1. Week 4: Microcontrollers & Flow Control
Bryan Burlingame
13 Sept 2017

2. Announcements & The Plan for Today™
Homework #1 & #2 due up front
Homework #3
Discuss the flow control statements, if, for, & while
Discuss the Arduino and embedded systems
Read: finish chapter 5 & all of chapter 6 in the text
Had planned to talk about blocking and non-blocking code and debouncing switches.

3. Recall: Boolean Logic And && False True Exclusive Or (Xor) ^^ False

4. Numeric Comparison Operators ! (not) <, <=, >, >=
Changes true to false and false to true
<, <=, >, >=
Less than, and less than or equal to are different operations
Note: !(<) is the same as >=
==, != (not equal)
Note: equivalence uses a double ‘=‘, assignment uses a single ‘=‘, be wary
= returns the value being assigned
Technically, a = b = c = d = 5; is legal. Why?
= is performed right to left, so the d is assigned 5, which returns 5. That 5 is assigned to c

5. Examples
float b = 17.0; float d = 3.14; float c = 20.0; float e = 33.0; (b < c); //true (b + c); //true (not zero) ((int)(b/c)); //false (is zero, why?) (b < c) && (d > e); //false (b < c) || (d > e); // true (b < c) && (d > e) || (c < e); //true (b < c) && (d > e) || (b + c); //true, why? printf(“%f”, b) && (b + c); //true, why?

6. Flow control
These Boolean operations are used along with flow control (or branching) statements to control the flow of a program
Decisions
True
False

7. Flow control if/if else/else – do this, do that, or do the other
switch – choose between a bunch of items
for – Do something for some number of times
also commonly referred to as iteration i.e. iterating over a range or iterating over a data set
while – For as long as some decision is true, keep doing some stuff
do .. while – Do something. At the end, if some thing is true, do it again.

8. Selection Structure Overview
Three kinds of selections structures
if (also called, ‘single-selection’)
if condition is true
Perform action
if condition is false, action is skipped, program continues
if/else (also called, ‘double-selection’)
else (if condition is false)
Perform a different action (this will be skipped if condition is true)
switch (also called ‘multiple-selection’)
Allows selection among many actions depending on the integral value of a variable or expression

9. Single Selection IF - Flowchart
connector
flow line
action symbol
decision symbol
TRUE
Print “You’re speeding”
Speed > 65
FALSE
If the speed is greater than 65, take the action to print a message. If the speed is not greater than 65, just keep going on in the program.
What does Speed > 65 evaluate to if Speed == 72 ?
The symbol > is a Relational Operator. The Expression “speed > 65” evaluates to 1 if true, 0 if false

10. if - example
int speed = 5; int b = 4; if( speed > 65 ) { // do everything until the closing } printf( “You are speeding!\n” ); } // technically, when one statement is between // the curly braces, the braces are optional. // Even so, don’t omit them

11. Double-Selection IF - Flowchart
Print “Within speed limit”
Print “Over speed limit”
Speed > 65
FALSE
TRUE
Note that if Speed > 65 is true, then the message “Over speed limit is printed”, and then the program continues. If Speed > 65 is not true, then the message “Within limit” is printed.

12. if - example
int speed = 5; int b = 4; if( speed > 65 ) { // do everything until the closing } printf( “You are speeding!\n” ); } // technically, when one statement is between // the curly braces, the braces are optional. // Even so, don’t omit them else { // note the indentation. printf( “Speed is within legal limits\n” ); }

13. if - example
int speed = 5; int b = 4; if( speed > 65 ) { // do everything until the closing } printf( “You are speeding!\n” ); } // technically, when one statement is between // the curly braces, the braces are optional. // Even so, don’t omit them else if( speed < 65 ) { // note the indentation. printf( “Speed is within legal limits\n” ); } else { printf( “Speed is precisely 65\n” );

14. for Loop Structure – Flow Chart
initialization T F
Terminal decision
statement
Iteration
operation
Initializes the loop control variable:
ex. a = 0;
Tests the loop control variable to see if it is time to quit looping:
ex. a < 5;
Increments the loop control variable:
ex. ++a

15. for Loop Structure – Flow Chart
initialization T F
Terminal decision
statement
Iteration
operation
for( a = 0; a < 5; ++a )
{ //for( initialization, termination, iteration)
printf( “%d\n”, a ); }

16. while Loop - Flowchart View
Statement is executed while condition is true
Note that the condition must first be true in order for the statement to be executed even once
statement
TRUE
FALSE
condition

17. while Loop - Flowchart View
statement
TRUE
FALSE
condition
while( a < 5 ) {
printf( “%d\n”, a );
++a; }

18. What is a Microcontroller?
A small computer usually implemented on a single IC that contains a central processing unit (CPU), some memory, and peripheral devices such as counter/timers, analog-to-digital converters, serial communication hardware, etc.
ATmega328 the ‘brain’ of the Arduino

19. Where are Microcontrollers Used?
Everywhere!
Car
Phone
Toothbrush
Microwave oven
Copier
Television
PC keyboard
Appliances

20. The Arduino Platform http://arduino.cc/
USB jack
Microcontroller
power jack
Voltage regulator
Pwr/GND Pins
ICSP Header
Reset Button
Power LED
Pin 13 LED
Rx + Tx LEDs
Digital Pins
Atmel ATmega328 microcontroller
14 digital I/O pins
6 with PWM
6 analog I/O pins
32 kB (-2 kB) Flash memory
2 kB RAM
1 kB EEPROM
16 MHz clock
$22 - $30 built
$13 ‘breadboardable’
FTDI USB chip
Analog Pins

