In this lab, we’ll be adding two pushbuttons to the previous lab and using them to affect the output conditionally. (i.e. according to various rules)

We’re now using button 1, on pin 2, and button 2, on pin 3.

Background

In Conditional Logic, the goal is to make decisions based on information, rather than blindly doing the same thing over and over. In C++, there are a variety of logical operators. Here, we’ll look at a subset of those known as relational operators.

== equal to
!= not equal to
<  less than
<= less than or equal to
>  greater than
>= greater than or equal to

Each of these is used in conjunction with two expressions. Let’s look at an example:

int button1Pushed = digitalRead(2);
int button2Pushed = digitalRead(3);

//we're going to use this integer to count how many buttons are pushed.
int numButtonsPushed = button1Pushed + button2Pushed; 

if (numButtonsPushed == 2) // "if numButtonsPushed is equal to 2"
{
    // do some stuff only if both buttons are pushed
}
else if (button1Pushed) // "if button 1 is pushed"
{
    // do some stuff if button 1 is pushed
}
else if (button2Pushed) // "if button 2 is pushed"
{
    //do something if button 2 is pushed
}
else if (analogRead(0) <= 500) // "if analogRead(0) is less than or equal to 500"
{
    // do some stuff if the potentiometer is less than about halfway
}
else
{
    // do some stuff if no button is pushed
}

These relational operators allow your code to make decisions and therefore behave differently in different circumstances.

The Lab (Part 1)

In part 1, we’re going to use basic conditional logic to change the behavior of our system from the previous lab. At the end of the last lab, we were taking the analog value, dividing it by 40, and then adding 20 to it. Let’s do the math! The range of the analog input is normally 0 <= x <= 1023, where x is the current value of the analogRead() function.

(0 <= x <= 1023) / 40 becomes 0 <= x <= 25, mathematically. If we do (0 <= x <= 25) + 20, we get 20 <= x <= 45 as the range of our analog input after the math.

So, taking our loop code from last lab, let’s calculate our analog value (analogRead(A0) / 40 + 20) and then use that as part of a conditional statement. In the last lab, we were turning both the LED and the Piezo “on”, waiting 10ms, and then turning both off again and waiting by a number of milliseconds equal to the calculated analog value. Let’s move that code inside an if statement. Let’s start out by saying if the calculated analog value is greater than or equal to 30, then we want to use the LED and the Piezo. This way, if the value is less than 30, we won’t hear any buzzer or see the LED flashing.

The next thing we want to do is add an else if to our if statement. What we’re going to do is make the LED blink at a steady rate of twice per second if the analog value wasn’t greater than or equal to 30, and if button 1 is pushed. Remember, statements inside an else if block will only execute if their condition is true and if the previous if block did not execute, so we won’t need to refer to the analog value at all in our else if block. Got it? Also, remember digitalRead is the function that we use to read buttons and other digital values.

Logical Conjunction Example

Just like in English, programming has conjunctions too. In English, we might say “if this and that, then do this.” In C++, we have two primary logical conjunction operators: && which means “and”, and ||, which means “or.”

So, in an if statement, we can string multiple conditionals together to have more control.

  if (numButtonsPushed == 1 && analogRead(0) > 500)
  {
      // some code that runs if only one button is pushed AND analog input 0 is reading greater than 500.
  }
  else if (numButtonsPushed == 2 || analogRead(0) < 100)
  {
      // some code that will run if both buttons are pushed OR if analog input 0 is less than 100
  }

The Lab (Part 2)

In this part of the lab, we want to make use of Logical Conjunction to make our Arduino do things it couldn’t do before. Simply put, we want to see you implement the following scenario:

if button 1 is being pushed AND the calculated analog value is greater than 35, then blink the LED at the same time that we’re toggling the Piezo element (i.e. both are going on and off at the same time). else, we want to toggle just the Piezo element. This way, the user can push button 1 when they would like to see the timing of the toggling displayed visually, but we “protect” them from it blinking too fast.

The final thing we want to do is change it so that there is a third conditional in that if statement. if button 2 is being pushed, we want to blink the LED no matter how fast it is going, and we also don’t care if they’re pushing button 1. So, if ((conditional1 && conditonal2) || conditional3) is essentially what it will look like.

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