GPIO Listening to Buttons!

First order of business is to import some libraries to help send/receive signals to/from the GPIO pins of the Raspberry Pi.



In [1]:

    
import RPi.GPIO as GPIO
import time

The following code will set the mode to a Broadcom pin layout (which seems to be what we want). We'll also go ahead and set up the LED output pin.



In [2]:

    
GPIO.setmode(GPIO.BCM)
outpin = 25
GPIO.setup(outpin, GPIO.OUT)

Buttons

Buttons require us to 'listen' indefinitely for input to our GPIO pin. We use an infinite loop to do this. To stop the loop, you simply click Kernel/Interrupt in the menu above.

Once the button is wired to the pin designated below (inpin #) with the appropriate resistors, set up the port as an input port:



In [3]:

    
inpin = 18
GPIO.setup(inpin, GPIO.IN, pull_up_down=GPIO.PUD_UP) # the pull_up_down keeps us from worrying about pull-up resistors



In [4]:

    
prev_input = 1 # looking for a 'False' as the button press signal, so we start with a "True"
while True:
    #take a reading
    input = GPIO.input(inpin)
    #if the last reading was low and this one high, print
    if ((not prev_input) and input):
        print("Button pressed")
    #update previous input
    prev_input = input
    #slight pause to debounce
    time.sleep(0.05)









    



Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Button pressed






    



---------------------------------------------------------------------------
KeyboardInterrupt                         Traceback (most recent call last)
<ipython-input-4-aaa1358d86dd> in <module>()
      9     prev_input = input
     10     #slight pause to debounce
---> 11     time.sleep(0.05)

KeyboardInterrupt:

So, now let's do something with that button press -- how about flashing our light, then taking a photo.

We'll first import the camera class...



In [5]:

    
from picamera import PiCamera, Color
from time import sleep

We'll wait to instantiate our camera object, just so we don't crash anything with a bunch of button presses.



In [8]:

    
def blink_and_shoot(idx):
    """ idx: an index number for photos to be stored at /img/snapshot-[idx] """
    
    # set up camera
    with PiCamera() as camera:
        #camera.resolution = (480, 320)  # uncomment this line if you want smaller photos
        camera.vflip = True
        camera.hflip = True
        camera.start_preview()

        for i in range(3):
            GPIO.output(outpin, True)
            time.sleep(0.2)
            GPIO.output(outpin, False)

        #camera.image_effect = 'oilpaint' # just to make things interesting
        sleep(0.5)
        camera.capture('img/snapshot-%s.jpg' % idx)
        camera.stop_preview()

Now for the infinite button loop to listen for a press:



In [9]:

    
prev_input = 1 # looking for a 'False' as the button press signal, so we start with a "True"
counter = 1
while True:
    #take a reading
    input = GPIO.input(inpin)
    #if the last reading was low and this one high, print
    if ((not prev_input) and input):
        print("Taking photo%s" % counter)
        blink_and_shoot(counter)
        counter += 1
    #update previous input
    prev_input = input
    #slight pause to debounce
    time.sleep(0.05)









    



Taking photo1






    



---------------------------------------------------------------------------
KeyboardInterrupt                         Traceback (most recent call last)
<ipython-input-9-4894fa54a842> in <module>()
     12     prev_input = input
     13     #slight pause to debounce
---> 14     time.sleep(0.05)

KeyboardInterrupt:



In [10]:

    
GPIO.cleanup()



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