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--- arduino:arduino_crash_course:digital_input [2012/11/05 18:58] – [Toggling state] mithat
+++ arduino:arduino_crash_course:digital_input [2017/12/06 01:13] (current) – [Digital Input] mithat
@@ Line 3: / Line 3: @@
 The Arduino literature refers to "digital" inputs, and while this is strictly accurate, a better name for these kinds of inputs is "Boolean" or "logical" inputs. However, we will use the more common "digital input" to avoid confusion.
-An Arduino digital input is one that responds to two different levels; anything above a certain voltage (but lower than the Arduino's supply voltage) is considered HIGH, and anything below a certain voltage (but not below 0 volts) is considered LOW. Anything in between is not defined. The threshold levels will vary with specific Arduino implementation, so to learn what they are you should consult the documentation.
+An Arduino digital input is one that responds to two different levels: anything above a certain threshold is considered HIGH, and anything below a certain voltage is considered LOW. Anything in between is not defined. The threshold levels will vary with specific Arduino implementation, so to learn what they are you should consult the documentation.
 <WRAP center round important 60%>
@@ Line 9: / Line 9: @@
 </WRAP>
-Typically, digital input signals are designed so that when HIGH they have a value equal to the supply voltage and when LOW they are equal to 0 volts.
+Digital output signals are typically designed so that when HIGH they have a value equal to the supply voltage and when LOW they are equal to 0 volts.
-We've already seen an example of Arduino digital inputs in the [[arduino:arduino_crash_course:basic_interaction|Basic Interaction]] examples. Here is the TODO but using some additional variable types that better match the role of the variables.
+We've already seen an example of Arduino digital inputs in the [[arduino:arduino_crash_course:basic_interaction|Basic Interaction]] examples. Here is the ''LightSwitchPullup2.ino'' example but using an additional variable type that better matches the role of the ''buttonState'' variable. Variables of type ''boolean'' can store the values ''true'' and ''false''. Since the button has two states, pushed and not pushed, using a variable that can store only two states, ''true'' and ''false'' makes sense. We have chosen to let ''true'' correspond to the button's "pushed" and ''false'' correspond to "not pushed." It is typical for variables used to store digital inputs be of type ''boolean''.
-FIXME with const and boolean
+We have also added the ''const'' modifier to the ''pushButtonPin'' and  ''ledPin'' variables to say that their values won't change in the program. In fact, when you add the ''const'' modifier to a variable declaration, the value of the variable //can't// change.
+<file c LightSwitchPullup2a.ino>
+/*
+ LightSwitchPullup2a
+ Turn an LED on and off.
+ Internal pullup version.
+ */
+const int pushButtonPin = 2;  // connect the push button to digital pin 2
+const int ledPin = 13;        // connect the LED to pin 13
+boolean buttonState;          // stores current button state
+void setup() {
+  pinMode(pushButtonPin, INPUT);  // make the pushbutton's pin an input
+  digitalWrite(pushButtonPin, HIGH);  // turn on internal pullup resistors
+  pinMode(ledPin, OUTPUT);        // make LED's pin an output
+}
+void loop() {
+  buttonState = digitalRead(pushButtonPin);  // read the input pin
+  // set LED state accordingly
+  // note the inverted logic resulting from using pullup resistors.
+  digitalWrite(ledPin, !buttonState);        // turn the LED on or off
+}
+</file>
 ===== Toggling state =====
@@ Line 19: / Line 45: @@
 Below is an attempt to write an Arduino program that //toggles// power to an LED when a button is pressed. In other words, if the pushbutton is pressed while the LED is off, it should turn on; when the pushbutton is pressed again, the LED should turn off.
-To implement this functionality, we must keep track of the state of the program. In particular, in each loop iteration, we will need to know if the button is being pressed and in addition we will need to keep track of whether the button was pressed during the previous time though the loop.
+To implement this functionality, we must keep track of the state of the program. In particular, in each loop iteration, we will need to know if the button is being pressed, and in addition we will need to keep track of whether the button was pressed during the previous time though the loop.
 Our first attempt at writing the program is below. Be cautioned that it won't work as expected. It is logically correct, but it doesn't account for a physical characteristic of real-world switches. We will address this problem and its solution in the next section.
@@ Line 44: / Line 70: @@
   boolean buttonState = digitalRead(pushButtonPin);  // read the input pin
-  // if button goes down and before it was high
+  // if button goes down and previously it was high...
   if (buttonState == LOW && lastButtonState == HIGH) {
     if (ledState == HIGH)            // toggle LED
@@ Line 53: / Line 79: @@
     digitalWrite(ledPin, ledState);  // turn the LED on or off
   }
   lastButtonState = buttonState;
 }
@@ Line 62: / Line 88: @@
 ==== Software debouncing ====
-A very simple approach debouncing is to introduce a delay whenever a relevant switch press is detected. The amount of delay will vary from switch to switch, so experimentation will likely be required.
