Procedure: Determine the polarity of the LED. Use the following image to help:

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1 Section 2: Lab Activity Section 2.1 Getting started: LED Blink Purpose: To understand how to upload a program to the Arduino and to understand the function of each line of code in a simple program. This is a standard simple first step into using the Arduino IDE. For a quick refresh on the Arduino environment refer to the Arduino help page on the IDE. Terms: Digital output: a zero or a one (high or low voltage) on a specified pin of a microcontroller. LED (Light Emitting Diode): a semiconductor light source. When biased with the correct voltage the LED emits light. NOTE: LEDs are polarized. Polarized: for electrical components polarization refers the assignment of a sign to a given terminal of a device (it matter what side is connected to power). If the polarity of a component is reversed (connecting terminals backwards) it may break. Sketch: the name that Arduino uses for a code file. Note that Arduino code sketches are stored as.ino files in the Arduino file under Documents. Materials: Arduino Board LED (color of your choice) 220 ohm resistor (red red brown) USB A-B cable Procedure: Determine the polarity of the LED. Use the following image to help: Figure source:

2 On an LED, the anode is the positive terminal (long leg) and the cathode is the negative terminal (short leg). Make the circuit. In the figure below, D13 is digital pin 13 of the Arduino. Use your knowledge of the Arduino board established in the pre-lab to find this pin and your knowledge from electronics section of BME 201 to create the circuit below: Figure source: An LED should ALWAYS be used with a resistor in series. See lab lecture 1 for information as to why this is needed. Check with an SA to assure your circuit is correct. Open Arduino IDE The application is found under the list of programs in the start menu or else should be found on your desktop.

3 Figure Icon of Arduino Application The Arduino application will open as seen in figure below: Figure Arduino Application Click on the open button in the toolbar Figure Open Button Hover over 01.Basics -> Blink and click on Blink to open the example.

4 Figure Path to open Blink example The following code will be loaded into the IDE: Listing 2.1 A /* Blink Turns on an LED on for one second, then off for one second, repeatedly. This example code is in the public domain. */ // Pin 13 ha s an LED connected on most Arduino boards. // give it a name: int led = 13; // the setup routine runs once when you press reset: void setup() { // initialize the digital pin as an output. pinmode(led, OUTPUT); } // the loop routine runs over and over again forever: void loop() { digitalwrite(led, HIGH); // turn the LED on (HIGH is the voltage level) delay(1000); // wait for a second digitalwrite(led, LOW); // turn the LED off by making the voltage LOW delay(1000); // wait for a second } Listing 2.1 A

5 Understanding the code Note the comment section at the beginning of the code that describes what the program does, what each variable means, and a general delineation of the algorithm. Refer to section 1.4 on programming practices. The Arduino IDE automatically color coordinates code based on its purpose or type. Note the different colors and when they are used to gain insight into the function of a statement. Lets start with the first statement that is not a comment: int led = 13; This line initializes a new variable named led. The variable is of the data type int (an integer) and has the value of the number 13. This is a variable declarations as described in the variable section above. Note that this statement is not within any of the following methods. Can you guess why this is the case? Explain. Check out this link to a reference page on the Arduino website on variable scope. Next is a function declaration: void setup() { This function has a return type of void meaning that when it finishes running, there is no value that is returned to the calling function. Review the reference information in the Section of syntax for more information about return types but for now this is not totally essential to understand. The setup function called first every time a sketch runs. This function runs only once and is used to initialize variables, set pin modes and several other single iteration tasks. Note that at the end of the setup function declaration there is an open bracket {. This indicates that the function is open and all the information up until the second and opposite closing bracket } is inside the setup function. Remember that a function can be identified by the parentheses () after its name. Within the setup function the pin used for the led is initialized as an output pin (so that signals can be sent from the microcontroller to the pin): // initialize the digital pin as an output. pinmode(led, OUTPUT); Note that pinmode is a function that takes two parameters, namely an int that corresponds to a pin and a keyword (OUTPUT in this

