How to Code Arduinos




So I was looking through the help section of the community when I noticed some people where having trouble with coding Arduinos, so I'm making this to help.

For this Instructable you will need:


Arduino IDE

Some parts of this may be different for 3.3v Arduinos, i use a 5v Arduino so i will be teaching according to that.

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Step 1: Input Commands

Here where gonna look at Input Commands. There are two main types of pins on the Arduino, Digital I/O(Input/Output) and Analog Input, the Digital pins can be both Inputs and Outputs, and the Analog pins are special inputs that can detect the current Voltage.


Before we can use any sensors or actuators we need to tell the Arduino what pins they are on.

int sensorPin = A1;

Void setup(){
pinMode(sensorPin, INPUT);

This tells the Arduino that there is a input on pin sensorPin, which is a integer standing for the number A1. The reason we do this is because if we need to change the pin number for some reason, we can change it in the one place at the top instead of going trough the entire code and having to change the number every time its referenced.This command goes in Void setup, most commands go in Void loop so put them there unless told otherwise.

Digital Read

This is the most basic way to input into a Arduino. The signal well either be On or Off, this is used for detecting the state of a light switch or button. Here is how to use it.

int DsensorVal = digitalRead(DsensorPin);

This assigns int DsensorVal to equal what DsensorPin is picking up. In this case it will be a 1 or 0, On or Off.

Analog Read

The Analog Read command is for detecting voltage on one of the Analog pins of the Arduino. This is used to connect to any sensor that gives off a voltage as data, such as a Light Dependent Resister, Trimmer pot, some Temperature sensors, etc.

Int AsensorVal = analogRead(AsensorPin);

This assigns int AsensorVal to the voltage on AsensorPin. this will be a value between 0 and 1023, according to a voltage between 0 and 5 volts, ex. 1.25v = 256, 2.5v = 512, 3.25v = 768.

We'll see how to use these in the Next Step.

Step 2: How to Use Input Values

Now that we have values from our sensors lets see how to use them.


Yes i said IF, the IF command is the most important command of all. It is the main bridge between our actuators and sensors. Here's how it's used.

if (a == b){
action here(We'll discuss this in the next step)

The brackets is where we will place the code we want to run. The == means equal to, this has to be two equals because only one would make a = b and make it always true. The == can be replaced any one of the following,

  • != not equal
  • > greater then
  • < less then
  • >= greater then or equal to
  • <= less then or equal to

So IF a == b then we run the brackets. We can also have more then one Criteria to fulfill

if ((a == b) && (a < c)){

Now we added the && which means AND, so as long as a == b AND a < c, the IF statement will run the code. we can also use || (OR) and ! (NOT) in the place of && to get the appropriate response.

That is the most basic and most used Control command. We can take this command one step further by adding a ELSE to it. This makes it so that when IF is not active the ELSE is.

if (a == b){

Now anything in the ELSE brackets will be run when IF is negative.


So the way we use the digital input is like this.

If (DsenserVal == 1){

1 is the same as writing HIGH. So when there is 3-5volts placed on DsenserPin, the action you have set will happen. sometimes buttons are set in reverse, so that it equals 0 when the button is pressed, if so just change the 1 to a 0 and it will work.


This is where it gets fun.

We have the normal if command.

if (AsensorVal < 500){

Where IF is checking the value of AsensorVal and reacting to it, analog signals are more meant to be used to edit the response of a robot instead of making it respond. We also have a couple commands to edit the signal so its better for end use.


The map command is useful when you need to change the number for a certain range. So say I have a int value that is going to be between 300 and 500, and i want to use it to control a servo that goes 180 degrees, well i can use the command like this

AsensorVal = map(AsensorVal, 300, 500, 0, 180);

Now the value is a number from 0 to 180 that is prepositional to the difference of 300 to 500. So think of a line that is 200 units long, this changes it so the line is the same length but now is only 180 units long. This takes a lot of complex math, but the good folks behind Arduino have made it easy.


This one makes the number have to stay in certain bounds. So if i set it up like this.

AsensorVal = map(AsensorVal, 0, 180);

It now will only allow AsensorVal to be between 0 and 180, if it is lower then 0 then it turns it into 0, if it's above 180 it will change it to 180, these numbers are the min and the max that it can be.

Let's go see how to use Actuators in the next Step.

Step 3: Actuators

So you want to see how to use actuators, well your at the right Step.


yes where using PinMode again, but this time where using it to register a OUTPUT.

void setup(){
pinMode(actuatorPin, OUTPUT);

Now we have declared ActuatorPin a output, so now we can use it as one. This goes in the Void setup.


I wasn't going to leave servos out don't worry. Servos require a little more setup but its still easy.

#include <Servo.h>

Servo myServo;    # Makes a servo object

Int servoPin = 9;     # The number for this has to one of these pins, 11, 10, 9, 6, 5, 3.

