A short presentation of Arduino microcontroller

IntroductionATmega328p µC

Language Reference

Micro-controller programming: a case of study

Part I

Daniele Carnevale

June 23, 2010

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List of ContentsArduino Microcontroller boardArduino programming overview

List of Contents - Part I

Contents

The Arduino microcontroller board

ATmel AVR-8bit Microcontroller (µC)

Memory, ADC, DAC, Timers...

Programming the µC via Arduino IDE

Language programming

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Arduino Microcontroller board

FTDI FT232RL USB-to-TTLa (5V) Serialchip (FTDI drivers provide a virtual com port)

aTransistor-Transistor Logic.bUniversal asynchronous receiver/transmitter.cIn-Circuit Serial Programming

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Capacitors, Jack, Voltage regulators,6-20V (recommended 7-12V) → 5V...

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Digital pins, Gnd, Aref, UARTb TTL (5V

serial communication on pins 0-RX and 1-TX)

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Analog pins and power

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External clock (16MHz), reset, ICSPc

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ATmel328p microcontroller

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ATmel328p microcontroller

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Arduino Microcontroller board (cont’d)

From the www.arduino.cc home page:

“Arduino is an open-source electronics prototyping platformbased on flexible, easy-to-use hardware and software. It’sintended for artists, designers, hobbyists, and anyoneinterested in creating interactive objects or environments.”

born to make a device for controlling student-built interactiondesign projects (Bar of Design Institute of Ivrea by MassimoBanzi and collaborators - 2005 )

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Arduino Microcontroller board (cont’d)

Sensors, actuators,electronic hardware

Continuous anddigital signals

⇐⇒

Arduino Board

Signal wiring andconditioning

ATmel328p µC

Signal processing andcomputation

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Arduino programming

Arduino programming language

Based on open-source Wiring language: a simplified C++“customized” to easily interface with electronics (I/O).

AVR Libc package that provides a subset of the standard Clibrary for Atmel AVR 8-bit RISC microcontrollers

Avr-GCC compiler

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Arduino programming

Arduino programming language

Based on open-source Wiring language: a simplified C++“customized” to easily interface with electronics (I/O).

AVR Libc package that provides a subset of the standard Clibrary for Atmel AVR 8-bit RISC microcontrollers

Avr-GCC compiler

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Arduino programming

int ledPin = 0; // LED connected to digital pin 0

void setup()

pinMode(ledPin, OUTPUT); // set ledPin pin as output

void loop()

digitalWrite(ledPin, HIGH); // set the LED on

delay(1000); // wait for a second

digitalWrite(ledPin, LOW); // set the LED off

delay(1000); // wait for a second

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Arduino programming (cont’d)

Arduino programming IDE

Created with Processing contains a code editor with messagearea, text console and a toolbar to interface with Arduino hardwareand to upload code

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Arduino programming IDE

Created with Processing contains a code editor with messagearea, text console and a toolbar to interface with Arduino hardwareand to upload code

Processing

Processing is an open-source programming language oriented forvisual applications, animation and interaction:

The Processing Development Environment (PDE)

A collection of functions (commands or methods)

A Java-like language syntax

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The Arduino IDE allows to:

Create anew/Open/close sketch(source file)

Verify and compile thecode

Upload the code to theonboard-µC’s Flashmemory

Open/Stop the serialmonitor tocommunicate with theµC

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Overviewbootloader

ATmega328p: overview

ATmel picoPower Microcontroller ATmega328p :

AVR1-8 bit RISC2 technology, 0-20MHz@1.8V - 5.5V

1The AVR is a modified Harvard architecture 8-bit RISC single chipmicrocontroller developed by Atmel in 1996

2Reduced Instruction Set Computer3Electrically Erasable Programmable Read-Only Memory, it is non-volatile.4Million Instructions Per Second.

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Overviewbootloader

32KB self-programming Flash Program Memory, 2KB SRAM,1KB EEPROM3

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Overviewbootloader

8 Channel 10-bit A/D-converter, 14 Digital I/O Pins (ofwhich 6 provide PWM output)

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Overviewbootloader

debugWIRE On-chip Debug System

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Overviewbootloader

Up to 20 MIPS4 throughput at 20 MHz

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Overviewbootloader

Up to 20 MIPS4 throughput at 20 MHz

(on Arduino board) 1/16MHz = 62.5ns per CPU (clock) cycle1The AVR is a modified Harvard architecture 8-bit RISC single chip

microcontroller developed by Atmel in 19962Reduced Instruction Set Computer3Electrically Erasable Programmable Read-Only Memory, it is non-volatile.4Million Instructions Per Second.

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Overviewbootloader

Schematic of ATmega328p

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Overviewbootloader

ATmega328p: some features...

