3.1 Arduino Programs

3.2 Building Circuits & Kinds of Pins on the Arduino

Principle: In a circuit, electric current flows from higher potential locations to lower potential locations. Potential is measured in Volts (symbol V), relative to some ground point. This is similar to how we measure altitude. Altitude is your height in meters relative to the ground. But what we choose as ground depends on our needs. Airplane and mountain altitudes are measured relative to sea level. Parachutists measure altitude relative to the ground they are going to hit. The positive bus in our circuits is at +5 V compared to the ground at 0 V. In some circuits there are potentials below ground, in which case they will have negative voltages.

3.3 Part 1 - Blink the LED on Pin 13

1. Know how to start the Arduino environment, with a properly connected Arduino board.
2. Be able to enter in a program, compile it, and upload it to the Arduino board.
3. Know the parts of an Arduino program (called a sketch in the Arduino vernacular). A sketch is a program that has as a bare minimum two procedures named setup and loop.
4. Understand that the setup procedure is called once, and the loop procedure is called as often as possible. The moment that it returns it will be called again. Thus an Arduino program keeps running until you reset the computer.
5. Be able to write a program to manipulate the digital output pin 13 connected to the onboard LED.
   • Introduce an integer variable, named ledPin, and set it to an initial value.
   • Use a simple procedure (with no parameters or result) to perform an action. In general, a procedure may have parameters, and may return a result.
   • Use the pinMode procedure that sets the interface direction of a pin to INPUT (coming from outside the Arduino) or OUTPUT (going to outside the Arduino).
   • Use the digitalWrite procedure send a HIGH or LOW signal to a digital output pin.
   • Use the delay procedure to cause the Arduino to pause for a given number of milliseconds.
6. How to look up these details in the Arduino documentation.

1. Make sure the program is uploaded properly.
   1. Do the Tx and Rx LEDs flash during upload?
   2. Is the USB cable plugged in?
   3. Is the proper Serial Port selected in the Arduino IDE?
   4. Is the proper processor type (Mega 2560 or Uno) selected in the IDE under Board?
2. Hardware issues?
   1. Try pressing the RESET button on the blue circuit board.
   2. If not, try choosing new wires since it is possible that some may not work anymore.

Concept: A program is composed of different kinds of parts. Some parts are used to declare things, such as the name and type of a variable. Other parts perform actions, such as invoking the procedure that turns on the LED.

Concept: A variable is an item of data in a program. Most variables have names (or identifiers). Every variable has a value. As the program runs the value of a variable can change. Variables can store values that have a specific kind of types, for example integer or character.

A variable must be declared before the program can use it. The declaration gives: the name of the variable, its type, and possibly an initial value. For example, the statement int ledPin = 13; declares a variable called ledPin which is of type int (an integer number between -32768 and 32767), and gives it the initial value of 13, which indicates which pin the LED is hooked up to. The semi-colon (;) at the end is important because it signifies the end of the declaration.

Concept: We can take a sequence of program statements and place them into a named collection called a procedure. We can then perform these statements at a specific point in the program by using a procedure invocation. Procedures can have parameters and return a result. For example, the statement: digitalWrite(ledPin, LOW); invokes the digitalWrite procedure (that is defined elsewhere) with two parameters. Procedures can be identified by having two parentheses following the name of the procedure such as delay(). If a procedure requires parameters they are placed inside the parentheses, each one separated by a comma as shown with digitalWrite(). Procedures can also be called methods, functions or subroutines. The parameters are one way to pass information to the procedure, and the result is one way to get information out of the procedure. There are other ways.

The first parameter in the statement above is ledPin which says which digital I/O pin to use (recall that ledPin has a value of 13, the pin the LED is connected to), the second parameter is LOW which means the low output value. The result is to set the output of the pin to the LOW value. The procedure does not return a result.

3.4 Part 2 - Build a circuit with an external LED

1. Be able to interpret a simple circuit diagram and build it on the breadboard.
2. Be able to perform simple trouble diagnosis and correction when things do not go right.

