Transcript Week 11 - Microcontrollers

Lecture 9:
Microcontrollers – part 1
BJ Furman
29OCT2012
The Plan for Today

Microcontrollers for engineering
applications





What is a microcontroller?
How are microcontrollers used?
The Arduino hardware platform
The Spartronics Experimenter board
Programming the Arduino
Basic steps
 Digital I/O
 Analog I/O

Learning Objectives

Explain what a microcontroller is

Explain where microcontrollers are used

Describe the Arduino prototyping platform

Describe the Spartronics Experimenter board

Explain what is meant by a pin being an input
or an output

Write programs for the Arduino that can do:

Digital I/O

Analog I/O
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-todigital converters, serial communication
hardware, etc.
ATmega328
the ‘brain’ of the Arduino
http://www.amazon.com/AVR-Pin-20MHz32K-ATMega328/dp/B004G5AVS6
Where are Microcontrollers Used?

Everywhere!

Car
 Phone
 Toothbrush
 Microwave oven
 Copier
 Television
 PC keyboard
 Appliances
http://ecomodder.com/wiki/index.php/MPGuino

The Arduino Platform


Atmel ATmega328
microcontroller
14 digital I/O pins





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
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

Rx + Tx
LEDs
Pin 13 LED
Digital Pins
Power
LED
USB
jack
Reset
Button
FTDI
USB chip
Voltage
regulator
Microcontroller
power
jack
$13 ‘breadboardable’
http://arduino.cc/
Pwr/GND Pins
Analog Pins
ICSP
Header
The Spartronics Experimenter Board
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


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Momentary SPST
push-button switches
Red LEDs
Piezo speaker
Potentiometer (pot)
Temperature sensor
Light sensor
Dual 7-segment display
RGB LED
Dual 7-segment display
RGB LED
speaker
Light sensor
Pot
R
G
Cathode
B
http://www.sparkfun.com/commerce/images/products/00105-03-L_i_ma.jpg
Handling the Arduino - How NOT to Do It!
Improper Handling - NEVER!!!
Handling the Arduino - The Proper Way
Proper Handling - by the edges!!!
Programming the Arduino

An arduino program == ‘sketch’
 Must have:



setup()


setup()
loop()
configures pin modes and
registers
loop()

runs the main body of the
program forever



// 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
like while(1) {…}
Where is main() ?

/* 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 13
const int DELAY_ON = 1000;
const int DELAY_OFF = 1000;
Arduino simplifies things
Does things for you
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()

const byte ledPin = 13; // LED on digital pin 13
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 taken in
pinMode()



the world outside the
microcontroller determines
the voltage applied to the
pin


Information is sent out
Input

void setup()
{
// initialize the digital pin as an output:
pinMode(ledPin, OUTPUT);
}

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 …  ?
where can you find out about
the commands, etc?
http://arduino.cc/en/Reference/Extended
Blinking the LED in loop()

digitalWrite()



#define LED_PIN 13 // LED on digital pin 13
#define DELAY_ON 500 // in ms
#define DELAY_OFF 100
Causes the voltage on the
indicated pin to go HIGH
(+5V) or LOW (0V)
Note: must first configure the
pin to be an output
void setup()
{
// initialize the digital pin as an output:
pinMode(LED_PIN, OUTPUT);
}
 To make pin go to 5V (high):
void loop()
 digitalWrite(pin_num,HIGH);
{
 Best to #define pin num. digitalWrite(LED_PIN, HIGH); // turn LED on
delay(DELAY_ON); // wait for DELAY_ON ms
 To make pin go to 0V (low):
digitalWrite(LED_PIN, LOW); // turn LED off
 digitalWrite(pin_num,LOW);
delay(DELAY_OFF); // wait for DELAY_OFF ms
}
delay()

Causes the program to wait for
a specified time in milliseconds
http://arduino.cc/en/Reference/Extended
Spartronics Experimenter Button Pinout
To ATmega328

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’

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
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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
12
8
7
4
Pull-up Resistor Concept
Pull-up resistor OFF
Pull-up resistor ON
ATmega328
ATmega328
Pull-up resistor
VTG= +5V
1
PD3
0
VTG= +5V
1
PD3
0
Spartronics Experimenter LED Pinout

