Lab 02 Arduino 數位感測訊號處理, SPI I2C 介面實驗. More Arduino Digital Signal Process

Transcription

1 Lab 02 Arduino 數位感測訊號處理, SPI I2C 介面實驗 More Arduino Digital Signal Process

2 Blink Without Delay Sometimes you need to do two things at once. For example you might want to blink an LED (or some other timesensitive function) while reading a button press or other input. In this case, you can't use delay(), or you'd stop everything else the program while the LED blinked. The program might miss the button press if it happens during the delay(). This example demonstrates how to blink the LED without using delay(). It keeps track of the last time the Arduino turned the LED on or off. Then, each time through loop(), it checks if a long enough interval has passed. If it has, it toggles the LED on or off. 2

3 Circuit Hardware Required Arduino Board LED 3

4 Code for Blink Without Delay 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 // 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) void setup() { // set the digital pin as output: pinmode(ledpin, OUTPUT); 4

5 Code for Blink Without Delay void loop() { // here is where you'd put code that needs to be running all the time. // check to see if it's time to blink the LED; that is, if the // difference between the current time and last time you blinked // the LED is bigger than the interval at which you want to // blink the LED. unsigned long currentmillis = millis(); if(currentmillis - previousmillis > interval) { // save the last time you blinked the LED previousmillis = currentmillis; // if the LED is off turn it on and vice-versa: if (ledstate == LOW) ledstate = HIGH; else ledstate = LOW; // set the LED with the ledstate of the variable: digitalwrite(ledpin, ledstate); 5

6 millis() The code below uses the millis() function, a command that returns the number of milliseconds since the Arduino board started running its current program, to blink an LED. 6

7 Button Pushbuttons or switches connect two points in a circuit when you press them. This example turns on the built-in LED on pin 13 when you press the button. 7

8 Circuit Hardware Arduino Board momentary button or switch 10K ohm resistor breadboard hook-up wire 8

9 Schematic When the pushbutton is open (unpressed) there is no connection between the two legs of the pushbutton, so the pin is connected to ground (through the pull-down resistor) and we read a LOW. When the button is closed (pressed), it makes a connection between its two legs, connecting the pin to 5 volts, so that we read a HIGH. 9

10 Code for Button const int buttonpin = 2; const int ledpin = 13; // variables will change: int buttonstate = 0; void setup() { pinmode(ledpin, OUTPUT); pinmode(buttonpin, INPUT); // the number of the pushbutton pin // the number of the LED pin void loop(){ buttonstate = digitalread(buttonpin); if (buttonstate == HIGH) digitalwrite(ledpin, HIGH); else digitalwrite(ledpin, LOW); // variable for reading the pushbutton status // initialize the LED pin as an output: // initialize the pushbutton pin as an input: // read the state of the pushbutton value: // check if the pushbutton is pressed. // if it is, the buttonstate is HIGH: turn LED on: // turn LED off 10

11 Button State Change Detection (Edge Detection) Once you've got a pushbutton working, you often want to do some action based on how many times the button is pushed. To do this, you need to know when the button changes state from off to on, and count how many times this change of state happens. This is called state change detection or edge detection. 11

12 Schematic The sketch is same as pervious button example. It then compares the button's state to its state the last time through the main loop. If the current button state is different from the last button state and the current button state is high, then the button changed from off to on. The sketch then increments a button push counter. The sketch also checks the button push counter's value, and if it's an even multiple of four, it turns the LED on pin 13 ON. Otherwise, it turns it off. 12

13 Code for Button State Change Detection const int buttonpin = 2; const int ledpin = 13; // the pin that the pushbutton is attached to // the pin that the LED is attached to // Variables will change: int buttonpushcounter = 0; // counter for the number of button presses int buttonstate = 0; // current state of the button int lastbuttonstate = 0; // previous state of the button void setup() { // initialize the button pin as a input: pinmode(buttonpin, INPUT); // initialize the LED as an output: pinmode(ledpin, OUTPUT); // initialize serial communication: Serial.begin(9600); 13

14 Code for Button State Change Detection void loop() { buttonstate = digitalread(buttonpin); // read the pushbutton input pin: if (buttonstate!= lastbuttonstate) {// compare the buttonstate to its previous state if (buttonstate == HIGH) { // if the state has changed, increment the counter // if the current state is HIGH then the button wend from off to on: buttonpushcounter++; Serial.println("on"); Serial.print("number of button pushes: "); Serial.println(buttonPushCounter, DEC); else { // if the current state is LOW then the button wend from on to off: Serial.println("off"); 14

15 Code for Button State Change Detection // save the current state as the last state, //for next time through the loop lastbuttonstate = buttonstate; // turns on the LED every four button pushes by // checking the modulo of the button push counter. // the modulo function gives you the remainder of // the division of two numbers: if (buttonpushcounter % 4 == 0) { digitalwrite(ledpin, HIGH); else { digitalwrite(ledpin, LOW); 15

