Lecture 7: Microcontrollers & I/O

Bryan Burlingame

14 October 2015

Smart, connected products require a rethinking of design. At the most basic level, product development shifts from largely mechanical engineering to a true interdisciplinary systems engineering.Porter, M., & Happelmann, J. (2015, October). How Smart, Connected Products Are Transforming Companies. Harvard Business Review, 96-112, 114.

Announcements Exam in two weeks

This is the final lecture which will be on the exam

Homework #3 due up front Homework #4 (exam review) posted

Due with the mid-term Read Ch. 3 -4 in text Open lab Wednesday evenings, 5:15

Eng 213 Arduino lab kits available from Eric Wertz

The Plan for Today How can I interact with the user

Obtaining input from the keyboard Brief decisions

Microcontrollers for engineering applications What is a microcontroller? How are microcontrollers used? The Arduino hardware platform The Spartronics Experimenter board Programming the Arduino

5

scanf() function (just a brief treatment!)

scanf() is like the reverse of printf It reads data entered via the keyboard Similarities to printf():

Needs a format string first Many common format specifiers, which indicate the type of

data expected from the keyboard Which must match the data arguments

Any number of data arguments Differences from printf():

Data argument identifiers must be preceded with an ampersand (&)

The & ahead of the variable signifies the address in memory where the data will be stored (its a pointer to the variable)

Beware!!! Forgetting the & is a common error. More on the & later this semester

6

scanf() function, cont. Differences from printf(), cont.:

Characters other than a conversion string, a space, a newline character, or a vertical tab must match characters in the input stream

A space, horizontal tab, or newline character in the format string causes scanf() to skip over leading white space up to the next nonspace character

scanf(“Distance= %lf", &num1); Will skip leading spaces before the value num1 Must find a match to the string literal, Distance= (or else

it will stop reading the input and will return the number of successful conversions that were stored (try entering a space before typing Distance=)

Darnell & Margolis (1996)

7

scanf example Prompt the user for two floating point numbers, and store them in

floating point variables of type double named x and y

#include <stdio.h>int main( void ){ float x = 0; float y = 0; char buffer[BUFF_SIZE]; printf( "Enter two floats (x y): "); scanf( "%f %f", &x, &y ); printf( “You entered %f and %f\n”, x, y ); return 0;}

More robust input We use two commands to properly obtain

input from the keyboard fgets & sscanf fgets places data collected form the

keyboard into a buffer stored as a character string up to a carriage return (when the user presses return or enter)

fgets( buffer, sizeof(buffer), stdin );

Formatted Input (2)

sscanf is from the *scanf family We’ll use fscanf later in the semester

sscanf splits the input into variables Uses conversion metasymbols like scanf sscanf( buffer, “%d %f”, &x, &y); Avoids many (though not all) weaknesses

in scanf Realistically, don’t use scanf… well ever

Formatted Input (3)#include <stdio.h>#define BUFF_SIZE 100 //note symbolic const

int main( void ){ float x = 0; float y = 0; char buffer[BUFF_SIZE]; printf( "Enter two floats (x y): "); fgets( buffer, sizeof(buffer), stdin ); sscanf( buffer, "%f %f", &x, &y ); printf( “You entered %f and %f\n”, x, y ); return 0;}

Flow control

These Boolean operations are used along with flow control (or branching) statements to control the flow of a program

DecisionsTrue False

Simple if - exampleint speed = 5; 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 themelse{ // note the indentation.

printf( “You are not speeding\n” );}

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.

http://www.amazon.com/AVR-Pin-20MHz-32K-ATMega328/dp/B004G5AVS6

ATmega328the ‘brain’ of the Arduino

Where are Microcontrollers Used?

Everywhere! Car (50 – 70 per car! (EDT Design News, July 2009))

Phone Toothbrush Microwave oven Copier Television PC keyboard Appliances

The Arduino Platform 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 $10 - $30 built

$13 ‘breadboardable’

FTDIUSB chip

Digital Pins

Analog Pins

USBjack

Microcontrollerpowerjack

Voltageregulator

Pwr/GND Pins

ICSPHeader

ResetButton

PowerLED

Pin 13 LEDRx + TxLEDs

http://arduino.cc/

The Spartronics Experimenter Board Momentary SPST

push-button switches Red LEDs Piezo speaker Potentiometer (pot) Temperature sensor Light sensor RGB LED

http://www.sparkfun.com/commerce/images/products/00105-03-L_i_ma.jpg

Cathode

R

GB

speaker

Pot

RGB LED

Light sensor

Handling the Arduino - How NOT to Do It!

Improper Handling - NEVER!!!

Handling the Arduino - The Proper Way

Proper Handling - by the edges!!!