+A very simple approach to fixing the debouncing problem in software is to introduce a delay whenever a relevant switch press is detected. The delay must be greater than the time it takes for the switch to settle and will vary from switch to switch, so experimentation will likely be required.
-FIXME general
-FIXME add pind number to debounce function
 <file c LightToggleDebounced.ino>
@@ Line 81: / Line 103: @@
 boolean lastButtonState = HIGH; // value of buttonState from previous loop iteration
 boolean buttonState = HIGH;
+boolean debounce(int pinNum) {
+  delay(debounceTime);
+  return digitalRead(pinNum);
+}
 void setup() {
@@ Line 87: / Line 114: @@
   pinMode(ledPin, OUTPUT);            // make LED's pin an output
   digitalWrite(ledPin, ledState);
-}
-boolean debounce(boolean lastState) {
-  boolean nowState = digitalRead(pushButtonPin);
-  if (lastState != nowState) {
-    delay(debounceTime);
-    nowState = digitalRead(pushButtonPin);
-  }
-  return nowState;
 }
 void loop() {
-  buttonState = debounce(lastButtonState);  // read the input pin
+  buttonState = debounce(pushButtonPin);  // read the input pin
-  // if button goes down and before it was high
+  // if button goes down and previously it was high...
   if (buttonState == LOW && lastButtonState == HIGH) {
-    buttonState = digitalRead(pushButtonPin);
     ledState = !ledState;
   }
@@ Line 113: / Line 129: @@
 </file>
-More elaborate debouncing techniques have also been used. For example, you can measure the time between HIGH-to-LOW or LOW-to-HIGH transitions and when they have gotten long enough you can assume that the switch is no longer bouncing. We leave the reader to research and explore these.
+More elaborate debouncing techniques have also been used. For example, you can measure the time between HIGH-to-LOW or LOW-to-HIGH transitions and when they have gotten long enough you can assume that the switch is no longer bouncing. We leave it to the reader to research and explore these.
-=== Using a user-defined function ===
+=== User-defined functions ===
-The the example above places the switch reading and debouncing code into its own **function**. One advantage of doing this is that it creates more clarity in the code by allowing us to give a good name to the process it encapsulates. Another reason is that it makes it easier to change and experiment with different algorithms for, in this case, debouncing. Yet another reason is that it gives you a clear block of code that you can re-use in other projects.
+The the example above places the switch reading and debouncing code into its own **function**. One advantage of doing this is that it creates clarity in the code by allowing you to give a good name to the process you have encapsulated. Another reason is that it makes it easier to change and experiment with different algorithms for, in this case, debouncing. Yet another reason is that it gives you a clear block of code that you can re-use in other projects.
 ==== Hardware debouncing ====
@@ Line 126: / Line 142: @@
 ===== Multiple state =====
-(multiple lights on/off)
+The example above is a program that is essentially in of two states: the LED is on or off. Below are two examples where the program has multiple states. The first is a timer-driven and the second a push-button driven three-light blinky-thing.
+<file c MultipleLEDsTimer.ino>
+/*
+ MultipleLEDsTimer
+ Cycle through three LEDs with a timer.
+ */
+const int delayTime = 500;  // time to wait between LED changes
+const int led0 = 13;        // connect an LED to pin 13
+const int led1 = 12;        // connect an LED to pin 12
+const int led2 = 11;        // connect an LED to pin 11
+int ledState;               // used to decide which LED is on (0 to 2)
+void setup() {
+  // make LED pins outputs
+  pinMode(led0, OUTPUT);
+  pinMode(led1, OUTPUT);
+  pinMode(led2, OUTPUT);
+  // initialize state
+  ledState = 0;
+  // turn the correct LED on and the others off
+  digitalWrite(led0, HIGH);
+  digitalWrite(led1, LOW);
+  digitalWrite(led2, LOW);
+}
+void loop() {
+  delay(delayTime);
+  ledState = (ledState + 1) % 3;    // cycle through 0,1,2
+  // turn the correct LED on and the others off
+  if (ledState == 0)
+  {
+    digitalWrite(led0, HIGH);
+    digitalWrite(led1, LOW);
+    digitalWrite(led2, LOW);
+  }
+  else if (ledState == 1)
+  {
+    digitalWrite(led0, LOW);
+    digitalWrite(led1, HIGH);
+    digitalWrite(led2, LOW);
+  }
+  else if (ledState == 2)
+  {
+    digitalWrite(led0, LOW);
+    digitalWrite(led1, LOW);
+    digitalWrite(led2, HIGH);
+  }
+  else // turn all LEDs on to indicate an error state.