16 Interrupts in Arduino Interrupts can help solve timing issues which may occur within your code/hardware setup. You may have had timing issues already and just not understood what happened. On the Duemilanove, there are 2 hardware interrupts available. These are located on Digital Pins 2 and 3. 16

17 Circuit As same as the Button State Change Detection example 17

18 Standard Digital Input and Output - No Interrupts int pbin = 2; // Digital input on pin 2 int ledout = 13; // The output LED pin int state = LOW; // The input state void setup() { // Set up the digital Pin 2 to an Input and Pin 4 to an Output pinmode(pbin, INPUT); pinmode(ledout, OUTPUT); void loop() { state = digitalread(pbin); //Read the button digitalwrite(ledout, state); //write the LED state //Simulate a long running process or complex task for (int i = 0; i < 100; i++) { // do nothing but waste some time delay(30); 18

19 Making Use of Interrupts int pbin = 0; // Interrupt 0 is on DIGITAL PIN 2! int ledout = 13; // The output LED pin volatile int state = LOW; // The input state toggle void setup() { // Set up the digital pin 2 to an Interrupt and Pin 13 to an Output pinmode(ledout, OUTPUT); //Attach the interrupt to the input pin //and monitor for ANY Change attachinterrupt(pbin, statechange, CHANGE); void loop() { //Simulate a long running process or complex task for (int i = 0; i < 100; i++) { // do nothing but waste some time delay(30); void statechange() { state =!state; digitalwrite(ledout, state); 19

20 Attach Interrupt The attachinterrupt(param1, param2, param3) requires 3 parameters, these are; param1 = Which interrupt to listen for. This is the Interrupt Number not the Digital In number param2 = Which code function to call, this must be a method that takes no parameters and returns no value. param3 = Which condition to watch for. The Arduino can listen for 4 types of condition changes. These are; LOW = The input is at a LOW state RISING = The input state changes from LOW to HIGH FALLING = the input state changes from HIGH to LOW CHANGE = The input state changed from HIGH to LOW or LOW to HIGH, i.e. has changed its state 20

21 More Interrupts ReAssigning Interrupts Interrupts can be changed at any point by using the attachinterrupt() method. As soon as this is done, any previously assigned interrupt on the associated pin is removed. Starting / Stopping Interrupts The Arduino also has the ability to temporarily ignore all the interrupts. You may want to do this if you have some sensitive code that must be executed without interruption. In this case you would issue a nointerrupts() call. Once your sensitive code block has completed, interrupts can be restarted by calling interrupts(). Removing Interrupts Interrupts can also be removed by using the detachinterrupt(interrupt_number) method. 21

22 4 States of Traffic Light Schematic 22

23 4 States of Traffic Light Example int pinredled = 2; int pinyelled = 3; int pingrnled = 4; int lightstate = 0; void setup() { pinmode(pinredled, OUTPUT); /* Set the LED pins to output */ pinmode(pinyelled, OUTPUT); pinmode(pingrnled, OUTPUT); digitalwrite(pinredled, HIGH); /* Turn the RED light on void loop() { lightstate++; if (lightstate > 3) { // If the light state > 3, reset it to 0 (red). lightstate = 0; delay(2500); 23

24 4 States of Traffic Light Example /* Display correct light sequence */ if (lightstate == 0) { // Red digitalwrite(pinredled, HIGH); lightoff(pinyelled); lightoff(pingrnled); if (lightstate == 1) { // Red and Amber digitalwrite(pinredled, HIGH); digitalwrite(pinyelled, HIGH); lightoff(pingrnled); if (lightstate == 2) { // Green digitalwrite(pingrnled, HIGH); lightoff(pinyelled); lightoff(pinredled); 24

25 4 States of Traffic Light Example if (lightstate == 3) { // Amber-only digitalwrite(pinyelled, HIGH); lightoff(pinredled); lightoff(pingrnled); void lightoff(int pin) { digitalwrite(pin, LOW); 25

26 Classic Exercise one: Traffic light Combine the pushbutton example and the 4 states of traffic light example. Now the system add a digital switch and two new LEDs (for the crossing indicators). Initialise the lights (blink red LED 5 times, then turn on all three traffic lights) Show amber traffic light Show green traffic light and wait on green When the crossing button is pressed: (the hardware interrupt is necessary) Show the amber traffic light Show the red traffic light Show the green man Wait a preset amount of time to let the pedestrians cross Blink the green man light a few times Blink the amber traffic light a few times Extinguish the green man light and turn on the red man light Resume green traffic light Repeat! 26

27 Classic Exercise one: Traffic light The example video er_embedded 27