Category Archives: Tutorial

One of my biggest frustrations in programming is the confusion over inputting data over the serial port. There are lots of Arduino tutorials that make it much harder than it has to be. There are many difficult and complicated ways you can read data over the serial port, but luckily there is an easy way. While we touched on this briefly in earlier videos, it is such an important topic I want to focus on it in this lesson.

In order to read data over the serial port, you first have to determine what type of data you will be expecting. Almost all possible needs can be covered by three simple data types. Usually you can make just about any project work with Strings, Float’s, or Int’s. So, you need to know how to read these three data types over the serial port. The easiest way to read a string of text is using the Serial.readString() command. The easiest way to read a Float is with the Serial.parseFloat() command and the easiest way to read in Int with with the Serial.parseInt() command.

To practice this, lets do the following. Write a program that will promt the user for his age, for how much he weighs, and then how tall he is in feet. Then print out a nicely formatted output that relays that information back to the user.

In order to do this the first thing we must do is decide what type of variables to use for each of these three pieces of data. For the person’s name, you naturally would use a String, since a name is a string of text. To store the weight, we would just about always round to the nearest whole number so it would make sense to use an Int for this. On height, we would not normally round to the nearest foot . . . we might want to say that someone was 5.5 feet tall. In this case we should use a float, since we want the decimal numbers. So, we would then declare these variables the suitable type and then read them in using the corresponding commands.

Also, remember when you are going to read data from the serial port you must do three things: 1) Prompt the user for data, 2) wait for him to input the data, and 3) read the data. This should be review as we have done this in several earlier lessons.

Try and write the program yourself, but if you get stuck you can look at the code below that I wrote for this problem.

String myName;   //Declare a String variable to hold your name
int age;         //Declare an Int variable to hold your age
float height;    //Declare a float variable to hold your height

void setup() {
  Serial.begin(9600);      // turn on Serial Port
}

void loop() {
  
  Serial.println("Please enter your name: "); //Prompt User for input
  while (Serial.available()==0) {             //Wait for user input
  
  }
  myName=Serial.readString();                 //Read user input into myName
  
  Serial.println("How old are you? ");        //Prompt User for input
  while (Serial.available()==0)  {
  
  }
  age=Serial.parseInt();                      //Read user input into age
  
  Serial.println("How tall are you? ");      //Prompt User for input
  while (Serial.available()==0)  {
  
  }
  height=Serial.parseFloat();                //Read user input into height
  
  Serial.print("Hello ");                    //Print out nicely formatted output.
  Serial.print(myName);
  Serial.print(", you are ");
  Serial.print(age);
  Serial.println(" years old,");
  Serial.print("and you are ");
  Serial.print(height);
  Serial.println(" feet tall.");
  Serial.println("");
 
}

String myName; //Declare a String variable to hold your name

int age; //Declare an Int variable to hold your age

float height; //Declare a float variable to hold your height

void setup() {

Serial.begin(9600); // turn on Serial Port

}

void loop() {

Serial.println("Please enter your name: "); //Prompt User for input

while (Serial.available()==0) { //Wait for user input

}

myName=Serial.readString(); //Read user input into myName

Serial.println("How old are you? "); //Prompt User for input

while (Serial.available()==0) {

}

age=Serial.parseInt(); //Read user input into age

Serial.println("How tall are you? "); //Prompt User for input

while (Serial.available()==0) {

}

height=Serial.parseFloat(); //Read user input into height

Serial.print("Hello "); //Print out nicely formatted output.

Serial.print(myName);

Serial.print(", you are ");

Serial.print(age);

Serial.println(" years old,");

Serial.print("and you are ");

Serial.print(height);

Serial.println(" feet tall.");

Serial.println("");

}

OK, hopefully you were able to get this working. Now time for you to go solo and write a program on your own.

Prompt the user for his name, and his weight in pounds. Then use that to calculate his weight in Ounces, in grams, and in carats. Note, that is carats, like they measure diamonds, not carrots like you eat.

