings you recorded
• Describe how your design succeeded or failed. Discuss design improvements
• Include spreadsheet with every team's results. Describe the results and talk about other designs in the class

Note: It is not unusual to experience instrumentation errors in this lab, leading to incorrect temperatures being recorded. Be sure to read How to Handle Unusual Data in the online manual to learn how to handle this.

Remember: Lab notes must be taken. Experimental details are easily forgotten unless written down. EG1004 Lab Notes Paper can be downloaded and printed from the EG1004 Website. Use the lab notes to write the Procedure section of the lab report. At the end of each lab, a TA will scan the lab notes and upload them to the Lab Documents section of the EG1004 Website. One point of extra credit is awarded if the lab notes are attached at the end of the lab report. Keeping careful notes is an essential component of all scientific practice.

Team PowerPoint Presentation

Follow the presentation guidelines laid out in the page called EG1003 Lab Presentation Format in the Introduction to Technical Presentations section of this manual. When you are preparing your presentation, consider the following points:

• What is the importance of prototyping and using Arduino?
• What is the importance of minimal design?
• What is the importance of materials in prototyping?
• Why is it important in today's world to minimize heat loss?
• What is the importance of proper data collection method and automation?
• Is there any benefit to using one data collection method over the other?
• How would you improve your design?

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