Start Arduino course 02 - Fade
Introduction:
You know how to turn an LED on and off with the Arduino, the next skill to
master is how to control the brightness. To do this you are going to start
reading switch values. After you have learnt to fade an LED automatically, you
will use a button to create a random brightness, and then go on to use a
potentiometer to control the brightness.
Goals
•
•
•
•
Make an LED fade up and down automatically.
Use a button to turn an LED on and off.
Make an LED have a random brightness at the push of a button.
Control the brightness of an LED with a potentiometer.
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Pulse Width Modulation (PWM)
Look at the Arduino Digital pins closely, you will notice that 6 of the pins have
tilda signs (~) next to the pin number.
These are to tell us that this pin can perform Pulse Width Modulation (PWM), a technique in
digital computing used to create the perception of changeable voltage. Digital pins can only
output 0v or 5v (On or Off). With PWM it creates the illusion that we are outputting different
voltages to this. This is managed by switching the state of our Arduino pin from high to low
very quickly, much like what happened when we changed the delay of our blink sketch to 10
milliseconds. Another way we can do this is to use the Arduino’s analogWrite() function.
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Circuit 2.0 - Fade
Hardware
This code and circuit will fade an LED on and off using the analogWrite
function.
For this, we will need:
1x Arduino Uno
1x USB cable
1x Breadboard
1x LED
1x 220 Ohm Resistor
(Red Red Brown Gold)
2x Jumper wires
You will notice there are a lot of similarities between this circuit and the blink circuit, The two
main differences are we have moved our jumper from pin 13 to pin 11. This is because pin 13 is
not able to use the analogWrite() function (no tilda sign).
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Circuit 2.0 - Fade
Code
Make a new sketch in the Arduino IDE
Copy the code below.
and name this ‘Fade’.
/*
Fade
This example shows how to fade an LED on pin 11
using the analogWrite() function.
This example code is in the public domain.
*/
int led = 11;
int brightness = 0;
int fadeAmount = 5;
// the pin that the LED is attached to
// how bright the LED is
// how many points to fade the LED by
// the setup routine runs once when you press reset:
void setup() {
// declare pin 11 to be an output:
pinMode(led, OUTPUT);
}
// the loop routine runs over and over
void loop() {
// set the brightness of pin 11:
analogWrite(led, brightness);
// change the brightness for next time through the loop:
brightness = brightness + fadeAmount;
}
// reverse the
if (brightness
fadeAmount =
}
// wait for 30
delay(30);
direction of the fading at the ends of the fade:
== 0 || brightness == 255) {
-fadeAmount ;
milliseconds to see the dimming effect
Once you have copied the code, press
(upload) and watch the results!
(compile) and if no errors appear, press
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Start Arduino course 02 - Fade
My code won’t compile!
Is your computer asking you to choose
the right Serial port?
- Check your spelling.
Is everything spelt correctly?
- Check your punctuation.
Are all your lines ending in a semi-colon?
Do you have the correct capital letters?
This can be solved by going to:
Tools > Port > dev/tty.usb.... for Mac
Tools > Port > COM... for Windows.
- Did you close the curly brackets?
Make sure your void setup and void loop
both have everything surrounded by the
open and closed curly brackets.
Let’s go through the code understand what every part is doing.
Global Variables
These are always initialized outside both void setup
and void loop functions, so they are accessible in both.
int led = 11;
int brightness = 0;
int fadeAmount = 5;
void setup()
void setup() {
// declare pin 11 to be
an output:
pinMode(led, OUTPUT);
}
This function, which is only used once at the start of
the program. This is where we set our Led pin to be an
output using pinmode(). Take note of the open curly
bracket to start the loop and closing bracket to show
when the loop ends.
void loop()
void loop()
Everything within the curly brackets of the void loop is
constantly looped over while the program is running.
{
analogWrite()
analogWrite(led, brightness);
This is how we create our PWM, the first variable is
which digital pin this will be, the second is how much it
is going to be. This value has to be between 0 and 255.