After doing these calculations send a message to the user greeting him by name and telling him is weight in pounds, in ounces, in grams, and in carats.

In order to do this assignment you will have to do some research to figure out how to do the conversions.

Arduino, Tutorial

Lesson 11: Arduino Circuit to Dim LED with Potentiometer

July 9, 2014 admin

Arduino Dimmable LED — Arduino Circuit for Dimming an LED

In Lesson 8 you learned to write analog voltages on the Arduiono, and in Lesson 10 you learned to read analog voltages from the arduino. In this lesson we will combine what you did in lessons 8, 9, and 10 to create an LED with adjustable brightness. The brightness will be set based on the position of the potentiometer. In order to do this, we need to set the potentiometer up as a voltage divider, and we need to drive the LED from one of the analog pins. For this example, I am using pin 9. The circuit schematic I am using is shown below.

LED Arduino Circuit — This Schematic Creates a Dimable LED

In placing the LED into the circuit, remember that you must always put the longer leg towards the positive voltage. In the case above, the longer leg should be connected to the resistor, and the shorter leg connected to ground. Also remember that we are using a 330 ohm resistor in the circuit to limit the current through the LED.

The goal now is to use what you learned in the last three lessons. You will want to read a value from the potentiometer, and then write a voltage to the LED based on the reading from the potentiometer. Remember that when you read an analog voltage between 0 and 5 volts, the arduino will report a number between 0 and 1023, with 0 representing 0 volts, and 1023 representing 5 volts.

Similarly, when you are writing an analog voltage between 0 and 5 volts, you must write a number between 0 and 255. If you write a “0” value, that corresponds to 0 volts. If you write a value of 255, that will output 5 volts. So, you must scale your write values between 0 and 255 to get voltages between 0 and 5 volts.

The tricky thing now is that we want to dim the LED based on what value we read from the potentiometer. If we read a 0 value from the potentiometer, we want to write a value of 0, which corresponds to a voltage of 0. If we read a value of 1023 from the potentiometer, then we will want to write our maximum voltage of 5 volts, which means we need to write a value of 255. Basically, we need to scale our read values, which will be between 0 and 1023 to suitable write values, which should be between 0 and 255.

Like in the earlier lessons, this is a simple linear relationship and allows us to use the skills we have learned in math class. This sheet explains the math:

Linear Equation — We must scale our read values (0 to 1023) to suitable write values (0 to 255).

So, from the math above, we can see that the Write Value that we should write to the LED should be the value that we are reading from the potentiometer X (255/1023).

With the math out of the way we can write the program. This code is designed for the schematic above where the potentiometer center leg is read with pin A0 and the LED is written from pin 9.

int potPin= A0;  //Declare potPin to be analog pin A0
int LEDPin= 9;  // Declare LEDPin to be arduino pin 9
int readValue;  // Use this variable to read Potentiometer
int writeValue; // Use this variable for writing to LED

void setup() {
  pinMode(potPin, INPUT);  //set potPin to be an input
  pinMode(LEDPin, OUTPUT); //set LEDPin to be an OUTPUT
  Serial.begin(9600);      // turn on Serial Port
}

void loop() {
  
 readValue = analogRead(potPin);  //Read the voltage on the Potentiometer
 writeValue = (255./1023.) * readValue; //Calculate Write Value for LED
 analogWrite(LEDPin, writeValue);      //Write to the LED
 Serial.print("You are writing a value of ");  //for debugging print your values
 Serial.println(writeValue);
 
