Microcontroller Crash Course. Sam Fladung 7/30/2013

Transcription

1 Microcontroller Crash Course Sam Fladung 7/30/2013

2 What is a Microcontoller Processor + Peripherals Peripherals can include: Analog to Digital Converters (ADCs) Timers Serial Ports (UARTS) Synchronous Serial Ports (SPI/I2C) Pulse Width Modulation (PWM)

3 Course Outline Compile / Run a basic program Blink an LED (with sleep) Use timers to allow multitasking Functions State Machines and switch statement Other Peripherals

4 What this course will not cover In depth knowledge of C Program design / rules Multithreading RTOS Macros Microcontroller architectures

5 Basic Microcontroller Concepts Bit -> 1 or 0 (on/off) Byte (8 bits) -> 0:255 or -128:127 Register: A block of memory Special Function Register (sfr): A register that maps to some specific function Port (an SFR that connects to io pins) Endianness

6 Examples of Microcontrollers Atmel AVR (Arduino is based off these) Microchip PIC ST Micro STM32 Texas Instruments MSP430 Basic Stamp Many others

7 Related Technologies Digital Signal Processors (DSPs) Field Programmable Gate Arrays (FPGAs) Programmable Logic Controllers (PLCs) Embedded Computers (Raspberry PI, BeagleBone etc)

8 Programming Languages C by far the most common Provides good hardware access and bit manipulations Much better portability than Assembler Assembler Unique for each type of microcontroller Should generally only be used when speed/space optimization have a strong premium

9 Arduino Based on an AVR Microcontroller Onboard programmer Defined pinout Shields -> Expansion boards that plug into standard pinout Custom IDE/ Libraries with abstraction

10 Physical Setup Connecting up the boards to the computer USB Cable provides both signal and power to the board. Expansion cards may require additional power

11 IDE Setup

12 Basic c Intro Comments Any text after // is a comment Any text between /* and */ is a comment Assignment X=5; // x now contains the value 5 Comparisons 5==5; // True 5==4; // False 5<6; // True 5<5; // False 6>=6; // True 6>=7; // False

13 If statements in c Branching if (condition) do something ; else if(condition) do something ; else do something else ; By Default only the line after an if/else is included. For multiple lines, surround with curly brackets{ I recommend always including the brackets

14 A Note on Optimization Premature optimization is the root of all evil (or at least most of it) in programming. Donald Knuth Focus on making code understandable rather than worrying about optimizing IF you find a section is ACTUALLY slowing down your program to an unacceptable extent, then you can optimize.

15 Blinking an LED Board setup Port assignment: LED is Digital Port 13

16 Blinking an LED Source Code int led = 13; void setup() { pinmode(led, OUTPUT); // initialize the digital pin as an output. 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

17 Exercise 1 Type EX 1 code into your IDE, verify that it compiles and download to your Arduino Bonus Make the LED blink twice as fast Have LED be on for 1 second, but off for 10ms Send the message SOS in Morse code over the LED ( ) Pick a pattern and make the LED follow it

18 Using timers to avoid sleep Previous example works, BUT: Entire program blocks during sleep Can t do anything else while blinking the LED Use timers to know when to turn the LEDs on/ off

19 millis() function millis(): Returns the number of milliseconds since the Arduino board began running the current program. This number will overflow (go back to zero), after approximately 50 days.

20 LED blink with timers source const int ledpin = 13; // the number of the LED pin int ledstate = LOW; long previousmillis = 0; long interval = 1000; // ledstate used to set the LED // will store last time LED was updated // interval at which to blink (milliseconds) void setup() { pinmode(ledpin, OUTPUT); // set the digital pin as output:

21 LED blink with timers source (contd) void loop() { unsigned long currentmillis = millis(); if(currentmillis - previousmillis > interval) { previousmillis = currentmillis; if (ledstate == LOW) ledstate = HIGH; else ledstate = LOW; digitalwrite(ledpin, ledstate);

23 Creating functions Functions are portions of code that accept some number of argument and return a value They may or may not affect the underlying program state Functions allow code to be reused in multiple sections without copy and paste Functions allow code to be broken into multiple smaller chunks

24 Anatomy of a function int foo(int bar){ Return Type Function Name Argument Type Argument Name Special keyword void Scope Persistent (static variables)

25 Data Hiding / Encapsulation Limit which parts of the code can access variables Promotes clearer code Prevents unintended coupling Use static vars in a function rather than globals when the variable: is persistent Is only used in that function