In our case, we are using our variable names, and this
is going to change the brightness of the Led (11) using
the brightness variable.
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Start Arduino course 02 - Fade
Brightness
This line is how we increase the brightness of LED.
Every time void loop is calls this, the value of
fadeAmount is added to brightness. In this instance,
brightness adds 5, as this is the value we stated
fadeAmount is.
brightness = brightness +
fadeAmount;
if statement
This is the part of our program that makes sure the
brightness of our LED constantly loops. This is called
an ‘if statement’. These, like void loop and void setup,
use the curly brackets to signal what needs to be done
inside this statement, with everything inside the
normal brackets the check statement. In our program,
every time we reach the if statement in our code, the
program checks integer brightness and if its value is
either 0 or 255. If this brightness has a value of one of
these, it simply inverts the value of fadeAmount. This
means that if brightness has the value of 255, it will add
-5 to the amount, making the brightness of the LED
decrease. If the value of brightness is 0, it will add 5 to
the brightness, making the LED brighter.
if (brightness == 0 ||
brightness == 255) {
fadeAmount = -fadeAmount ;
}
delay()
This adds a pause to our loop. In this instance, the
delay is 30 milliseconds. We do this to slow the
dimming of the LED.
delay(30);
Once we are happy our code works and is uploaded to our Arduino, we can save this program
to our computer using the save button
, Naming it ‘Fade’.
Circuit 2.0 - Fade
Challenge
- Can you make the LED fade faster?
- Can you fade the LED on a different digital pin?
- What is the highest and lowest value you can use with analogWrite() ?
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Start Arduino course 02 - Fade
Buttons
Now we have our fading LED, let’s control this with an input. For this, we’re
going to use one of our pushbuttons.
Pushbuttons (also known as
tactile switches), are what we
use to open and close circuits.
Buttons and switches are used
in electronics to allow us to
interact with our circuits.
We’re going to use one with
fading LED to change the
outcome.
You are now going to try two
ways to use the pushbutton to
change a circuit:
2.1 - In a simple series circuit
to open and close the circuit
directly.
2.2 - Isolate the button from
the circuit and use the arduino
to process the information.
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Circuit 2.1 - Fade (Push Button/series) Hardware
We will use the push button in series with our led to open the circuit. This
means the flow of electricity is stopped as there is an incomplete circuit
flowing from the positive (digital pin) to negative (ground).
For this, we will need:
1x Arduino Uno
1x USB cable
1x Breadboard
1x LED
1x Push button
1x 220 Ohm resistor
(Red, Red, Brown, Gold)
3x Jumper Wires
Circuit 2.1 - Fade (Push Button/series) Challenge
- What happens when the pushbutton is pressed?
- Why does this happen?
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Start Arduino course 02 - Fade
Circuit 2.2 - Fade (Digital Read + LED)
Hardware
The second method is to use the pushbutton isolated with a digital pin and
program the arduino to change the outcome.
For this, we will need:
1x Arduino Uno
1x USB cable
1x Breadboard
1x LED
1x Push button
1x 220 Ohm resistor
(Red, Red, Brown, Gold)
1x 10k Ohm resistor
(Brown Black Orange Gold)
8x Jumper Wires
The resistor used with the button is known as a pull down resistor. This ensures that when the
button is open, the circuit is still completed through the resistor and creates a solid connection
to voltage or ground.
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Circuit 2.2 - Fade (Digital Read + LED)
Make a new sketch in the Arduino IDE
Read+LED’.
Copy the code below.
Code
and name this ‘Fade_digital
/*Digital Read & LED
This code is for using a Push Button to change the state of an LED
*/
int led = 11;
int pushButton = 7;
void setup(){
//set pinMode of LED pin (11)
pinMode(led, OUTPUT);
//set pinMode of pushButton pin (7)
pinMode(pushButton, INPUT);
}
void loop() {
//if statement to check the state of button
if (digitalRead(pushButton) == HIGH) {
//LED on
digitalWrite(led, HIGH);
}
}
if(digitalRead(pushButton) == LOW){
//LED off
digitalWrite(led, LOW);
}
Once you have copied the code, press
(upload) and watch the results!