}

int potPin= A0; //Declare potPin to be analog pin A0

int LEDPin= 9; // Declare LEDPin to be arduino pin 9

int readValue; // Use this variable to read Potentiometer

int writeValue; // Use this variable for writing to LED

void setup() {

pinMode(potPin, INPUT); //set potPin to be an input

pinMode(LEDPin, OUTPUT); //set LEDPin to be an OUTPUT

Serial.begin(9600); // turn on Serial Port

}

void loop() {

readValue = analogRead(potPin); //Read the voltage on the Potentiometer

writeValue = (255./1023.) * readValue; //Calculate Write Value for LED

analogWrite(LEDPin, writeValue); //Write to the LED

Serial.print("You are writing a value of "); //for debugging print your values

Serial.println(writeValue);

}

With this code, you should be able to set the brightness from the potentiometer. You read the voltage from the potentiometer and then scale the value you write to the LED based on the reading from the potentiometer.

RESOURCES: On all these lessons I will include resources on where you can purchase the items mentioned in the lecture.

Arduino Microcontroller: You can get a good deal on the arduino on Amazon. Arduinos are open source and many are cheap Chinese knockoffs, so you want to make sure you get an “official” version, which you can at the link above.

Sparkfun Inventor’s Kit: While the bare arduino will get you started, I really suggest getting the Sparkfun Inventor Kit. The projects I will feature in this tutorial set will use the components in this kit, and it is probably cheaper to go ahead and get the kit than to buy the individual components as you go along. The kit is under $100 on Amazon. The sparkfun kits has everything you need including the arduino.

Arduino, Tutorial

LESSON 10: Analog Reads on the Arduino

June 30, 2014 admin

In today’s lesson we will learn how to use the analog pins on the arduino to read voltage values from a simple potentiometer circuit. The anolog pins are the pins marked A0 to A5 on the Arduino Uno. These are the pins that can be used for making Analog Voltage measurements.

The circuit we will be using today is a simple voltage divider using a potentiometer. Lesson 9 gives a description of how the potentiometer works.

Arduino, Tutorial

LESSON 9: Ohm’s Law and Potentiometers

June 30, 2014 admin

In this lesson we take a quick look at Ohm’s Law to understand the relationship between current and voltage.

Arduino, Tutorial

Lesson 8: Writing Analog Voltages in Arduino

June 27, 2014 admin

We have done some pretty cool stuff so far with the arduino. We have learned how to get input from the user, and how to send information to the user. We have learned how to control commands with both for loops and while loops. We are well on our way to building some really powerful projects. The thing is, so far all of our commands to the arduino pins have in effect been to either turn the pin On or turn it Off. That is, when we digitalWrite HIGH or LOW to the pins, we are either turning on the full 5 volts or turning it all the way off. The truth is that most times we want something in the middle. We would maybe want a voltage of 2.3 volts.

The arduino pins with the squiggly line by them are able to write these in between voltages. These are pins 3,5,6,9,10,11 on the arduino uno.

In the world of engineering and electronics, we say that we want an analog voltage. That is, we want to apply any voltage we want, not just 0 or 5. To output an arbitrary voltage between 0 and 5, would issue the arduino an analogWrite command. Unfortunately, the arguments for the analogWrite command are not as simple as telling it a number between 0 and 5. We must give it an integer between 0 and 255. If we issued the command analogWrite(mypin,0), it would apply 0 volts to mypin. If we issued the command analogWrite(mypin,255), it would appy 5 volts to the pin. As you can see, if we gave the command analogWrite(mypin, 127), we would get about 2.5 volts applied to mypin. You can see those are the easy ones, but in order to figure out exactly what value we should use for exactly the voltage we want, we will need to do some math. Remember all the times you had to calculate the equation of a line in math? Well you are going to do it for real now and for a reason. We need to get an equation that will allow us to calculate the Write Value we should use to get the Voltage

Write Values — You will need to choose the correct value between 0 and 255 to get your desired voltage

You can see that you need the equation for the line above. Good news! You have two points so can calculate the equation of the line. The first point is (0,0), that is to say, that if you want a voltage of 0 to be applied to the pin, you should analogWrite the value of 0, as we explained above. The second point is (5,255), that is to say, if you want to apply a voltage of 5 Volts, you should analogWrite the value 255, as explained above. Now we calculate the equation of the line. the slope would be:

m = (y2-y1)/(x2-x1) = (255-0)/(5-0) = 51

OK, now to get the equation of the line we will use the point slope form of a line, and we get:

