Auto LED Fader

In this program, you use two for loops to repeat the analogWrite() statement over and over again, giving an LED a smooth fade from dim to bright to dim.

Code

/* * Fade an LED's brightness up and down using 'for' loops and analogWrite() * The analogWrite() command works only on pins 3,5,6,9,10,11 */ void setup() { pinMode(5, OUTPUT); //LED } void loop() { //create a brightness var starting at 0 and increase it by 1 up to 255 for (int brightness = 0; brightness < 256; brightness++) { analogWrite(5, brightness); //each loop of the 'for' loop write the brightness value delay(5);//time between updating and writing the brightness variable } //create a new brightness variable starting at 255 decrease it by 1 to 0 for (int brightness = 255; brightness >= 0; brightness--) { analogWrite(5, brightness); delay(5); } } // (c) 2017 Let's Start Coding. License: www.letsstartcoding.com/bsdlicense

Challenges

How many can you complete? Change the code and hardware according to the challenges below. Upload your code to see the effect when you're finished. Complete a challenge? Check it off the list!

Add more LEDs on pins 3,6,9,10,11. Don't forget to use the pinMode() command to set them up.

Using the example code, copy and paste a new 'for' loop that will fade an LED up.
Create a new 'for' loop that fades an LED down.
Change the analogWrite() commands to use a new pin with an LED plugged into it.
Now your LEDs will toggle back and forth at the end of their fade.

Change each analogWrite() command to a digitalWrite() command. How does the outcome change?

Change each delay(5) to delay(2). Why is the difference so drastic?
Hint: The 'for' loop is running over 500 times for each full fade.

Videos

Read the Code Walkthrough Text (click to open)

In the void setup() function, you set your fading LED as an OUTPUT with pinMode(). Remember than analogWrite() (the function that will fade the LED) only works on pins 3,5,6,9,10,11 on the Mini Carrier board.

The void loop() contains only two for loops. The first for loop creates a brightness variable with a value of 0. As long as that variable is less than 256, the code between the curly braces of the for loop will run and brightness will be increased by one with the brightness++ command. Remember that brightness++ is the same thing as brightness = brightness + 1.

Inside the for loop, the analogWrite() function writes the value of the brightness variable to pin 5. During the first repetition of the for loop, the brightness is 0. During the second repetition of the for loop, the brightness is 1. By only delaying 5 milliseconds, the fade will look very smooth.

Once the first for loop has run 255 times, it is complete and the computer will look to the next line of code. In this program, it's another for loop.

This for loop creates a new variable called brightness. No matter where the last for loop ended, this for loop will start at 255. For example, if the last for loop ended with brightness of 10, this second for loop would still start with a brightness of 255. These variables have the same name, but they are not the same variable. You can change the name of brightness to any other name and the code will still run.

In the second for loop, the for loop will continue as long as brightness is greater than or equal to 0. Each time the for loop runs, it subtracts 1 from the value of the brightness variable. After this for loop has run 255 times, the brightness of the LED is back to 0.

Now the void loop() starts again, running the first for loop 255 times, then the second for loop 255 times.

This program matches up the names and values of the variables for a smooth look, but you could also mismatch the values of the variables so that the light fades up to half-brightness, then fades down from full brightness - it's all in the controls of the for loop.

Concepts

No new concept here- observe how the for loop can work with different components!

Quiz

If you're having trouble, try to run a program that can help you find the answer.

1. Which code commands can you use inside the curly braces of a 'for' loop?

Only analogWrite() and delay()
Only digitalWrite() and digitalRead()
Only tone() and noTone()
You can use any code commands inside a 'for' loop

2. True or False:
When you create a variable inside a 'for' loop, it only exists inside that 'for' loop.

True
False

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