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EMS1EP Lecture 4 Intro to Programming Dr. Robert Ross.

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1 EMS1EP Lecture 4 Intro to Programming Dr. Robert Ross

2 Overview (what you should learn today) Number systems Bits, Bytes, Pins Hello World – Arduino style

3 Digital Revision – Number Systems Computers use binary (base 2 number system) Humans like to use decimal (base 10 number system) Hexadecimal (hex) is a nice way of displaying binary numbers Notations: – Binary: 01010010b or 01010010 2 – Decimal: 212 or 212 10 – Hex: 0x31 or 31h or 31 16 When you write code – the compiler doesn’t understand the subscript 2, 10 or 16, so just use the first notation

4 Bits and Bytes A Byte is a single binary digit – It can hold either a ‘0’ or a ‘1’ A Byte is a collection of 8 bits – e.g. 01001101 – In hexadecimal: 0x4D A normal DVD holds 4.7GB (GigaBytes) so it holds (1024 x 1024 x 1024 x 4.7) Bytes of data

5 Pins The microcontroller has many pins (legs) on it Most of these we can independently control (set HIGH/LOW or read the HIGH/LOW state) Some pins are used to supply power and a clock signal In contrast to ‘normal’ computer programming – here we are actually writing firmware to control and manipulate hardware at an electrical level

6 Programming intro Microcontrollers have many features: – Set pins high/low – Read if pins are high/low – Perform logical, arithmetic and timing operations The way we control and use these features is by writing code (programming)

7 Code 101 A program is made up of a series of instructions Executed sequentially Sample types of instructions – Arithmetic – Logical Comparisons – Controlling pins

8 Arduino IDE - Terminology Sketch – A program that you write setup() – Function run once when device started – used for initialisations loop() – Infinite loop function – runs forever Serial monitor Program device Verify (compile code)

9 Arduino IDE – Setting up Before code is run a few things need to be setup – Tools->Board->”Arduino Uno” – Tools->Serial Port-> What is the Arduino plugged into? Easiest way to determine this is to unplug the arduino and check the available ports Then plug the Arduino in and choose the new port that has appeared Free to download:

10 Arduino Hello World First program – write ‘Hello World’ to the screen Arduinos don’t have a screen They can send data in a serial format back to the PC – and the PC can display it on the screen (use the serial monitor option) Program purpose – send the message “Hello World” to the PC

11 Arduino Hello World // The setup() method runs once, when the sketch starts void setup() { // initialize the serial port interface (baud rate 9600bps) Serial.begin(9600); } // loop() method runs as infinite loop void loop() { //Send serial message Serial.print(“Hello World”); delay(1000); // Wait for a second }

12 LED Flasher for Arduino Another simple program that is often a first microcontroller program is flashing an LED on and off Need to set output of digital pin to high then low Delay in-between so doesn't flash too fast (8MHz)

13 Arduino LED Flasher // PIN ASSIGNMENTS int ledPin = 10; // LED connected to digital pin10 // The setup() method runs once on startup void setup() { // initialize pin as output: pinMode(ledPin, OUTPUT); } // Infinite loop void loop() { digitalWrite(ledPin, HIGH);// LED OFF delay(1000); // Wait 1S digitalWrite(ledPin, LOW); // LED ON delay(1000); // Wait 1S } Pin Declarations Setup Function Loop Function

14 Pin Declarations Global variables used to give names to specific pins Helps the programmer know what the pins are connected to If a red LED was connected to Pin 9: – int ledRedPin = 9; If a button to control an up counter was on Pin 12: – int buttonUpPin = 12; Pin Declarations Setup Function Loop Function

15 Setup Function The setup function is always run once at the start of the program This sets up the microcontroller – setting up pins (previously they were just defined), comms interfaces and timers void setup() { // initialize as output pinMode(ledPin, OUTPUT); } Pin Declarations Setup Function Loop Function

16 Loop Function This is a loop that runs directly after the setup() function This loop runs and repeats forever until you remove power to the Arduino Equivalent of a while(1) loop Other functions can be called from within this loop void loop() { digitalWrite(ledPin, HIGH); delay(1000); digitalWrite(ledPin, LOW); delay(1000); } Pin Declarations Setup Function Loop Function

17 delay() The Arduino board is operating at 16MHz If we flash an LED on and off at 16MHz it is much to fast for us to see Need to add delays to visibly see the LED turn on and off delay() is a millisecond delay function delay(1000) will delay for 1000ms or 1 second delay(5000) will delay for 5 seconds

18 Variables Variables are small chunks of memory where we can store data Variables have a name (generally something that describes its use e.g. ‘counter’) Variables have a type (describes how big the variables can be (e.g. Integer) Variables have a value e.g. counter = 5 Need to declare the variable before using it (this tells the compiler to save a small chuck of memory for this data)

19 Basics of control flow Most higher level languages have basic constructs for control flow (looping and decision making) – IF, WHILE, FOR, DO…WHILE Arduino is basically C code and so these still apply and are useful

20 Revision: If statement Allows you to do different things depending if a statement is true or false Syntax: if( ){ } else{ } Example: if(counter == 5){ counter = 0;//Set counter to zero } else{ counter = counter + 1; //Increment counter by 1 }

21 Revision: While Loop Keep looping while a conditional statement is true Syntax: while( ){ } Example: while(a > 5){ a = a + 1; }

22 Revision: For Loop Keep looping for a certain number of iterations Syntax: for(,, ){ } Example: for(j = 0; j < 10; j++){ //Do something } If j hasn’t been declared previously can do this: for(int j = 0; j < 10; j++){ Note j++ is the same as j=j+1

23 Bit Manipulations Some functions are available to allow individual bits to be read or written to: – bitRead(x, n); Returns the n th LSB bit of x If a = 201; –Z = bitRead(a, 0);//Returns 1 as bit 0 is 1 –Z = bitRead(a, 1);//Returns 0 as bit 1 is 0 – bitWrite(x, n, b); Writes a value (b = 0 or 1) to the n th LSB of x bitWrite(a, 1, 1); //Sets bit1 to high, now a = 203 Least Significant Bit (LSB)

24 Practice Programs Write a program that tests the variable ‘a’ if a > 92 then set it to zero, otherwise increment it by 2 Write a program using a while statement that loops 10 times

25 Summary (What you learnt in this session) Microcontrollers are small programmable devices we write code for to control things Arduinos are microcontrollers with lots of simple to use high level instructions The basics of programming

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