2.1: LED

Goals: By the end of this lesson, I will be able to:

1. Explain how an LED functions
2. Describe how LEDs can be used to communicate
3. Explain how RGB color values can be used to create primary colors
4. Explain how to make a wide variety of colors by blending RGB values
5. Use the LED to communicate information about a program while it runs
6. Explain how the sleep function can be used to change the duration of LED on and off sequences

Steps to Success:

1. 1. What is an LED?
   2. set_drone_LED
   3. Need to Take a Break? Let’s Sleep On It!
   4. Program a Solid LED
   5. Challenge 1: Color Bar
   6. Challenge 2: Menu With Lights

LED stands for “light-emitting diode”. A diode is an electronic device that allows an electronic current to flow in only one direction. LEDs are everywhere and can be any color. LEDs range from small components that can be used for building circuits or as big and bright as stadium lights. LEDs have replaced traditional incandescent light bulbs because they are more efficient. 

CoDrone EDU has 1 RGB LED on the main body. There are also 4 RGB LEDs in your CoDrone EDU controller. RGB stands for red, green, and blue. An RGB LED is actually made up of three individual LEDs for red, green, and blue. Using the three colors, you can create almost every color imaginable! Aside from making your drone look cool, LEDs provide another form of feedback. 

The most basic LED function that you can use is set_drone_LED. This function allows you to change the color of the LED built into the drone. The set_drone_LED function has four inputs: r, g, b, and brightness. For the r, g, and b values, these combination of these values determine what color is displayed on the drone and can range from 0 to 255. The brightness value determines how bright the drone LED will be and can also accept any value from 0 to 255.

The other LED function that you can use to change an LED’s color is set_controller_LED. Like the set_drone_LED function, set_controller_LED has the same four inputs: r, g, b, and brightness. Using the function will allow you to change the color of the LEDs on your controller separately from the drone!

Before we get started with the LED, we need to understand the sleep(seconds) function. This is part of the time  library which needs to be imported, just like we import the codrone_edu library. The sleep function takes in an integer or decimal value that represents the number of seconds you want the program to pause before it moves on to the next step. This is helpful to make sure the drone completes a movement, sequence, or procedure before moving on to the next step. It also allows us to see the results of the LED’s color change before it moves on to the next. check out the example code below that uses the sleep function:

from codrone_edu.drone import *
import time

drone = Drone()
drone.pair()

drone.takeoff()
time.sleep(3)
drone.land()

drone.close()

Now that we know the purpose of the sleep function, let’s make a program that changes the drone and controller’s LED color from red to green and then finally to blue:

from codrone_edu.drone import *
import time

drone = Drone()
drone.pair()

drone.set_drone_LED(255, 0, 0, 100)   # Red
drone.set_controller_LED(255, 0, 0, 100)  # Red

time.sleep(1) 

drone.set_drone_LED(0, 255, 0, 100) # Green
drone.set_controller_LED(0, 255, 0, 100) # Green

time.sleep(1)

drone.set_drone_LED(0, 0, 255, 100) # Blue
drone.set_controller_LED(0, 0, 255, 100). # Blue

time.sleep(1)

Once you have this program working, try playing with the sleep time and see what happens. You can even try decimal values!

You can also turn off the LEDs on both the drone and controller.

• drone_LED_off()
• controller_LED_off() 

Try flashing your LED on and off with some delays in between.

Now that we know the basics of using the LED, let’s add it to a flight program! For this challenge, you will create a program that has the drone fly to 3 different altitudes. At each Altitude, have the drone change its light to a color of your choosing. Make sure that, for this challenge, you complete the following requirements:

1. Have the drone takeoff then fly to 3 different altitudes
2. Use 3 different colors (one at each altitude)
3. Pause for at least 3 seconds between each altitude level to give your lights time to play
4. Land  the drone once completed

One other important note:

If you decide to use an LED function before takeoff, make sure you sleep for at least 1 second before the takeoff command, otherwise, the program may miss LED command and it may not get displayed. See the code below for an example:

drone.set_drone_LED(255, 0, 0, 100) 
time.sleep(1)       # Add a time.sleep(1) before takeoff
drone.takeoff()

For your second challenge, we will make our own Red Light, Green Light game with our drone! This game will require you to manually fly your drone with your controller while your LEDs will change color at random intervals. Choose a take off zone and a finish line. Try to fly your drone across the finish line but you are only allowed to move when your LEDs are green. If you move when the LEDs are red start from the beginning! Your program should have the following

1. Use the randint function to randomly choose a color and time. If you need a refresher look back at the while loop lesson!
2. The only flight command in your program should be a take off
3. Once your drone is in the air, press the power button once to switch from the link state to manual flying state
4. Your drone and controller will continue to change color while in manual flying state.
5. Play the Red Light, Green Light game!

Here is one example of how this could be programmed. Have fun!

from codrone_edu.drone import *
import time
from random import randint
drone = Drone()
drone.pair()

drone.takeoff()

while True:
    random_color = randint(1, 2)
    random_delay = randint(1, 4)

    if random_color == 1:
        drone.set_drone_LED(255, 0, 0, 100)
        drone.set_controller_LED(255, 0, 0, 100)

    else:
        drone.set_drone_LED(0, 255, 0, 100)
        drone.set_controller_LED(0, 255, 0, 100)

    time.sleep(random_delay)

In this lesson, you learned about LEDs, including how they work, what they are used for, and how to program the LEDs on your CoDrone EDU. You also learned about RGB values and how to create various colors by blending different RGB values.