Pin and LED map





11 - LED0 (red)
9 - LED1 (red) or RGB (green)
6 - LED2 (red) or RGB (blue)
3 - LED3 (red) or RGB (red)
13 - LED on Arduino
Jumper determines whether pins
map to red LEDs or the RGB
11
9
6
3
Spartronics Experimenter Digital Pin
Assignments
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
LED0
pwm
pwm
pwm
pwm
LED1
LED2
LED3
green
blue
red
piezo
servo
SW0
SW1
SW2
SW3
Spartronics Experimenter Analog Pin
Assignments
7
6
5
4
3
2
1
0
photocell
POT
temp sensor
Code to Set Up Button Pins

Two steps:
1.
Make the pin an
INPUT

2.
pinMode()
Turn the pull-up
resistor on

const byte SW0 =
const byte SW1 =
const byte SW2 =
const byte SW3 =
12;
8;
7;
4;
// button SW0
// button SW1
// button SW2
// button SW3
void setup()
{
pinMode(SW0, INPUT); // make SW0 an INPUT
digitalWrite(SW0, HIGH); // turn on pullup resistor
etc.
}
digitalWrite()
a 1 to the pin
(See full_test.pde for a more elegant approach to setting up button pins)
Digital I/O Example - Problem Statement

Write a program to turn on the blue of the
RGB LED (connected to digital pin 6)
when SW0 is pressed (off otherwise)

Pseudocode:
define pin assignments
 configure pins (which are input, which are output)
 loop forever

if SW0 button is pressed
 make pin 6 high
 else
 make pin 6 low

Digital I/O Example - Pin Assignment and
Configuration

Refine the pseudocode:

define pin assignments



const byte RGB_blue_pin = 6;
const byte SW0_pin = 12;
configure pins (in function setup())

RGB_blue_pin


SW0_pin


make it an OUTPUT
_______
INPUT
make it an ______
turn on pull-up resistor on
SW0 pin


pin will read high (1) until
pulled low (0)
see schematic
void setup()
{
pinMode(RGB_blue_pin, OUTPUT);
pinMode(SW0_pin, INPUT);
digitalWrite(SW0_pin, HIGH);
}
Digital I/O Example - loop() Algorithm

Refine the pseudocode, cont.:

loop forever (use function loop())

If button is not pressed:



high (5V)
voltage on button pin 12 will be _______
make pin 6 voltage low (LED will go off or stay off)
If button is pressed:


low (0V)
voltage on button pin 12 will be _______
make pin 6 voltage high (LED will go on or stay on)
void loop()
{
if(digitalRead(SW0_pin) == LOW)
{
digitalWrite(RGB_blue_pin, HIGH);
}
else
{
digitalWrite(RGB_blue_pin, LOW);
}
}
Digital I/O Example - Arduino Program


Arduino program
Suppose a change to the
specifications:


LED is on until button
pressed, then off
Contrast mechatronic
approach vs. nonmechatronic



re-wire, or…
re-program
the mechatronics
approach separates
the sensing elements
from the control
elements
/* 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);
digitalWrite(SW0_pin, HIGH);
}
/* loop forever */
void loop()
{
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, HIGH);
else
digitalWrite(RGB_blue_pin, LOW);
}
Digital I/O Example - Modification

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
/* 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);
digitalWrite(SW0_pin, HIGH);
}
/* loop forever */
void loop()
{
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, HIGH);
else
digitalWrite(RGB_blue_pin, LOW);
}
Comparison of Digital I/O Programs
/* Blue_LED_button_cntrl1 - turns on blue LED
when SW0 on Experimenter board is pressed, off
otherwise */
/* Blue_LED_button_cntrl2 - turns off blue LED
when SW0 on Experimenter board is pressed, on
otherwise */
/* pin assignments */
const byte RGB_blue_pin = 6;
const byte SW0_pin = 12;
/* 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);
digitalWrite(SW0_pin, HIGH);
}
/* configure pins */
void setup()
{
pinMode(RGB_blue_pin, OUTPUT);
pinMode(SW0_pin, INPUT);
digitalWrite(SW0_pin, HIGH);
digitalWrite(RGB_blue_pin, HIGH);
}
/* loop forever */
void loop()
{
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, HIGH);
else
digitalWrite(RGB_blue_pin, LOW);
}
/* loop forever */
void loop()
{
if(digitalRead(SW0_pin) == LOW)
digitalWrite(RGB_blue_pin, LOW);
else
digitalWrite(RGB_blue_pin, HIGH);
}
Analog In with
Serial Out
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Read the POT

Note: analog voltage!
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0V0
5 V  1023
Blink an LED at a
rate proportional to
the pot voltage
Output the pot
voltage to the serial
monitor



Initialize with
Serial.begin()
Map voltage to delay
Write a line with
Serial.print or
Serial.println
#define MAX_DELAY_TIME 1000 // max delay in ms
#define MIN_DELAY_TIME 10 // min delay in ms
#define MAX_POT_VALUE 855 // max pot reading
#define MIN_POT_VALUE 0 // min pot reading
const byte potPin = 1; // pot output on pin 1
const byte ledPin = 6; // blue LED on pin 6
unsigned int potVoltage = 0; // value of pot voltage
unsigned int delay_ms;
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(potPin, INPUT);
Serial.begin(9600); // init serial comm at 9600 bps
}
void loop() {
potVoltage = analogRead(potPin); // read pot
delay_ms =
map(potVoltage,MIN_POT_VALUE,MAX_POT_VALUE,MIN
_DELAY_TIME,MAX_DELAY_TIME);
Serial.print("sensor = " ); // print to monitor
Serial.print(potVoltage);
Serial.print(" delay, ms = " );
Serial.println(delay_ms); // print delay and linefeed
digitalWrite(ledPin, HIGH); // turn the LED on
delay(delay_ms); // wait for delay_ms
digitalWrite(ledPin, LOW); // turn the LED off:
delay(delay_ms); // wait for delay_ms
}
POT_input_Serial_Out.pde
Effect of Using delay()
Leads to poor (slow) performance as delay
time increases
 Try to avoid long delays




Use millis() instead
Check for time exceeding millis() + delay_time
Ex. POT_in_Serial_Out.pde


Note also the use of #ifdef for ‘conditional compilation’
Note how roll-over of millis() is handled
Analog Out (PWM) Concept

No facility exists on most microcontrollers
to directly output an analog voltage (i.e., a
voltage that varies continuously over the
range of 0 to 5V) 5V
time

Use Pulse Width Modulation (PWM) to
approximate an analog voltage
Digital outputs are capable of 0V or 5V
 Over a fraction (ton) of a time period tcycle, keep pin
at 5V, the rest of the time, at 0V

The average voltage is proportional to ton/tcycle, which is
called the ‘Duty Cycle’
 See Lab View PWM_demo.vi

Front Panel
30% duty
cycle
Block Diagram
Arduino analogWrite( )

analogWrite(pin, value);

0  value  255
0% duty cycle --> 0 V --> analogWrite(pin, 0);
 100% duty cycle --> 5 V --> analogWrite(pin, 255);


fade_example.pde (see next page)
Analog Output Example

Fade the red
LED in, then
out


duty cycle is
incremented
then
decremented
256 steps

0% to 100%
const byte ledPin = 3; // red RGB LED on Experimenter
const byte FADE_MAX = 255; // max value for setting duty cycle
const byte FADE_INC = 5; // increment for changing duty cycle
void setup()
{
pinMode(ledPin, OUTPUT);
}
void loop()
{
int fadeValue; // PWM value
// fade in from min to max in increments of 5 points:
for(fadeValue = 0 ; fadeValue <= FADE_MAX; fadeValue +=FADE_INC)
{
analogWrite(ledPin, fadeValue); // sets the value (range from 0 to 255):
}
// fade out from max to min in increments of 5 points:
for(fadeValue = FADE_MAX; fadeValue >= 0; fadeValue -=FADE_INC)
{
analogWrite(ledPin, fadeValue); // sets the value (range from 0 to 255):
}
}
fade_example.pde
Review
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/

Spartronics Experimenter Board