Sense Hat Random Sparkles

sudo apt-get update
sudo apt-get upgrade

sudo apt-get install sense-hat

sudo apt-get install sense-hat

from sense_emu import SenseHat

from sense_hat import SenseHat

from sense_hat import SenseHat

sense = SenseHat()

Setting a single pixel on the Sense HAT

You can use the set_pixel command to control individual LEDs on the Sense HAT. To do this, you set the x and y  variables the set_pixel command takes. x indicates the HAT’s horizontal axis, and can have a value between 0 (on the left) and 7  (on the right). y indicates the HAT’s vertical axis, and can have a value between 0 (at the ltop) and 7 (at the bottom). Therefore, the x, y coordinates 0, 0 address the top left-hand LED, and the x, y coordinates 7, 7 address the bottom right-hand LED.

The grid above corresponds with the Raspberry Pi when it is this way around:

Let try out this example for setting a different colour in each corner of the Sense HAT’s LED matrix. You will need to use the set_pixel command multiple times in your code, like this:

from sense_hat import SenseHat
 
sense = SenseHat() # This clears any pixels left on the Sense HAT. You may not need this step and may want to choose when to add it in.
 
sense.clear()
sense.set_pixel(0, 0, 255, 0, 0)
sense.set_pixel(0, 7, 0, 255, 0)
sense.set_pixel(7, 0, 0, 0, 255)
sense.set_pixel(7, 7, 255, 0, 255)

Test setting the colour of different pixels using the Sense HAT Emulator:

The set_pixel method takes data in the following order:

x coordinate, y coordinate, red, green, blue

To define your set_pixel method, plug the names of your variables into the question marks in this line of code, in the right order: x coordinate, y coordinate, red, green, blue.

sense.set_pixel(?, ?, ?, ?, ?)

View the hint below if you are stuck.

I need a hint

Here is how your finished code should look — you will probably have chosen different numbers:

• Run your code by pressing F5. You should see a single LED light up on the Sense HAT’s LED display.

• Now change all of the numbers in your program and run the program again. A second LED should turn on.

Using the random module

So far you picked your own random numbers, but you can let the computer choose them instead by using the random module.

• Add another import line at the top of your program:

from random import randint

• Change your x  and y variables to be equal to a random number between 0 and 7. Now your program will automatically select a random position on the LED matrix.

Randomness in Python

One of the standard modules in Python is the random module. You can use it to create pseudo-random numbers in your code.

randint

You can generate random integers between two values using the randint function. For example, the following line of code will produce a random integer between 0 and 10 (inclusive).

from random import randint
num = randint(0,10)

uniform

If you want a random floating-point number (also called float), you can use the uniform function. For example, the following line of code will produce a random float that’s equal to or greater than 0, but less than 10.

from random import uniform
num = uniform(0,10)

choice

If you want to choose a random item from a list, you can use the choice function.

from random import choice
deck = ['Ace', 'King', 'Queen', 'Jack']
card = choice(deck)

• Run your program again, and you should see another random pixel being placed on the Sense HAT’s display. It will be the same colour you chose previously.

• Change your r,  g, and  b variables to each be equal to a random number between 0 and 255. Now your program will automatically select a random colour.

• Run the program again, and you should see another pixel appear in a random location, this time with a random colour.

• Run it a few more times, and you should see more of the grid fill up with random pixels.

If you have the sense.clear() line in your code, you will need to remove it. Otherwise, every time the program is re-run, the display will be cleared and your previous pixel will disappear.

Add a loop

Rather than running your program over and over by pressing F5, you can add a loop so that it will keep running by itself. 

• You can use the sleep module to pause the program between pixels. To do so, first add another import  to the top of your file.

from time import sleep

• Add an infinite loop on the line below the import statements.

While True loop in Python

The purpose of a while loop is to repeat code over and over while a condition is True.

This is why while loops are sometimes referred to as condition-controlled loops.

The example below is a while loop that will run forever - an infinite loop. The loop will run forever because the condition is always True.

while True:
    print("Hello world")

Note: The while line states the loop condition. The print line of code below it is slightly further to the right. This is called indentation - the line is indented to show that it is inside the loop. Any code inside the loop will be repeated.

An infinite loop is useful in situations where you want to perform the same actions over and over again, for example checking the value of a sensor. An infinite loop like this will continue to run forever meaning that any lines of code written after the loop will never happen. This is known as blocking - whereby a program blocks the execution of any other code.

• Indent all of the lines of code containing your variables and set_pixel so that they are within the loop:

I need a hint

• Add a line of code at the bottom of your program to pause for 0.1 seconds. Make sure that this line is indented level with the set_pixel line to show that it is inside the loop.

Using Python's sleep command

You can use the sleep function to temporarily pause your Python program.

• Add this line of code at the top of your program to import the sleep function.

from time import sleep

• Whenever you want a pause in your program, call the sleep function. The number in the brackets indicates how many seconds you would like the pause to be.

sleep(2)

You can pause for fractions of a second as well.

sleep(0.5)

• Run the code, and you should see random sparkles in action!

Challenge: better sparkles

• Can you make the sparkles change more quickly?

• Can you make the sparkles appear in pastel colours? (Hint: you normally pick colour variable values within the range of 0 to 255. Reduce the range and see what happens.)

• Try fixing one of the colour values to 0, and see what happens.

• Try making the sparkles disappear again in a style of your choosing.