(y-y1)=m(x-x1)

We can plug in the point (0,0) and get

(y-0) = m(x – 0)

And when we plug in 51 for m we get:

y = 51X

Remember X is the voltage we want, and Y is the value we write, so this equation can be rewritten:

Write Value = 51 X (Desired Voltage)

So, this equation lets us calculate precisely what value we should analogWrite in order to get the voltage we want on the pin. I hope this makes sense. If you are confused watch the video and it will make more sense.

The bottom line is that we can use this equation to calculate the number we should write to get the voltage that we want at a pin.

As an example, if we wanted to get exactly 2 volts, we should write the value 2X51= 102. If we wanted two volts on the pin myPin, we would issue the command analogWrite(mypin, 102).

Now lets start playing around with a circuit. Lets use the circuit we have been using the last few lessons. Hopefully you still have it hooked up, but if you need help we take you through it step-by-step in Lesson 3.

LED Schematic — This circuit will allow you to independently control two Light Emitting Diodes from the arduino microcontroller

Lets start with our code from Lesson 7:

int redLEDPin=9; //Declare redLEDPin an int, and set to pin 9 
int yellowLEDPin=10; //Declare yellowLEDPin an int, and set to pin 10 
int redOnTime=250; //Declare redOnTime an int, and set to 250 mseconds 
int redOffTime=250; //Declare redOffTime an int, and set to 250 
int yellowOnTime=250; //Declare yellowOnTime an int, and set to 250
int yellowOffTime=250; //Declare yellowOffTime an int, and set to 250
int numYellowBlinks; //Number of times to blink yellow LED
int numRedBlinks;  //Number of times to blink red LED
String redMessage="The Red LED is Blinking"; //Declaring a String Variable 
String yellowMessage= "The Yellow LED is Blinking"; //Declaring a String Variable

void setup() {
  Serial.begin(115200);        // Turn on the Serial Port
  pinMode(redLEDPin, OUTPUT);  // Tell Arduino that redLEDPin is an output pin
  pinMode(yellowLEDPin, OUTPUT);  //Tell Arduino that yellowLEDPin is an output pin
  
  Serial.println("How Many Times Do You Want the Red LED to Blink? "); //Prompt User for Input
  while (Serial.available()==0){ }  //Wait for User Input
  numRedBlinks = Serial.parseInt(); //Read User Input

  Serial.println("How Many Times Do You Want the Yellow LED to Blink? "); //Prompt User for Input
  while (Serial.available()==0){ } //Wait for Input
  numYellowBlinks = Serial.parseInt(); //Read User Input
}

void loop() {

  Serial.println(redMessage);
  for (int j=1; j<=numRedBlinks; j=j+1) {     // Start our for loop
    Serial.print("   You are on Blink #: ");
    Serial.println(j);
    digitalWrite(redLEDPin,HIGH); //Turn red LED on
    delay(redOnTime);             //Leave on for redOnTime
    digitalWrite(redLEDPin,LOW);  //Turn red LED off
    delay(redOffTime);            //Leave off for redOffTime
}
  Serial.println(" ");
  Serial.println(yellowMessage);
  for (int j=1; j<=numYellowBlinks; j=j+1) {     // Start our for loop
    Serial.print("   You are on Blink #: ");
    Serial.println(j);
    digitalWrite(yellowLEDPin,HIGH); //Turn yellow LED on
    delay(yellowOnTime);             //Leave on for yellowOnTime
    digitalWrite(yellowLEDPin,LOW);  //Turn yellow LED off
    delay(yellowOffTime);            //Leave off for yellowOffTime
}
Serial.println(" ");
}