+  {
+    digitalWrite(led0, HIGH);
+    digitalWrite(led1, HIGH);
+    digitalWrite(led2, HIGH);
+  }
+}
+</file>
+<file c MultipleLEDsPushButton.ino>
+/*
+ MultipleLEDsPushButton
+ Cycle through three LEDs with a pushnutton
+ */
+const int pushButtonPin = 2;  // connect the push button to digital pin 2
+const int led0 = 13;          // connect an LED to pin 13
+const int led1 = 12;          // connect an LED to pin 12
+const int led2 = 11;          // connect an LED to pin 11
+const int debounceTime = 5;     // number of millisecods to delay after button press
+int ledState;                   // used to decide which LED is on (0 to 2)
+boolean lastButtonState = HIGH; // value of buttonState from previous loop iteration
+boolean buttonState = HIGH;     // start by assuming button is unpressed
+boolean debounce(int pinNum) {
+  delay(debounceTime);
+  return digitalRead(pinNum);
+}
+void setup() {
+  pinMode(pushButtonPin, INPUT);      // make the pushbutton's pin an input
+  digitalWrite(pushButtonPin, HIGH);  // turn on pullup resistors
+  // make LED pins outputs
+  pinMode(led0, OUTPUT);
+  pinMode(led1, OUTPUT);
+  pinMode(led2, OUTPUT);
+  // initialize state
+  ledState = 0;
+  // turn the correct LED on and the others off
+  digitalWrite(led0, HIGH);
+  digitalWrite(led1, LOW);
+  digitalWrite(led2, LOW);
+}
+void loop() {
+  buttonState = debounce(pushButtonPin);  // read the input pin
+  // if button goes down and previously it was high...
+  if (buttonState == LOW && lastButtonState == HIGH) {
+    ledState = (ledState + 1) % 3;    // cycle through 0,1,2
+  }
+  // turn the correct LED on and the others off
+  if (ledState == 0)
+  {
+    digitalWrite(led0, HIGH);
+    digitalWrite(led1, LOW);
+    digitalWrite(led2, LOW);
+  }
+  else if (ledState == 1)
+  {
+    digitalWrite(led0, LOW);
+    digitalWrite(led1, HIGH);
+    digitalWrite(led2, LOW);
+  }
+  else if (ledState == 2)
+  {
+    digitalWrite(led0, LOW);
+    digitalWrite(led1, LOW);
+    digitalWrite(led2, HIGH);
+  }
+  else // turn all LEDs on to indicate an error state.
+  {
+    digitalWrite(led0, HIGH);
+    digitalWrite(led1, HIGH);
+    digitalWrite(led2, HIGH);
+  }
+  lastButtonState = buttonState;
+}
+</file>
+===== Switch-case selection structure =====
+Both examples above use the //nested if-else// selection structure. Arduino's programming language also includes another selection structure that is useful in these situations: the //switch-case// structure. Below we have rewritten MultipleLEDsPushButton to use a //swich-case// structure.
+<file c MultipleLEDsTimer2.ino>
+/*
+ MultipleLEDsTimer2
+ Cycle through three LEDs with a timer.
+ This version uses a switch-case selection structure.
+ */
+const int delayTime = 500;  // time to wait between LED changes
+const int led0 = 13;        // connect an LED to pin 13
+const int led1 = 12;        // connect an LED to pin 12
+const int led2 = 11;        // connect an LED to pin 11
+int ledState;               // used to decide which LED is on (0 to 2)
+void setup() {
+  // make LED pins outputs
+  pinMode(led0, OUTPUT);
+  pinMode(led1, OUTPUT);
+  pinMode(led2, OUTPUT);
+  // initialize state
+  ledState = 0;
+  // turn the correct LED on and the others off
+  digitalWrite(led0, HIGH);
+  digitalWrite(led1, LOW);
+  digitalWrite(led2, LOW);
+}
+void loop() {
+  delay(delayTime);
+  ledState = (ledState + 1) % 3;    // cycle through 0,1,2
+  // turn the correct LED on and the others off
+  switch (ledState) {
+    case 0:
+      digitalWrite(led0, HIGH);
+      digitalWrite(led1, LOW);
+      digitalWrite(led2, LOW);
+      break;
+    case 1:
+      digitalWrite(led0, LOW);
+      digitalWrite(led1, HIGH);
+      digitalWrite(led2, LOW);
+      break;
+    case 2:
+      digitalWrite(led0, LOW);
+      digitalWrite(led1, LOW);
+      digitalWrite(led2, HIGH);
+      break;
+    default:
+      digitalWrite(led0, HIGH);
+      digitalWrite(led1, HIGH);
+      digitalWrite(led2, HIGH);
+      break;
+  }
+}
+</file>