Void setup(){
myServo.attach(servoPin);     # Attaching the servo to servoPin, which is equal to 9;

So first we import the servo library, and then we make the object myServo. Then we make a int that is equal to the pin we want to place it on. This has to be a special pin that supports PWM which are marked on the Arduino board. We then attach myServo on the pin we set eariler. Put the attach command in Void setup.

now that we got those setup, lets look at actual outputting signals.


This is the basic On/Off output you'd use to control a LED, Reley, and anything else that is either On or Off.

digitalWrite(actuatorPin, HIGH);

Now actuatorPin is set to High, so anything on it will start to run. To turn it off we use.

digitalWrite(actuatorPin, LOW);


The AnalogWrite command is used to control Motor Speed, LED Brightness, etc. Now most Arduinos dont have actual Analog outputs, but they are able to mimic it. They have special Pins that are PWN(Pulse Width Modulated) that impersonate an analog pin. We control it like this

analogWrite(actuatorPin, Amount);

actuatorPin is the pin the actuator is on. Amount can be a number between 0 and 255.


Let's use some servos.


First we tell what servo, in this case myServo. Then we say write with a value between 0 and 180. and just like that your moving servos.

Step 4: Debug

Its vary important to be able to debug a script. The way to do this is by setting up a serial connection with the Arduino then having it tell when it gets to certain points. You open the Serial monitor by going into the IDE and pressing the button in the upper right with the magnifying glass on it.


first step would be starting our Serial connection like this


This goes in Void setup. The number is the Baud Rate, just leave it at 9600 for now.


Here is how we print in inputs

Serial.print("Hello world");

The first one prints Hello World into the serial monitor. The second prints the value of our Analog Input.


Serial.println is the same as Serial.print but it starts a new line with it. So, for example. If I keep printing in 3 with the Serial.print command, it will receive it as 333333333333. Now if we use the Serial.println to print it in, it will recieve it as




get the idea.

Step 5: Example

Here I'll show you a script that shows everything we learned. If you want to build it follow the schematic at the top. The Potentiometer on the left is pot1 and controls the servo, the one on the right it pot2 and controls the brightness of the LED. The Button controls whether the LED is on or off.

#include <Servo.h>

Servo myServo;		// Registering our Servo

int servoPin = 9;	// The Pin our Servo is on
int lightPin = 3;	// The Pin our LED is on
int potPin1 = A1;	// The Pin our Potentiometer that controls the Servo is on
int potPin2 = A0;	// The Pin our Potentiometer that controls the LED is on
int buttPin = 6;	// The Pin our Button is on

void setup(){
	myServo.attach(servoPin);	// Attaching our servo
	pinMode(lightPin, OUTPUT);	// Registering our LED Pin as a Output
	pinMode(potPin1, INPUT);	// Registering our Servo Potentiometer Pin as a Input
	pinMode(potPin2, INPUT);	// Registering our LED Potentiomerer Pin as a Input
	pinMode(buttPin, INPUT);	// Registering our Button Pin as a Input
	Serial.begin(9600);		// Starts the Serial communacation

void loop(){
int pot1Val = analogRead(potPin1);		// Gets Pot1's current value
pot1Val = map(pot1Val, 200, 823, 0, 180);	// Mapping it so that it removes the beginning and the end of the Pots range
pot1Val = constrain(pot1Val, 0, 180);	// Insures that the Servo Input stays between 0 and 180
myServo.write(pot1Val);				// Makes the servo move to the current location
Serial.print("Pot1 value is: ");		// Starts printing in Debug Info
Serial.println(pot1Val);			// It's now set up so it will say "Pot1 value is: (Current Value)"

int pot2Val = analogRead(potPin2);		// Gets Pot2's current value
pot2Val = map(pot2Val, 0, 1023, 0, 255);	// Maps it accordingly
Serial.print("Pot2 value is: ");		// starts printing in Debug Info
Serial.println(pot2Val);			// It will say "Pot2 value is: (Current Value)"

int button = digitalRead(buttPin);		// Gets the state of the Button

if(button == 1){				// The way the buttons is set up, 1 means it is being pressed
	analogWrite(lightPin, pot2Val);		// If its true then turn on the led at this brightness
else{						// Else
	digitalWrite(lightPin, LOW);		// If ELSE is true, which means IF is false, then turn off led

delay(50);					// Makes a small delay so it isn't running every millisecond.

Step 6: Thanks

Without further ado i must bid you good bye and thanks for reading. I hope the information in here made sense.

If you have any questions please ask in the comments below, if you have any suggestions either comment ||(or) message me at my instrucatables account.

Please vote for me in the Sensors Contest

It would be much appreciated and vary encouraging.

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    30 Discussions


    1 year ago on Step 5

    why are we using constrain for the pot1val's value for servo functions , while we didn't use constrain for the LED?

    2 replies

    Reply 1 year ago

    First off, thanks for reading, no on to the answer. All the ADCs on the uno return a 10bit value which is a number 0-1023. I have the servo mapped to make a number between 200-820 correlate to a number 0-180 but if the value is over 820 the mapped value will be over 180. Same for the lower value. So I contstrained pot1val to make sure it stayed between 0-180 because it is likely to be higher or lower. Pot2val on the other hand it going from the max and min that the analog value can be so the value can't be out of range for the output value I want.

