Cygwin: May 2016

Saturday, May 7, 2016

How to turn LED dim and bright back again, using PWM On Raspberry Pi.

Code in Python:

Here I am using the Raspberry Pi Model B, connected to my Mac Laptop.
This was an experiment to try out using the PWM option available on the Raspberry.

The LEDs are connected to physical Pins 11

The white LED at one end is connected to Pin 11, ( i.e the GPIO17 ) , hence I'm using GPIO.BOARD in the python definition.

pi@raspberrypi~ $cat servo.py
import RPi.GPIO as GPIO # always needed with RPi.GPIO
from time import sleep # pull in the sleep function from time module

GPIO.setmode(GPIO.BOARD) # choose BCM or BOARD numbering schemes. I use BCM

GPIO.setup(11, GPIO.OUT)# set GPIO 11 as output for white led

white = GPIO.PWM(11, 100) # create object white for PWM on port 11 at 100 Hertz

white.start(0) # start white led on 0 percent duty cycle (off)

# now the fun starts, we'll vary the duty cycle to
# dim/brighten the leds, so one is bright while the other is dim

pause_time = 0.02 # you can change this to slow down/speed up

try:
while True:
for i in range(0,101): # 101 because it stops when it finishes 100
white.ChangeDutyCycle(i)
sleep(pause_time)
for i in range(100,-1,-1): # from 100 to zero in steps of -1
white.ChangeDutyCycle(i)
sleep(pause_time)

except KeyboardInterrupt:
white.stop() # stop the white PWM output
GPIO.cleanup() # clean up GPIO on CTRL+C exit