int redLEDPin=9; //Declare redLEDPin an int, and set to pin 9

int yellowLEDPin=10; //Declare yellowLEDPin an int, and set to pin 10

int redOnTime=250; //Declare redOnTime an int, and set to 250 mseconds

int redOffTime=250; //Declare redOffTime an int, and set to 250

int yellowOnTime=250; //Declare yellowOnTime an int, and set to 250

int yellowOffTime=250; //Declare yellowOffTime an int, and set to 250

int numYellowBlinks; //Number of times to blink yellow LED

int numRedBlinks; //Number of times to blink red LED

String redMessage="The Red LED is Blinking"; //Declaring a String Variable

String yellowMessage= "The Yellow LED is Blinking"; //Declaring a String Variable

void setup() {

Serial.begin(115200); // Turn on the Serial Port

pinMode(redLEDPin, OUTPUT); // Tell Arduino that redLEDPin is an output pin

pinMode(yellowLEDPin, OUTPUT); //Tell Arduino that yellowLEDPin is an output pin

Serial.println("How Many Times Do You Want the Red LED to Blink? "); //Prompt User for Input

while (Serial.available()==0){ } //Wait for User Input

numRedBlinks = Serial.parseInt(); //Read User Input

Serial.println("How Many Times Do You Want the Yellow LED to Blink? "); //Prompt User for Input

while (Serial.available()==0){ } //Wait for Input

numYellowBlinks = Serial.parseInt(); //Read User Input

}

void loop() {

Serial.println(redMessage);

for (int j=1; j<=numRedBlinks; j=j+1) { // Start our for loop

Serial.print(" You are on Blink #: ");

Serial.println(j);

digitalWrite(redLEDPin,HIGH); //Turn red LED on

delay(redOnTime); //Leave on for redOnTime

digitalWrite(redLEDPin,LOW); //Turn red LED off

delay(redOffTime); //Leave off for redOffTime

}

Serial.println(" ");

Serial.println(yellowMessage);

for (int j=1; j<=numYellowBlinks; j=j+1) { // Start our for loop

Serial.print(" You are on Blink #: ");

Serial.println(j);

digitalWrite(yellowLEDPin,HIGH); //Turn yellow LED on

delay(yellowOnTime); //Leave on for yellowOnTime

digitalWrite(yellowLEDPin,LOW); //Turn yellow LED off

delay(yellowOffTime); //Leave off for yellowOffTime

}

Serial.println(" ");

}

If you have been following these lessons, this code should make sense as we have built up step by step.

What we need to do now is to replace the four digitalWrite commands with analogWrite commands. Lets say that instead of applying 5 volts to the LED we want to apply 1 volt. This should make the LED’s blink noticeably dimmer. Remember that we would not analogWrite a value of 1, but need to calculate the write value from our formula. We want a voltage of 1 volt, so our write value should be 1 X 51, or the value 51. So now instead of digitalWrite, we should have a command like analogWrite(redLEDPin, 51) or analogWrite(yellowLEDPin, 51). Notice that on the commands that turn the LEDs off . . . digitalWrite(redLEDPin, LOW) would still work to turn the pins off, but I think it is good practice to change all the writes to analogWrites in a problem like this. To turn the pin off with an analog write would could use the command analogWrite(redLEDPin, 0).

With this new knowledge, you should modify your code and replace the 4 digitalWrite commands with analogWrite commands. Play around with writing different values to see the effect on the LED Brightness.

Technology Tutorials

Category Archives: Tutorial

LESSON 12: Simple and Easy Way to Read Strings, Int’s and float’s Over Arduino Serial Port

Lesson 11: Arduino Circuit to Dim LED with Potentiometer

LESSON 10: Analog Reads on the Arduino

LESSON 9: Ohm’s Law and Potentiometers

Lesson 8: Writing Analog Voltages in Arduino

Making The World a Better Place One High Tech Project at a Time. Enjoy!