Recall: Fundamental Flow of a C Program

Start

Main

EndReturn value to Operating System (very important!)

Calling parametersAvailable from Operating System

Fundamental Flow of an Arduino Program

Start

Setup

Loop

End

Programming the Arduino An arduino program == ‘sketch’

Must have: setup() loop()

setup() configures pin modes and

registers loop()

runs the main body of the program forever

like while(1) {…} Where is main() ?

Arduino simplifies things Does things for you

/* Blink - turns on an LED for DELAY_ON msec, then off for DELAY_OFF msec, and repeats*/const byte ledPin = 13; // LED on digital pin 13const int DELAY_ON = 1000;const int DELAY_OFF = 1000;

// setup() method runs once, when the sketch starts

void setup(){ // initialize the digital pin as an output: pinMode(ledPin, OUTPUT); }

// loop() method runs forever,// as long as the Arduino has power

void loop() { digitalWrite(ledPin, HIGH); // set the LED on delay(DELAY_ON); // wait for DELAY_ON msec digitalWrite(ledPin, LOW); // set the LED off delay(DELAY_OFF); // wait for DELAY_OFF msec}

Using setup() 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

const byte ledPin = 13; // LED on digital pin 13

void setup(){ // initialize the digital pin as an output: pinMode(ledPin, OUTPUT); }

where can you find out aboutthe commands, etc?

http://arduino.cc/en/Reference/Extended

pinMode() sets whether a pin is an

input 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 … ?

Blinking the LED in loop() digitalWrite()

Causes the voltage on the indicated pin to go HIGH (+5V) or LOW (0V)

Note: must first configure the pin to be an output

To make pin go to 5V (high): digitalWrite(pin_num,HIGH);

Best to #define pin num. To make pin go to 0V (low):

digitalWrite(pin_num,LOW);

delay() Causes the program to wait for

a specified time in milliseconds

#define LED_PIN 13 // LED on digital pin 13#define DELAY_ON 500 // in ms#define DELAY_OFF 100

void setup(){ // initialize the digital pin as an output: pinMode(LED_PIN, OUTPUT); }void loop() { digitalWrite(LED_PIN, HIGH); // turn LED on delay(DELAY_ON); // wait for DELAY_ON ms digitalWrite(LED_PIN, LOW); // turn LED off delay(DELAY_OFF); // wait for DELAY_OFF ms}

http://arduino.cc/en/Reference/Extended

Spartronics Experimenter LED Pinout

Pin and LED map 11 - LED0 (red) or RGB (red) 9 - LED1 (red) or RGB (green) 6 - LED2 (red) or RGB (blue) 3 - LED3 (red) 13 - LED on Arduino

Jumper determines whether pins map to red LEDs or the RGB

11 9 6 3

13 12 11 10 9 8 7 6 5 4 3 2 1 0

SCK MISO MOSI SS OC1 ICP AIN1 AIN0 T1 T0 INT1 INT0 TXD RXD

LED LED LED

Pwm pwm pwm pwm pwm pwm

LED0 LED1 LED2 LED3

Red Green Blue (v1 red)

Piezo

servo

SW0 SW1 SW2 speaker SW3

Spartronics Experimenter Digital Pin Assignments

12 8 7 4

Spartronics Experimenter Button Pinout

Pin and Button map 12 - SW0 8 - SW1 7 - SW2 4 - SW3

How should the associated pins be configured: as INPUTS or as OUTPUTS?

‘Active LOW’ Voltage on pin changes

from 5V to 0V when switch is pressed

Need to turn on internal ‘pull-up’ resistor, so that 5V is supplied to pin

To ATmega328

Pull-up Resistor Concept

ATmega328

PD3

VTG= +5V

0

1

ATmega328

PD3

VTG= +5V

0

1

Pull-up resistor OFF Pull-up resistor ON

Pull-up resistor

Simple if – example (Arduino)#define BUTTONPIN 12#define LEDPIN 3int buttonState = 0;void setup(){

pinMode( LEDPIN, OUTPUT );pinMode( BUTTONPIN, INPUT_PULLUP );

}void loop(){

int buttonState = digitalRead( BUTTONPIN );if( buttonState == LOW ) //note double == for equivalence{ //If the button is pressed, turn on the LED

digitalWrite( LEDPIN , HIGH);} else{ // otherwise, turn it off

digitalWrite( LEDPIN , LOW);}

}

References

Microcontroller. (2009, November 20). In Wikipedia, the free encyclopedia. Retrieved November 21, 2009, from http://en.wikipedia.org/wiki/Microcontroller

Arduino Home Page. (2009, November 21). Retrieved November 21, 2009, from http://arduino.cc/