1. The longer LED lead is the positive, so it goes to the wire and short lead goes to the resistor. The wire goes to Pin 13.
2. Remember to use the 'Green-Blue-Brown' resistor for the LED!
3. Looking for more information on the LED and resistor?

Arduino Mega	Arduino Uno
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1. Make sure the program is uploaded properly.
2. Make sure you have the proper wiring:
   1. Arduino 5 V to Left + on breadboard?
   2. Arduino GND to Left - (GND) on breadboard?
   3. Arduino Pin 13 to the breadboard row 1, left side of the division? (BB Left 01?)
   4. Make sure the LED is connected correctly. Long leg to + and short leg to the resistor.
   5. Resistor to row 2, left side of the breadboard and to the column of ground pins on the left side as well? (BB Left 2 to BB Left GND?)

Principle: The amount of current flowing in a circuit is measured in Amps (symbol A). Current, voltage, and resistance are related by the relationship E = I R where E is the potential difference measured in Volts, I is the current measured in Amps, and R is the resistance measured in Ohms.

• The first is that a LED has a strongly preferred direction in which it will let current flow. If you do not connect the LED properly it will not work. The convention is that the anode which is the longer lead, or the lead that does not have the flat side of the case is the one that connects to the positive potential. The cathode is the shorter lead, or the lead on the flat side of the case is the one that connects to negative potential.
• The second is that you must have a current limiting resistor in the LED circuit path. If not, the LED will burn out instantly.

Reality Check: In our circuit, the voltage E is 5V, the resistance R is 560 Ω, and so the current I is 5 / 560 = 0.009 A. Or, since we typically have small currents in our circuits, the current is 9 mA (milli Amps). Why do we have a resister in series with the LED? The resistance of the LED when it turns on is very small, so without a resistor the current that flows is large, and the resulting energy will burn out the LED. A typical LED should not have a current above 20 mA. So 9mA with our resistor is safe.

3.5 Part 3 - The Potentiometer

1. Understand how a potentiometer combined with analog input can be used for input.
2. Understand the relationship between what the program is doing, and when it can interact with the environment.
3. Be aware of interactions between your visual system and how you perceive output lights.

Concept: A potentiometer is a special kind of resistor. It has three pins. The outer pins are connected to the ends of the resistor. The middle pin is connected to a slider that moves between the ends of the resistor. If the outer pins are connected between +5 V and 0 V (GND), then the voltage on the middle pin will vary between 5 and 0 V, depending on whether it is closer to the 5V end or closer to the 0 end.

Arduino Mega	Arduino Uno
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Concept: A procedure invocation can return a result. This result can appear in a statement. For example, the statement delayTime = analogRead(analogInPin); invokes the analogRead procedure on the pin whose number is the value in variable analogInPin. It returns the result (an integer from 0 to 1023) and this is then stored in the variable delayTime.

1. When you turn the potentiometer in one direction the speed of the flasshing goes up, and in the opposite direction the speed goes down. How do the power (red) and ground (black) connections on the potentiometer relate to the direction necessary to increase the flashing rate?

2. When you turn the potentiometer to speed up the flashing rate, the LED appears to stop flashing. Then it suddenly gets dim. What is happening?

3. When you turn the potentiometer, the flashing speed does not change immediately. Why is this happening?

3.6 Part 4 - The Pushbutton

Concept: If a digital input pin is not connected to anything, it is said to be floating. Reading from a floating pin is very unreliable. It might be HIGH, but can be LOW. So to ensure that a proper voltage is always present on a digital input, a pullup circuit is used. The resistor attached to the pin is called a pull up resistor. It's job is to ensure that the digital input pin has 5V present when the switch is open. Then when the switch is closed it pulls down the voltage to 0V. You can install the pull up resistor yourself. But this is such a common issue that the Arduino processor has built in pull up resistors that can be turned on. This is done in the setup code of the program.

Arduino Mega	Arduino Uno
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Fritzing	Schematic
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1. Make sure the proper program is uploaded properly.
2. Make sure you have the proper wiring:
   1. The switch should have the pins coming out of the left and right sides, not the top and bottom when properly placed on the breadboard.
   2. A way to test this is to place the pushbutton on the breadboard just as shown in the wiring diagrams. Only when the pushbutton is placed correctly will it span over the gap easily between the division of the two halves of the breadboard.

