Hello World - Raspberry Pi Mechatronics Projects - page 17

3. We will import the sleep class from the time module in the first line. This is

required to introduce a 1-second delay between turning the LED on and off every
other second:
from time import sleep

4. We also need the pin class from the quick2wire GPIO library:
from quick2wire.gpio import Pin

5. We need to set the output pin that we will be using in the example:

LED_output = Pin(8, Pin.Out)

6. We can set the pin to the logical high (3.3 V) as follows:
LED_output=1

7. We will set the pin to the logical low (0 V) as follows:
LED_output=0

8. We will execute the same thing using an infinite while loop:
while True:
LED_output=1
sleep(1)
LED_output=0
sleep(1)

9. This will make the LED blink with a 1-second delay. We should also note the indent
on the blink sequence. The blink sequence has a different indent compared to the
while loop. Hence, the code that is at a different indent is executed infinitely.
10. When the program is interrupted (by pressing CTRL + C on the keyboard), we need
to unexport the pins at exit:
out_pin.unexport()

An alternative to quick2wire - RPi.GPIO
1. Another alternaive is to use RPi.GPIO ( https://pypi.python.org/pypi/RPi.
GPIO ) . It comes as a standard package along with the Raspbian Wheezy OS. Let's
perform a quick review of the code:
import RPi.GPIO as GPIO
from time import sleep

GPIO.setmode(GPIO.BCM)
GPIO.setup(8,GPIO.OUT)