(compile) and if no errors appear, press
Page 10 - Start Arduino Course: 02 Fade
Start Arduino course 02 - Fade
Let’s go through the code understand what every part is doing.
Global Variables
These are defined outside both void setup and void
loop as they can be used in both. We have set two
integers led and pushButton to the values 11 and 7.
These are the numbers of the digital pins we are using
with them.
int led = 11;
int pushButton = 7;
void setup()
void setup(){
//set pinMode of led pin
(11)
pinMode(led, OUTPUT);
//set pinMode of
pushbutton pin (7)
pinMode(pushButton,
INPUT);
}
This is only called once at the start of the program. In
here we set the states of the LED and Push Button pins.
As we are using the LED pin to light up the LED, this is
an OUTPUT pin. As we are sensing the push button pin,
this is an INPUT pin.
void loop()
void loop()
This is the start of our void loop function, we use the
curly brackets to signal the start and end of the
function. Everything within these curly brackets is
looped infinitely while the program is running.
{
if statements
//if statement to check
the state of button
if (digitalRead
(pushButton) == HIGH) {
//led on
digitalWrite
(led, HIGH);
if(digitalRead(pushButton) == LOW){
//led off
digitalWrite(led,
LOW);
}
This is one of two if statements we have used in this
program. An if statement is a way of defining an
outcome dependent on an input. In this instance, we
have used Arduino function digitalRead() to check the
push button pin state. As it is a Digital pin, it has two
states – High or Low. This if statement checks for the
input being HIGH. If this is true, the state of the LED pin
is set to HIGH using digitalWrite(). If not, the program
moves onto the next line.
This if statement effectively looks for the opposite
of the one above, checking to see if the push button
hasn’t been pressed. The outcome of that is that the
LED pin state is LOW using digitalWrite().
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Circuit 2.3 - Digital Read (Fade + Button) Hardware
Now we have learnt about LED Fade and Push buttons, let’s bring them
together. You are going to write a new sketch to create a random brightness
for the LED at the push of the button.
For this, we will need:
1x Arduino Uno
1x USB cable
1x Breadboard
1x LED
1x Push button
1x 220 Ohm resistor
(Red Red Brown Gold)
1x 10k Ohm resistor
(Brown Black Orange Gold)
8x Jumper Wires
The circuit is going to stay the same as before. (Circuit 2.2 - Fade (Digital Read + LED))
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Circuit 2.3 - Digital Read (Fade + Button) Software
Make a new sketch in the Arduino IDE
fade+button’. Copy the code below.
and name this ‘DigitalRead_
/*Digital Read & LED
This code is for using a PushButton to change the state of an LED
*/
int led = 11;
int pushButton = 7;
int randomNum = 0;
void setup(){
//set pinMode of led pin (11)
pinMode(led, OUTPUT);
//set pinMode of pushbutton pin (7)
pinMode(pushButton, INPUT);
}
// the loop routine runs over and over again forever;
void loop() {
//if statement to check the state of button
if (digitalRead(pushButton) == HIGH) {
//led on
analogWrite(led, randomNum);
}
}
if(digitalRead(pushButton) == LOW){
//led off
randomNum = random(0, 255);
}
Once you have copied the code, press
(upload) and watch the results!
(compile) and if no errors appear, press
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Start Arduino course 02 - Fade
My code won’t compile!
Is your computer asking you to choose
the right Serial port?
- Check your spelling.
Is everything spelt correctly?
- Check your punctuation.
Are all your lines ending in a semi-colon?
Do you have the correct capital letters?
This can be solved by going to:
Tools > Port > dev/tty.usb.... for Mac
Tools > Port > COM... for Windows.
- Did you close the curly brackets?
Make sure your void setup and void loop
both have everything surrounded by the
open and closed curly brackets.
Let’s go through the code understand what every part is doing.
There are many similarities between this and the previous program. The main difference is the
inclusion of random().
