Introduction

If you’ve gone through the Arduino Pin by Pin tutorial, you’ve already used the Arduino IDE (Integrated Developing Environment). Understanding how to manipulate the hardware side of things using code is the key to using the UNO as a sensing platform. As programming is better “learned” than “taught” we’ll just jump in straight away^11 If you’re experienced in programming, you can pretty much skip everything in this document. Even so, make sure that you do understand the peculiarities of programming for microcontrollers vs. fully fledged computers!

My First Error Message

First things first, open up the Arduino IDE (version 3). Connect the UNO and select in the IDE using Tools->Port->your UNO port . Hopefully on your screen you’re seeing the code below

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

The comments^22 Comments start with two forward slashes (//) and are not evaluated, they’re there only to explain parts of code, sprinkle comments liberally within your code so that other people (and future you) can understand what’s going on explain the basic structure of our code very well. The setup chunk runs only once and anything in the loop section runs repeatedly.

As an example project we’ll be combining the PWM feature of the UNO and the Analog inputs to make a dimmable LED. A good way to start out is to write down, in broad terms, what we’ll need to code for this to work.

• Read the voltage at an analog pin.
• Write the same value to an PWM pin

The wiring will look like this, use a 100-200 ohm resistor to limit LED current also watch out for LED polarity.

So lets be direct and write what we want down. Maybe the IDE is smart enough to parse English.

void setup() {
  
  Set pin A0 as input, set pin 3 as output.
}

void loop() {
  
  Read pin A0 adjust pin 3 accordingly
}

Copy this in and press the uplad button (arrow on the top left corner). A second later you should get an error message at the bottom that reads like this.

Users/Emre/Documents/Arduino/sketch_sep10b/sketch_sep10b.ino: In function 'void setup()':
sketch_sep10b:3: error: 'Set' was not declared in this scope
   Set pin A0 as input, set pin 3 as output.
   ^
/Users/Emre/Documents/Arduino/sketch_sep10b/sketch_sep10b.ino: In function 'void loop()':
sketch_sep10b:8: error: 'Read' was not declared in this scope
   Read pin A0 adjust pin 3 accordingly
   ^
exit status 1
'Set' was not declared in this scope

Not great, we seemed to have made a couple of mistakes. Lets fix them!

The “Right” Way

The error we got told us that ‘Set’ was not declared in this scope. We didn’t really expect the code to work (mainly because it wasn’t code) but it’s interesting nevertheless, that the IDE tells us that the reason it stopped was it couldn’t find ‘Set’ the first word of code we wrote in this sketch. Error messages can be very useful, to understand what it meant google “was not declared in this scope + arduino” and look at the first couple of links.

It should not come as a surprise, whereas we were using human language, the IDE^33 Rather the compiler was expecting Arduino language. Arduinos are programmed in a subset of C/C++ languages, custom fit to be compatible with the little microcontroller.

To get a good overview of the language and a nice start, read through this document. I’ll repeat some parts here so don’t worry if you don’t understand it all.

Lets have a look at the “right” code44 Invariably, there are millions of ways to achieve the same thing with code, the snippets you see here will not necessarily be the “best” way of doing things. If you can spot something that can be improved, improve it!

void setup() {
  
  //Set pin A0 as input
  
  pinMode(A0, INPUT);
  
  /*Every declaration or function call in C is ended with a semicolon,
  this is our way of telling the compiler that our sentence is over,
  and it might parse it to make it machine readable.
  
  Note the curly brackets, they indicate a "chunk" of code, 
  the internals of a function or a loop. Where the setup() function ends with the bracket
  loop() begins*/
    
  
  //set pin 3 as output
  
  pinMode(3, OUTPUT);
  
  /* Before using the pins as input or output,
  we have to make sure that UNO knows our intention beforehand.
  pinMode function lets us tell the UNO which pin is going to be used as input or output. 
  The parantheses after pinMode signify that this is a function call.
  pinMode function is a basic functon that was written by the Arduino developers.
  Functions keep us from reinventing the wheel while programming. 
  
Haiku
  Any function must end,
  with parantheses. Inside,
  lie the arguments.

  The values "3" and "OUTPUT" in the parantheses are the arguments of this function. 
  Order of arguments matter */
    
}

void loop() {
  
  int x =0;
  
  /* We have declared a variable named x, and assigned the value 0 to it.
  int suggests that the variable is going to be an INTeger.
  A declaration is what the name suggests.

Tanka
  We have declared that,
  We will need an integer, 
  The name will be x,
  and the value, just zero.
  And it ends, semi-colon.

  Any time we type x, we will be referring to this variable.
  = is the assignment operator.
  It is good practice to assign a value when we declare a variable.*/
  
  x=analogRead(A0);
  
  /* Another function, you should remember analogRead from the previous tutorial.
  We have given the A0 pin as its argument. 
  The function will read the A0 value using the ADC.
  The read value will be returned and stored in x.
  Note the lack of "int", as we have declared the value before. 
  
Haiku
  To read a signal,
  And to store it in x too,
  No int, just equals.*/
  
  x=x*(255.0/1023.0);
  
  /* If you check the documentation for analogRead and analogWrite, (use Google)
  you can see that analogRead returns a value between 1023 and 0.
  analogWrite takes an argument in the range 0 to 255, 
  we rescale x to fit in the analogWrite range. 

Haiku
  a function, to work,
  needs more than just a name. check
  documentation.*/
  
  
  analogWrite(3,x);
  /*This time we write the rescale x value to pin 3 as a PWM signal,
  the brightness of the LED will change as the PWM value changes.
  
Tanka
  read a value and,
  modify it. line of code.
  with analogWrite,
  dim. light emmiting diode.
  zen? pulse width modulation.*/
}

In short, it takes just 5 lines of code to get this working. If anything is not clear, go back and read the linked pdf at the beginning of this chapter.

void setup() {
  
  //Set pin A0 as input
  pinMode(A0, INPUT);
  //set pin 3 as output.
  pinMode(3, OUTPUT);
}

void loop() {
  
  int x = analogRead(A0);
  //Read the voltage from potentiometer. Declaration and assignment in a single line
  x=x*(255.0/1023.0);
  //Scale appropriately
  analogWrite(3,x); 
  //Write value to pin 3, PWM output.
}