6 case) to specify the function of a given pin. Read more about this function on the Arduino Reference page for pinmode. Note the closing of the setup function with the } under the pinmode function call. Next is another function declaration: // the loop routine runs over and over again forever: void loop() { This function also has a void return type. The loop function, predictably, loops consecutively. This means that the code starts execution at the top of the file, runs through the setup function, then gets to the loop function. The code in the loop function will run once, then immediately start the loop function again and continue to do so FOREVER. Recall the discussion of infinite loops in the prelab. Explain why it is an important that the loop runs infinitely and predict some problems this may cause. Then the LED state is changed using the digitalwrite function // turn the LED on (HIGH is the voltage level) digitalwrite(led, HIGH); The digitalwrite function has a void return and is used to change the digital logic state of a pin. In this case the led pin (called led ) is changed to the value of HIGH. This will cause the LED to turn on. When the led pin ( led variable) is set to a HIGH state by the digital write function, the voltage of the pin on the microcontroller associated with led (pin 13) is pushed to a high voltage. This powers the led in the circuit and light will turn on. A delay is used to set how long the led will stay on. // wait for a second delay(1000); The delay function will pause most operations on the processor for the specified number of milliseconds (1000 milliseconds = 1 second). Delay effectively stops execution of the program. It is good practice to avoid the usage of the delay function as completely pausing the execution of the program is inefficient and can cause issues in more complex programs. Finally the led is turned off and there is another delay so that the led is off for one second: // turn the LED off by making the voltage LOW digitalwrite(led, LOW);

7 // wait for a second delay(1000); These two function calls complete the blink method by turning the led off again. This time the digitalwrite function sets the value of the led to low. Effectively turning off the led. Finally a delay is used to keep the led off for one second. Note the closing of the loop function with the } under the delay function call. This signifies the end of the loop method. NOTE that after the loop function has closed, it will immediately begin execution again at the top of the loop function again. This loop will continue to execute until a new program is uploaded or power is removed from the system. Congratulations! You have just read a computer program. Now it is time to test. Uploading code to Arduino Board: Verification: Before uploading the code to the microcontroller, verify that all the syntax is correct. To do this press the verify button on the toolbar the top of the Arduino window: Figure Note that any syntax errors will be highlighted and an error message will be displayed in the console and the bottom of the Arduino window: Figure The verify button is only used if you do not have an Arduino connected to the computer because the upload button (see next step) also conducts a code verification. Connect the Arduino Board Plug the Arduino board into the computer using the USB A to B cable (shown in figure below).

8 Figure : USB A to USB B cable. The USB B side will plug into the Arduino Board and the USB A side will plug into your computer. Use the tools dropdown menu from the toolbar and select board and the select Arduino Uno. (tools -> board -> Arduino Uno) Figure Use the same menu path to access the serial port configuration and select the COM port the Arduino is on. The Arduino should be on the only other port other than COM1. Ask an SA for help if you do not see your board. (Tools -> Serial Port -> COMX) Upload: Now that we have confirmed the code is free of syntax errors we will upload the sketch to the microcontroller. To upload simply press the upload button:

9 Figure Note the console above will display feedback showing that the sketch has been properly uploaded to the Arduino. Verify that the led connected to pin 13 is now turning on and off. If this is not working, check with a student assistant. How long does one blink cycle take (what is the period)? What is the frequency of this signal (Hz)? Utilize the oscilloscope to verify your reading. Have an SA verify this is correct. Section 2.2: Digital Input/Output As stated earlier, microcontrollers such as the Arduino are used to electronically interact with the environment. So far we have controlled an LED and implemented simple communication with a computer, but now we want to take input from the external environment and use it to perform some activity. Input is used to implement external control over a program. Output is used to show the progress or result of a program s execution. There are two types of input and output: digital and analog. This section will focus on digital. What does it mean to be a digital input? For a computer, it means an input that can be interpreted as a 1 or 0 (true or false, respectively). A 1 in software, or true, corresponds to a high voltage. Alternatively, a 0 in software, or false, corresponds to a low voltage in hardware. The high and low voltages are based on a given reference voltage that depends on the microcontroller being used but is most commonly 3.3V or 5V. Example: An Arduino has a reference voltage of 5V. Match the following input voltages with either a 1 (high voltage) or 0 (low voltage). 4.6 V == 1 (true) 0.9 V == 0 (false) *5.1 V == 1 (true) 1.1 V == 0 (false) *NOTE: A voltage higher than the reference voltage will still be read as a one; however, to avoid damaging the hardware try to avoid this situation. The example above clearly demonstrates the difference between high and low voltages with respect to a reference voltage. There exists a range of voltages in which