Random()
is an Arduino function used to create a random number
between two values (0 and 255 in this instance).
randomNum = random(0,
255);
The outcome of this program is that every time the
push button is pressed, the program generates a new
random brightness for the LED, displaying it constantly
when the push button is not pressed. It does this by
using the digitalRead() argument to distinguish if the
push button pin is pressed. If the push button is not
pressed, a random value is generated. When push
button is pressed, this value is used as the brightness
for analogWrite().
Circuit 2.3 - Digital Read (Fade + Button) Challenge
- Can you make the LED always LOW when the push button is not pressed?
- Could you do this with TWO LEDs?
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Circuit 2.4 - Potentiometer + LED Hardware
Now we have controlled our Led with a button, let’s try and use a
potentiometer.
A potentiometer is a resistor that allows the user to change the potential of the resistance by
turning the knob. Potentiometers have three legs, the three legs are: input, output and ground.
As we are simply using the data as a sensor value, and not using it to change the resistance of
an outcome, our input will be 5v. This means our value range will fit perfectly to the analog In
range of 0 – 5v.
For this, we will need:
1x Arduino Uno
1x USB cable
1x Breadboard
1x LED
1x Potentiometer
1x 220 Ohm resistor
(Red Red Brown Gold)
7x Jumper Wires
The circuit is basically made up of two different mini circuits - the potentiometer and the LED.
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Circuit 2.4 - Potentiometer + LED Hardware
Software
Make a new sketch in the Arduino IDE
LED’. Copy the code below.
and name this ‘Potentiometer_
//variables set with pins of potentiometer and LED
int pot_pin = 0;
int led_pin = 11;
//variable for storing potentiometer value
int pot_value = 0;
void setup() {
//put your setup code here, to run once:
}
//set LED pin to output mode
pinMode(led_pin, OUTPUT);
void loop() {
//put your main code here, to run repeatedly:
//sample potentiometer pin and store value in pot_value
pot_value = analogRead(pot_pin);
//use pot value to change brightness of LED
analogWrite(led_pin, pot_value / 4);
}
//pause loop for 50 milliseconds so readings happen every 50ms
delay(50);
Once you have copied the code, press
(upload) and watch the results!
(compile) and if no errors appear, press
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Start Arduino course 02 - Fade
My code won’t compile!
Is your computer asking you to choose
the right Serial port?
- Check your spelling.
Is everything spelt correctly?
- Check your punctuation.
Are all your lines ending in a semi-colon?
Do you have the correct capital letters?
This can be solved by going to:
Tools > Port > dev/tty.usb.... for Mac
Tools > Port > COM... for Windows.
- Did you close the curly brackets?
Make sure your void setup and void loop
both have everything surrounded by the
open and closed curly brackets.
How does it work?
Global Variables
These are the global variables created to store the pin
numbers of both our digital LED and analog
potentiometer.
int pot_pin = 0;
int led_pin = 11;
Global Variables
This is the variable for storing our analog
potentiometer data. The range will be between 0 and
1023.
int pot_value = 0;
void setup()
void setup()
The void setup() is where we initialise our program, as
everything within the curly brackets is called once.
{
pinMode
pinMode(led_pin, OUTPUT);
We initialise our digital LED pin to be an output pin in
the void setup(), as it only needs to be initialised once.
void loop()
void loop()
{
The void loop() function is where the main looping
of our program happens. Everything within the curly
brackets of void loop will be repeated one line after the
other and back to the top continuously while the
program is running.
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analogRead()
analogRead() is an Arduino function used to sample
analog In pins. The desired analog pin number is set
within the normal brackets (in our case, pot_pin, which
is 0). This value is then stored in the integer pot_value.
pot_value =
analogRead(pot_pin);
analogWrite()
analogWrite(led_pin, pot_
value / 4);
The value stored is then used in another Arduino
function analogWrite(). This is how we use the
technique PWM to fade our LED. The potentiometers
analog value is divided by 4 as this brings it down to fit
within scale of analogWrite() (0 – 255).
delay()
delay(50);
We add a delay to pause the program loop, meaning
the sampling our data only happens every 50
milliseconds.
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