26 Breaking the LED blink into a function void led_blink(void){ static int ledstate = LOW; // ledstate used to set the LED static long previousmillis = 0; // will store last time LED was updated unsigned long currentmillis = millis(); if(currentmillis - previousmillis > interval) { previousmillis = currentmillis; if (ledstate == LOW) ledstate = HIGH; else ledstate = LOW; digitalwrite(ledpin, ledstate);

27 Breaking the LED blink into a function (contd) const int ledpin = 13; // the number of the LED pin long interval = 1000; // interval at which to blink (milliseconds) void setup() { pinmode(ledpin, OUTPUT); void loop() { led_blink();

29 State Machine A state machine is used to perform different actions depending on the state of the system. State machines allow for effectively concurrent operations

30 Anatomy of a state machine States: Transitions State actions

31 Implementing a State machine with Switch Statements State variable Enums Switch statement switch(state_var){ case STATE_1: Do state actions Check if state should change state_var= NEW_STATE Case STATE_2

32 Implementing Different LED Blinks as State Diagram State Machine Time Expired Fast Blink Slow Blink Time Expired

33 LED State Machine Source Code const int ledpin = 13; // the number of the LED pin // Variables will change: int ledstate = LOW; // ledstate used to set the LED long previousmillis = 0; // will store last time LED was updated long previousmillisstate = 0; // will store last time State changed // the follow variables is a long because the time, measured in miliseconds, // will quickly become a bigger number than can be stored in an int. long interval = 1000; // interval at which to blink (milliseconds) long state_interval = 5000; // interval at which to blink (milliseconds) typedef enum {FAST, SLOW state_t; state_t state = SLOW; void setup() { // set the digital pin as output: pinmode(ledpin, OUTPUT);

34 LED State Machine Source Code(contd) void loop() { unsigned long currentmillis = millis(); switch(state){ case FAST: interval=200; if(currentmillis - previousmillisstate > state_interval) { previousmillisstate=currentmillis; state=slow; break; case SLOW: interval=1000; if(currentmillis - previousmillisstate > state_interval) { previousmillisstate=currentmillis; state=fast; break; if(currentmillis - previousmillis > interval) { previousmillis = currentmillis; if (ledstate == LOW) ledstate = HIGH; else ledstate = LOW; previousmillis=currentmillis; digitalwrite(ledpin, ledstate);

35 Exercise 4 Type EX 4 code into your IDE, verify that it compiles and download to your Arduino Bonus Rewrite state machine code to use functions Make the LED blink twice as fast Have LED be on for 1 second, but off for 10ms Send the message SOS in Morse code over the LED ( ) Pick a pattern and make the LED follow it

36 Expanding Your IO Options Serial Digital Input Analog Input

37 Serial Write void setup() { Serial.begin(9600); // initialize serial communication at 9600 bits per second: pinmode(pushbutton, INPUT); // make the pushbutton's pin an input: void loop() { // read the input pin: static int i = 0; Serial.println(i); i++ delay(1); // delay in between reads for stability

38 Serial Read int incomingbyte = 0; // for incoming serial data void setup() { Serial.begin(9600); // opens serial port, sets data rate to 9600 bps void loop() { // send data only when you receive data: if (Serial.available() > 0) { // read the incoming byte: incomingbyte = Serial.read(); // say what you got: Serial.print("I received: "); Serial.println(incomingByte, DEC);

39 Digital Inputs int pushbutton = 2; // digital pin 2 has a pushbutton attached to it. //Give it a name: void setup() { Serial.begin(9600); // initialize serial communication at 9600 bits per //second: pinmode(pushbutton, INPUT); // make the pushbutton's pin an //input: void loop() { int buttonstate = digitalread(pushbutton); // read the input pin: Serial.println(buttonState); // print out the state of the button: delay(1); // delay in between reads for stability

40 Analog Input void setup() { // initialize serial communication at 9600 bits per second: Serial.begin(9600); // the loop routine runs over and over again forever: void loop() { // read the input on analog pin 0: int sensorvalue = analogread(a0); // print out the value you read: Serial.println(sensorValue); delay(1); // delay in between reads for stability

41 Exercise 5 Type EX 5 code into your IDE, verify that it compiles and download to your Arduino Bonus Have the serial port send a character instead of decimal Have the LED turn on/off with each character received Have the LED turn on when N and off when F Have the Arudino print a countdown to the serial port, switching the LED state each second. Stop the countdown and start the LED blinking fast when it reaches 0. Reset countdown when R is received. If you have an analog or digital peripheral, send its value to the serial port

42 Further References Many of the examples come from: