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Lecture 9: Microcontrollers – part 1

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

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Lecture 9: Microcontrollers – part 1

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  1. Lecture 9: Microcontrollers – part 1 BJ Furman 29OCT2012

  2. 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

  3. 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

  4. 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. ATmega328the ‘brain’ of the Arduino http://www.amazon.com/AVR-Pin-20MHz-32K-ATMega328/dp/B004G5AVS6

  5. Where are Microcontrollers Used? • Everywhere! • Car • Phone • Toothbrush • Microwave oven • Copier • Television • PC keyboard • Appliances • http://ecomodder.com/wiki/index.php/MPGuino

  6. The Arduino Platform Digital Pins Pin 13 LED Rx + TxLEDs • 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 • $22 - $30 built • $13 ‘breadboardable’ PowerLED ResetButton USBjack FTDIUSB chip Voltageregulator ICSPHeader Microcontroller powerjack Analog Pins Pwr/GND Pins http://arduino.cc/

  7. R B G Cathode The Spartronics Experimenter Board • Momentary SPSTpush-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 http://www.sparkfun.com/commerce/images/products/00105-03-L_i_ma.jpg

  8. Handling the Arduino - How NOT to Do It! Improper Handling - NEVER!!!

  9. Handling the Arduino - The Proper Way Proper Handling - by the edges!!!

  10. Programming the Arduino /* 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; // 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 } • 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

  11. Using setup() const byte ledPin = 13; // LED on digital pin 13 void setup() { // initialize the digital pin as an output: pinMode(ledPin, OUTPUT); } • 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 • pinMode() • sets whether a pin is an inputor 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 aboutthe commands, etc? http://arduino.cc/en/Reference/Extended

  12. 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

  13. 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’ • 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

  14. Pull-up Resistor Concept Pull-up resistor OFF Pull-up resistor ON ATmega328 ATmega328 VTG= +5V VTG= +5V Pull-up resistor 1 1 PD3 PD3 0 0

  15. 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

  16. Spartronics Experimenter Digital Pin Assignments

  17. Spartronics Experimenter Analog Pin Assignments

  18. Code to Set Up Button Pins • Two steps: • Make the pin an INPUT • pinMode() • Turn the pull-up resistor on • digitalWrite() a 1 to the pin const byte SW0 = 12; // button SW0 const byte SW1 = 8; // button SW1 const byte SW2 = 7; // button SW2 const byte SW3 = 4; // button SW3 void setup() { pinMode(SW0, INPUT); // make SW0 an INPUT digitalWrite(SW0, HIGH); // turn on pullup resistor etc. } (See full_test.pde for a more elegant approach to setting up button pins)

  19. 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

  20. 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 • make it an _______ • SW0_pin • make it an ______ • turn on pull-up resistor on SW0 pin • pin will read high (1) until pulled low (0) • see schematic OUTPUT INPUT void setup() { pinMode(RGB_blue_pin, OUTPUT); pinMode(SW0_pin, INPUT); digitalWrite(SW0_pin, HIGH); }

  21. Digital I/O Example - loop() Algorithm • Refine the pseudocode, cont.: • loop forever (use function loop()) • If button is not pressed: • voltage on button pin 12 will be _______ • make pin 6 voltage low (LED will go off or stay off) • If button is pressed: • voltage on button pin 12 will be _______ • make pin 6 voltage high (LED will go on or stay on) high (5V) low (0V) void loop() { if(digitalRead(SW0_pin) == LOW) { digitalWrite(RGB_blue_pin, HIGH); } else { digitalWrite(RGB_blue_pin, LOW); } }

  22. Digital I/O Example - Arduino Program /* 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); } • Arduino program • Suppose a change to the specifications: • LED is on until button pressed, then off • Contrast mechatronic approach vs. non-mechatronic • re-wire, or… • re-program • the mechatronics approach separates the sensing elements from the control elements

  23. Digital I/O Example - Modification /* 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); } • 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

  24. Comparison of Digital I/O Programs /* 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; /* 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, LOW); else digitalWrite(RGB_blue_pin, HIGH); } /* 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); }

  25. Analog In with Serial Out #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 } • Read the POT • Note: analog voltage! • 0 V 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 POT_input_Serial_Out.pde

  26. 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

  27. 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) 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 5V time

  28. Front Panel 30% duty cycle Block Diagram

  29. 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)

  30. Analog Output Example 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 the red LED in, then out • duty cycle is incremented then decremented • 256 steps • 0% to 100% fade_example.pde

  31. Review

  32. 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/

  33. Spartronics Experimenter Board

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