Two 8-bit Timer/Counters with Separate Prescaler and CompareMode

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Overviewbootloader

One 16-bit Timer/Counter with Separate Prescaler, Compare Mode,and Capture Mode

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Overviewbootloader

Real Time Counter with Separate Oscillator

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Overviewbootloader

6 PWM Channels

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Overviewbootloader

6 PWM Channels, usually 500 Hz but it can be changed:

//The code to set the PWM frequency

// Set pin 9’s PWM frequency to 3906 Hz (31250/8 = 3906)

// Note that the base frequency for pins 3, 9, 10, and 11 is

// 31250 Hz

setPwmFrequency(9, 8);

// Note that the base frequency for pins 5 and 6 is 62500 Hz

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Overviewbootloader

6 PWM Channels (8 bit-DAC)

6-channel 10-bit ADC (successive approximation). The samplingrequires 12− 260µs (83-3.8KHz).Quantization: [0, 5V ] → [0, 1023] =⇒ 4.9mV per level. In somecase the quantization can be improved attaching the voltage Vref atthe AREF pin and calling analogReference(EXTERNAL), which setsthe voltage range for sampling as [0, Vref ] → [0, 1023].

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Overviewbootloader

6-channel 10-bit ADC

Programmable Serial USART - 2Mb (Universal Syncronous -Asynchronous Receiver - Transmitter) on digital pins 0(RX) and1(TX)

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Overviewbootloader

Programmable Serial USART - 2Mb

Master/Slave SPI - 8Mb/4Mb (Serial Peripheral Interface) on pins10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK).

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Overviewbootloader

Master/Slave SPI - 8Mb/4Mb

Byte-oriented 2-wire Serial Interface ( < 1Mb) , Philips I2C(Integrate to Circuit) compatible on digital pins 4 (SDA) and 5(SCL) using the Wire library.

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Overviewbootloader

Byte-oriented 2-wire Serial Interface ( < 1Mb)

Programmable Watchdog Timer with Separate On-chip Oscillatorat 128KHz (see pag. 50 and avr/wdt.h). Used as an internalinterrupt.

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Overviewbootloader

Byte-oriented 2-wire Serial Interface ( < 1Mb)

Programmable Watchdog Timer

External interrupts and Wake-up on digital pin 2 and 3 change.

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Overviewbootloader

The Arduino bootloaderWhen powered-on, the Bootloader runs first determining whetherto re-program or jump to the main application (the newestuploaded sketch). When uploading the new code via Arduinosoftware:

The µC is resetThe pre-loaded Arduino bootloader (2KB of the Flashmemory) runs (Arduino’s buit-in LED blinks)The bootloader starts the initial configuration. If new code isarriving from the serial port it is saved into the Flash memoryThe bootloader runs the newest uploaded sketch

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Overviewbootloader

The Arduino bootloaderWhen powered-on, the Bootloader runs first determining whetherto re-program or jump to the main application (the newestuploaded sketch). When uploading the new code via Arduinosoftware:

The µC is resetThe pre-loaded Arduino bootloader (2KB of the Flashmemory) runs (Arduino’s buit-in LED blinks)The bootloader starts the initial configuration. If new code isarriving from the serial port it is saved into the Flash memoryThe bootloader runs the newest uploaded sketch

Burning the bootloader

Via an AVR-ISP (in-system programmer), USBtinyISP or aParallelProgrammer connected the ICSP pins and the softwareprovided by Arduino IDE.Arduino itself can be programmed as an ISP. 43 / 70

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The main structuresFunctionsMemorySerial communicationInterrupts

The main structures

When the bootloader runs thesketch:

setup() function is executedonce

the loop() function isexecuted repeatedly until theµC is powered-off, a reset istriggered, or an interrupt(internal or external) forcesthe ISRa execution: the µCjumps back to execute theloop() code once the ISR isperformed.

aInterrupt service routine.

Bootloader Power on

Initialization: pin settings,

serial communication,

interrupt service routine...

Setup()

Loop()

’Endless’ executed code...ISR

Interrupt

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Example: setup() and loop() functions

int buttonPin = 3;

void setup()

Serial.begin(9600);

pinMode(buttonPin, INPUT);

// loop checks the button pin each time,

// and will send serial if it is pressed

void loop()

if (digitalRead(buttonPin) == HIGH)

serialWrite(’H’);

serialWrite(’L’);

delay(1000);

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Control Structures

almost like C...

if...else

switch case

do... while

continue

return

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Operators

almost like C...

Aritmetic =,∗, %...

Comparison ==,! = ...

Boolean &&, ||, !

Pointer ⋆, &

Bitwise &, |, <<...

Compound ++, / =, & =, | =...

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Variables

almost like C...

Constants HIGH — LOW, INPUT — OUTPUT, true — false,integer and floating point constants

Data types void, boolean, char, unsigned char, byte, int, word,long, double, array, string . . .

Conversion char(), byte(), int(), float() . . .

Qualifiers variable scope, static, volatile, const

Utilities sizeof()

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Functions (AVR Libc)

Digital I/O

pinMode(pin,mode)void setup(){ pinMode(ledPin, OUTPUT); // sets the digital pin as}

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Digital I/O

pinMode(pin,mode)

digitalWrite(pin, value) [< 4µs → 64 CPU Clocka]digitalWrite(ledPin, HIGH); // sets the LED on

aCPU clock is 1/16MHz= 62.5ns.

