In Chapter 3, Blinking External LEDs we did a dancing LEDs exercise. We created an illusion light is traveling from one end to the other and from the other end back. Let's write a Python program to achieve the same. Connect seven LEDs with resistors as shown in Chapter 3. Type the following program in Cloud9, save it as dance_LEDs.py and run. You should be able to see light travelling to and fro from both ends.
This is the code for dance_LEDs.py:
#!/usr/bin/python
import Adafruit_BBIO.GPIO as GPIO
from time import sleep
LED_pins = ["P8_7","P8_9","P8_11","P8_13","P8_15","P8_17","P8_19"]
for led in LED_pins:
GPIO.setup(led,GPIO.OUT)
while True:
for led in LED_pins:
GPIO.output(led,GPIO.HIGH)
sleep(0.1)
GPIO.output(led,GPIO.LOW)
for led in reversed(LED_pins):
GPIO.output(led,GPIO.HIGH)
sleep(0.1)
GPIO.output(led,GPIO.LOW)In this program, we have created a list of strings with the name LED_pins. This list has the name of all the GPIO pins that has actual LEDs connected to.
- First, we iterated through this list and set the direction of all the pins as output.
- Then we ran a
whileloop for ever. Inside thewhileloop, we used aforloop to iterate through the listLED_pins. Inside this loop, we turned each pinHIGHfor 1 millisecond one by one. So, the actual LEDs glow one by one up to the other end. - After that, in another
forloop, we did the same onreversedlist ofLED_pins. Python has the functionreversed(), which reverses elements in a list. Here, we get actual LEDs glowing one by one in a reverse direction.
The above sequence runs until we stop the program manually. If you get any errors, please check the troubleshooting steps in Chapter 3, Blinking External LEDs.