21. Fundamental Flow of an Arduino Program
Start
Setup
Loop
End

22. Programming the Arduino
/* Blue_LED_button_cntrl1 - turns on blue LED when SW0 on Experimenter board is pressed, off otherwise */
/* pin assignments */
const byte RGB_blue_pin = 6;
const byte SW0_pin = 12;
/* configure pins */
void setup() {
pinMode(RGB_blue_pin, OUTPUT);
pinMode(SW0_pin, INPUT_PULLUP); }
/* loop forever */
void loop()
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, HIGH);
else
digitalWrite(RGB_blue_pin, LOW);
An arduino program == ‘sketch’
Must have:
setup()
loop()
configures pin modes and registers
runs the main body of the program forever
like while(1) {…}
Where is main() ?
Arduino simplifies things
Does things for you
This slide is meant as a quick overview of an Arduino sketch. We’ll unpack and describe the pieces in more detail later.
Think of setup() as what you would do when you first get in a rental car or a car you have borrowed from a friend: adjust the mirrors, adjust the steering wheel, the seats, change the stereo channel settings, etc. The car can be driven by anyone, but everyone likes to customize it for their comfort.
main() {    init();    setup();    while (1)       loop(); } And the reason that they do it this way is so it's guaranteed that init() gets called, which is critical for Arduino initialization.

23. Using setup() A digital pin can either be an output or an input Output
const byte RGB_blue_pin = 6;
const byte SW0_pin = 12;
/* configure pins */
void setup() {
pinMode(RGB_blue_pin, OUTPUT);
pinMode(SW0_pin, INPUT_PULLUP); }
A digital pin can either be an output or an input
Output
your program determines what the voltage on a pin is (either 0V (LOW or logic 0) or 5V (HIGH or logic 1)
Information is sent out
Input
the world outside the microcontroller determines the voltage applied to the pin
Information is taken in
pinMode()
sets whether a pin is an input, input_pullup or an output
ledPin  byte constant assigned the value of 13
OUTPUT is a macro defined constant
Which has the value 1
INPUT is a macro …  ?
Emphasize that the distinction between inputs and outputs. As an example, you might have the class envision that the front row of students in the class are digital pins (everyone else are internals elements of the microcontroller). Designate one student as an OUTPUT. Have the rest of the students (in unison) tell the OUTPUT student to raise his or her hand. (Have the designated ‘OUTPUT’ follow the command!). Then have the rest of the class (in unison) tell the ‘OUTPUT’ to put his or her hand down. Thus, the microcontroller has sent information ‘out’, and the pin designated as an OUTPUT has responded accordingly.
Similarly designate one student in the front row as an INPUT. Have the rest of the class ask the INPUT student what the state of the room light is (is it on or off?). Have the INPUT student report to the rest of the class the state of the room light.
Explain the declaration of ledPin as a const byte variable. Explain the advantage over #define ledPin 13
Digital HIGH = = 5V (usually taken as logical 1) Digital LOW = = 0V (usually taken as logical 0)
wiring.h in arduino/hardware/cores/arduino #DEFINEs OUTPUT as 0x1 and INPUT as 0x0
where can you find out about the commands, etc?

24. Digital I/O Example - loop() Algorithm
Refine the pseudocode, cont.:
loop forever (use function loop())
If button is not pressed:
voltage on button pin 12 will be _______
make pin 6 voltage low (LED will go off or stay off)
If button is pressed:
make pin 6 voltage high (LED will go on or stay on)
high (5V)
low (0V)
void loop() {
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, HIGH); }
else
digitalWrite(RGB_blue_pin, LOW);

25. Digital I/O Example - Modification
/* Blue_LED_button_cntrl1 - turns on blue LED when SW0 on Experimenter board is pressed, off otherwise */
/* pin assignments */
const byte RGB_blue_pin = 6;
const byte SW0_pin = 12;
/* configure pins */
void setup() {
pinMode(RGB_blue_pin, OUTPUT);
pinMode(SW0_pin, INPUT_PULLUP); }
/* loop forever */
void loop()
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, HIGH);
else
digitalWrite(RGB_blue_pin, LOW);
Modify Arduino program, so that LED is on until button is pressed, then turns off
How?
Pin assignments?
setup()?
Need to turn on the LED!
loop()?
Swap values of second argument in digitalWrite calls
Pin assignments stay the same - no change to the external hardware or its connection to the Arduino
setup() - add a line to turn on the LED
loop() - swap the arguments in the digitalWrite() function calls: if button is pressed, then LOW, else, HIGH

26. Spartronics Experimenter Digital Pin Assignments13 12 11 10 9 8 7 6 5 4 3 2 1
SCK
MISO
MOSI SS
OC1
ICP
AIN1
AIN0 T1 T0
INT1
INT0
TXD
RXD
LED
pwm
LED0
LED1
LED2
LED3
green
blue
red
piezo
servo
SW0
SW1
SW2
SW3
Piezo rectangle is hyperlinked to an image of the actual Experimenter board. The piezo speaker is hyperlinked back to this slide.

27. Spartronics Experimenter Analog Pin Assignments7 6 5 4 3 2 1
photocell
POT
temp sensor
The rectangle around cells for pins 2, 1, 0 are hyperlinked to an image of the actual Experimenter board. Each respective element is hyperlinked back to this slide.

28. References
Modular Programming in C
math.h