Concept: The if statement is used to make decisions, and change the behaviour of a program. The if statement comes in two forms

if ( logical expression ) {
    block of statements to perform when logical expression is true
}
else {
    block of statements to perform when logical expression is false
}

or if there is nothing to be done in the false case:

if ( logical expression ) {
    block of statements to perform when logical expression is true
}
Almost anything that is proper code can appear inside the block of statements, including additional conditional statements. This is called nesting and it is very important when you only need the first condition to be true and other times you need the first condition and an additional condition to both be true. This will become important in another lab.

Concept Logical expressions are typically comparisons, like

• equal ==,
• not equal !=,
• less than <,
• less than or equal <=,
• greater than >,
• greater than or equal >=

or expressions that result from combining comparisons using the logical operations of AND, OR, and NOT which you may or may not have seen before. The code below demonstrates how conditional statements can used. Here we used a conditional statement to turn the LED light on when the button is pressed: if ( buttonValue == LOW ) Otherwise, else, we know the button is not pressed and the lightState (LED) is LOW (stays off).

Reality Check: Because a switch is mechanical, it takes time to open or close. In addition, when it is making this transition it behaves in an unexpected way: the mechanical contacts bounce for a while EC_3.8 very short (less than a microsecond) or long (fractions of a second). What this means is that we can't reliably trust a simple digital input from a switch. We have to wait long enough to assure ourselves that the switch really has changed state. For more details, see http://en.wikipedia.org/wiki/Contact_bounce, and a fascinating article (to some) on bounce characteristics, http://www.ganssle.com/debouncing.htm. We will revisit this later when we work with the pushbutton again in the second lab.

3.7 Part 5 - Sending Morse Code With the Button

• the dot (.) and
• the dash (-) which is 3 times as long as a dot, and
• the gap (of no signal). The gap comes in three lengths:
  • an inter-element gap between parts of a letter of duration same as a dot
  • a short gap between letters of 3 dot duration,
  • and a medium gap between words of 7 dot duration.

3.8 Part 6 - Sending SOS With a Program

3.9 Part 7 - Using Procedures to Reuse Code

1. Be able to take sequences of statements that are repeated and collect them into a procedure.
2. Take code (to set the dot length by reading the potentionmeter) from a previous program and reuse it in a new program.

• Complete the code for sendDot and sendMediumGap.
• Complete the code to send out SOS. The code sample only sends an O.
• Add code to read the potentiometer and set the dot length.

• Why doesn't the program read the button?
• Why doesn't the second push of the button turn off the beacon?
• Fix these problems!
• Even when you fix the turn off problem, the pushbutton has to be held for some time, why?
• How could you get around that problem. (One solution is called polling).

3.10 Other Things to Do

• You will need a new variable to read the pushbutton. You can call it buttonValue and you can declare it at the beginning of the code along with the other variables like dotTime.
• You will need to consider two states. One is when the SOS signal is being transmitted and one when it is not. Hint: You can use conditional statements to help.

• Why doesn't the program read the button?
• Why doesn't the second push of the button turn off the beacon?
• Fix these problems!
• Even when you fix the turn off problem, the pushbutton has to be held for some time, why?
• How could you get around that problem. (One solution is called polling).

• Add a second LED of a different color that is on when the original LED is off, and off when the original led is on.

• Add some additional LEDs and make them flash in sequence. That is, is you had three LEDs then they would start off as ON OFF OFF, then go to OFF ON OFF, then to OFF OFF ON, and then back to the beginning of ON OFF OFF

• Do the previous thing, but have them change state when you push the button.

• Something else interesting. For example, having the 3 LEDs blink starting at one end, to the other, and then back again. (100 010 001 010 100...)

3. Introductory Lab - Flashing Lights and Morse Code Arduino Intro Labs for Tangible Computing / Version 1.00 2012-09-24