10 one cannot be sure if the hardware will read the voltage as a 1 or 0. This range is usually between about 1.5V and 3.5V, so when designing hardware that utilizes a digital signal be sure to keep low voltages as close to 0V as possible, and high voltages as close to 5V. Also, keep in mind that every microcontroller is different, so a range that works for one may not work for another one. Terms: Digital Input: A single input value that can be read as either a 1 or 0, corresponding to HIGH and LOW voltage. Digital Output: An output value written as either a 1 or 0, corresponding to HIGH and LOW voltage. Getting Started: For this portion of the lab we are going to turn an LED on and off when a button is pressed. The Arduino will be used to read the state of the button and control the led accordingly. What you ll need: One tactile switch (button) One 10kΩ resistor One 220Ω resistor One LED For this example, we will connect an LED to digital pin 13 on the Arduino. This pin will be used as our digital output to control the LED. The button will be connected to pin 12 on the Arduino. Pin 12 will be used as our digital input so we can read if the button has been pressed. A button should not be connected directly to the digital pin of the microcontroller. Instead, we are going to use a pull-down resistor to keep the input low (a logic 0 ) when the button is not pressed, and bring it high (a logic 1 ) when it is pressed. The resistor is used to limit current in the circuit and protect the microcontroller from being damaged. Also, pay attention to how you connect the button in the circuit and use Figure below to help.

11 Figure Once you have the circuit set up, have an SA come over and check your connections. Next, copy the code in Listing 2.2 A, compile it, and load it onto the Arduino. Listing 2.2 A ////////////////////////////////////////////////////////////////////// // Button Controlled LED - Digital I/O // Author: R Scott Carson // BME 201 // Spring 2014 ////////////////////////////////////////////////////////////////////// int button = 12; // Used to make p12 a digital input int LED = 13; // Used to amke p13 a digital output void setup() { // Initialize digital I/O pins pinmode(button, INPUT); // p12 is now an input pinmode(led, OUTPUT); // p13 is now an output } void loop() { // Here we check if the button is pressed using the // digitalread() function. if(digitalread(button) == 1){ digitalwrite(led, HIGH); // If it is pressed, turn on the LED } else{ digitalwrite(led, LOW); // Otherwise, turn off the LED } } Listing 2.2 A

12 The code in Listing X.x is not very complicated and only introduces a few new concepts. In the setup() function we need to initialize both an input pin and an output pin. This is extremely easy to do using Arduino s pinmode() function which has been explained before. Using this function, we set pin 12 to a digital input to read the button and pin 13 to a digital output to control the LED. In the loop() function we control whether the LED is on or off using an if/else statement. To read the state of the button we use the digitalread() function. All we have to do is give the function the pin we want to read and it will return a 0 if the pin has a low voltage or a 1 if the pin has a high voltage. If the button is pressed, the pin will have a high voltage, therefor digitalread() will return a 1. This would make the condition in the if statement true and the LED would be turned on using the digitalwrite() function. If the button is not pressed, the pin will have a low voltage and the digitalread() function will return a 0. In this case, the condition in the if statement would be false, and the LED would be turned off. Exercise: Now it is your turn to write some code. The goal of this exercise will be to use two push-buttons to control two different LEDs. All of the code you need for this has already been given to you in the example above, but it is up to you to piece it together correctly. Keep in mind that pins 3 13 can all be used for digital I/O. Do not be afraid to ask questions while building the circuit or writing the code. When you are finished, demo the working system for an SA.