    Did that answer your question?


    1 year ago

    This helped me a lot :)


    1 year ago

    Hello supernoodle2014 ,

    As I am a beginner on Arduino, my project is about a pill reminder, But when I try to upload the code for the project it doesn’t work not verified on Arduino software and always a wrong message showed up.
    "I copy and paste it on Arduino software"

    also hen I build the circuit and for connection need I add I2c for LCD, but this code I will attach doesn't have a code foe i2c because as I think when i add i2c to the circuit I need other code for it but I don't know how to connect two codes together or no need for it?

    could you please check the code what is wrong on it and how to add another code for i2c ?

    10 replies

    Reply 1 year ago

    I couple questions, is this your code? why do you need to add an i2c LCD into the code? what error does it give you?


    Reply 1 year ago

    No this is not my code, I had it from internet since I didn’t know how to build a code.
    And I add I2c for the connection for LCD keypad in order to connect it with Arduino board as I will add another part like LED, buzzer and photoresistor. The wrong in the code first whenever I run it on Arduino software a problem in library shows as “#include ”
    you could check it copy it and paste in Arduino to see that I tried different way but I don’t know. I need your help to see the code and tell me how to fix it and how to make it fit with my LCD keypad ?
    Or if it possible could you build a code for me please I struggle on that ?


    Reply 1 year ago

    So the error I have is a that I'm missing a library called MenuBackend. This is a menu library that I can't find a download for, but I did find the github so just have to coby all the text from GitHub and set it up into a file. I'll see if I can find a LCD library that is drop in compatable with the normal library. Could you give me a schematic of your project so I know how everything's connected?


    Reply 1 year ago

    yes the error missing a library called MenuBackend "Error compiling for board Arduino Nano" that I can not figure it out how to slove it. unfortunately we did not have a schematic.

    okay I will upload for you the website in order to see the project. we used all the same part list but we change LCD to LCD keypad and use more component a buzzer and I2c for connection.

    the project I made is about pill reminder the code should achieve on lcd keypad shows the name of medicine and can set time using keypad and RTC for when to take each does, when the time come such as 3 o’clock a led and buzeer should work to notify and a photoresistor will be down at each bottle.
    here is it
    Could you please help be connect buzzer and I2c add to the code if you find what’s wrong on it ? Because I have struggle on code.

    so could you change the code for LCD and add buzzer and I2c please if as you said you know what is wrong on it if would not bothers you I will much appreciate it ...


    Reply 1 year ago

    Here is a photo of LCd and i2c


    Reply 1 year ago

    Could I have a link to the LCD and one for the LCD controller. Is there anything else your going to add to it?


    Reply 1 year ago

    For LCD

    But for LCD Controller is fixed as I understand with LCD together.

    For the components yes nothing else.
    Parts list:
    red LED (3x)
    510 ohm resistors (3x)
    2.2 kohm resistors (3x)
    photoresistors (3x)
    Sparkfun Real Time Module (1x)
    Arduino uno(1x)
    LCD Keypad Shield (1x)
    buzzer (1)


    Reply 1 year ago

    I got a zip file attached if it works properly. The folder called
    sketch_april20a needs to go in your sketches folder and the other two
    folders need to go in libraries. I compiled it and it says it worked so
    now it just needs to be tested.


    Reply 1 year ago

    thank you I solved it but another problem on the code is shown. I upload 2 files for LCD with I2c and

    I change LCD to LCD with i2c and solve the error for MenuBackend.h by upload library for both.

    and then another problem shown in the code after the first one is solved here is it

    no match for 'operator==' (operand types are 'const char*' and 'MenuItem')

    if(newMenuItem.getName()== menu.getRoot()){


    exit status 1
    no match for 'operator==' (operand types are 'const char*' and 'MenuItem')

    for using the Sparkfun real time clock module I will post a picture. and as I just realized today the RTC I'm using is different than the one in the code!

    I will upload you the code and the 2 new library a download as a zip files. could you please check them and help me as soon as possible with RTC and the error in the code please. I'm looking forward for your answer as soon as possible.


    Reply 1 year ago

    Did you try it with the files I gave you? The menuBackend Master library I gave you has been edited to add the function getRoot.


    3 years ago

    thank you! it's very useful considering I'm trying to find more resources to strengthen my grip on programming arduino. maybe you can make more guides for programming arduino like explaining what certain functions are used for. maybe it'll help tons for beginners like me. again, thank you

    3 replies

    Reply 3 years ago

    Thanks for reading. are there any particuler functions you would like to know about?


    Reply 3 years ago

    thank you for replying. I'm actually wondering how does string function works in arduino and how can I apply in motor control application. thanks again


    Reply 3 years ago

    are you asking about the String function and how to control a motor, or how to use the String function to control a motor.