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Digital I/O

pinMode(pin,mode)

digitalWrite(pin, value) [< 4µs → 64 CPU Clock]

int digitalRead(pin) [< 4µs → 64 CPU Clock]

#define inPin 7 // pushbutton connected to digital pin 7int val = 0; // variable to store the read value

void setup() {pinMode(ledPin, OUTPUT); // sets the digital pin 13 as outputpinMode(inPin, INPUT); // sets the digital pin 7 as input }

void loop(){val = digitalRead(inPin); // read the input pin

digitalWrite(ledPin, val); //sets the LED to the button’s value }

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Functions (cont’d)

Analog I/O

analogReference(type) , where type is

DEFAULT : 5VINTERNAL: 1.1V (≥ATmega328p), 2.5V (ATmega8)EXTERNAL: external voltage applied at pin AREF (Vref )

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Analog I/O

int analogRead(pin) [< 260µs → 4160 CPU Clock]

#define inPin 7 // pushbutton connected to digital pin 7int val = 0; // variable to store the read value

void setup(){Serial.begin(9600); // setup serial}

void loop(){val = analogRead(inPin); // read the input pin

digitalWrite(ledPin, val); // sets the LED to the button’s value}

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Analog I/O

int analogRead(pin) [< 260µs → 4160 CPU Clock]

analogWrite(pin, value) (PWM - value

255% Duty Cycle) )

[< 12µs → 192 CPU Clock]

int ledPin = 9; // LED connected to digital pin 9int analogPin = 3; // potentiometer at analog pin 3

void setup() {// sets the ledPin as a PWM output (not necessary)pinMode(ledPin, OUTPUT); }

void loop(){analogWrite(ledPin, analogRead(analogPin)/4);

// analogRead values ∈ [0,1023], analogWrite values ∈ [0, 255]}

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unsigned long millis() [< 4µs → 64 CPU Clock]

unsigned long micros() [< 4µs → 64 CPU Clock]

delay(ms)

delayMicroseconds(us)

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Math, Bits and Bytes

min(x,y), max(x,y), abs(x), constraint(x,a,b)...

sin(rad), cos(rad), tan(rad)

randomSeed(seed), random(max), random(min,max)

lowByte(x), highByte(x),bitRead(x,n). . .

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Memory manipulation

Flash memory [32KB, 10K read/write]

Specific type of EEPROM storing the bootloader(2KB) and sketch. Use

the PROGMEM instruction to manipulate it.

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Memory manipulation

SRAM [2KB]

Is where all the sketch variables are placed.

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Memory manipulation

SRAM [2KB]

Is where all the sketch variables are placed.

EEPROM [1KB, 100K read/writes]

Can be used like a µHard Disk using the EEPROM library. Note: each

read/write operation requires about 3.5ms.

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Serial communication via RS232

Serial functions

Serial.

begin(bauda), baud= [300, 1200, 2400, 4800, 9600, . . . , 115200]

available()

read()

flush()

print(val, format)

println(val, format)

write()

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Serial communication: example

int inByte = 0; // for incoming serial data

void setup()

Serial.begin(9600);

void loop()

// read from port 0

if (Serial.available())

inByte = Serial.read();

Serial.print(inByte, BYTE);

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Serial communication

Depending on the serial port settings (start bit, parity bit...),usually 10 bits are sent over the port to transmit a byte→ 9600/10 = 960 bytes per second.

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to send 2 bytes of data (e.g. a value measured from ADC)⇒ 960/2 = 480 samples per second (sps)

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to send 2 bytes of data (e.g. a value measured from ADC)⇒ 960/2 = 480 samples per second (sps)

The function Serial.print(val, format) takes its own time...at19200 baud to send 2 bytes data it should require 1/960s,measured 2.5− 3ms. . .

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Interrupts

Re-enabling and disabling interrupts

noInterrupts() disables interrupts

interrupts() re-enable interrupts (normally enabled atpowered-on)

Example:

void setup() {}

void loop(){ noInterrupts();// critical, time-sensitive code hereinterrupts();

// other code here

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External Interrupts

attachInterrupt(interrupt, function, mode)

interrupt: 0 (on digital pin 2) and 1 (on digital pin 3)

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External Interrupts

function: interrupt service routine (ISR) that must take noparameters and return nothing. Usually it modifies volatilevariables.

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External Interrupts

LOW to trigger the interrupt whenever the pin is low,CHANGE whenever the pin changes valueRISING when the pin goes from low to high,FALLING when the pin goes from high to low.

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External Interrupts

LOW to trigger the interrupt whenever the pin is low,CHANGE whenever the pin changes valueRISING when the pin goes from low to high,FALLING when the pin goes from high to low.

detachInterrupt(interrupt)....

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attachInterrupt(interrupt, function, mode): example

//A digital signal is attached to the pin 2 (interrupt 0),

//but you do not measure it directly...

int pin = 13;

volatile int state = LOW;

void setup()

pinMode(pin, OUTPUT);

attachInterrupt(0, blink, CHANGE);

void loop()

digitalWrite(pin, state);

void blink() //ISR associated to the interrupt 0 (digital pin 2)

state = !state;

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A short presentation of Arduino microcontroller

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