Off logic with Pi and Picamera using GPIO

Question

Just trying to customize some Picamera functionality though this is my first time coding in Python. Basically I am using the GPIO with a button switch to essentially turn just the preview on and off. Ideally i did not want to use wait_for_edge because I wanted the pi to do other stuff in the interim and not be locked up waiting for the button press. Then I submitted to using it after the event detection I set up since its fine that the program waits while in preview mode (for this case).

The issue comes with just trying to use one button. I basically initiate event detection on the button, then remove it once preview mode starts. Then I set it up to wait for the button press again. But I run into:

RuntimeError: Conflicting edge detection already enabled for this GPIO channel

The following is meat of the code thus far:

from time import sleep
import picamera
import RPi.GPIO as GPIO
import datetime

today = datetime.datetime.today()
captureOn = 25


GPIO.setmode(GPIO.BCM)
GPIO.setup(captureOn, GPIO.IN, pull_up_down=GPIO.PUD_UP)
startPrev = True


def preview(channel):

        global captureOn
        global startPrev

        if GPIO.input(captureOn):
            print ("Rising Edge detected")
            sleep(.5)
        else:

            if (startPrev == True):

                with picamera.PiCamera() as camera:
                    camera.resolution = 1920, 1080
                    camera.framerate = 30
                    camera.rotation = 0
                    camera.brightness = 50
                    camera.start_preview()
                    while True:
                          sleep(1)
                          print('preview started')
                          startPrev = False
                          if GPIO.input(captureOn):
                                 break

            else:
                ...stop preview code?


                print('stop preview')




GPIO.add_event_detect(captureOn, GPIO.BOTH, callback=preview, bouncetime=1000)

EDIT: It seems that while in my IF statement, the GPIO event detection is disabled or not being called as pressing the button does nothing (no print outs either) FIXED: partially due to a wiring issue but added some code in the while statement above!

Answer 1

I highly suggest for practicality you eliminate the falling and rising reinstating altogether by using GPIO.BOTH as shown here. You would use GPIO.add_event_detect(25, GPIO.BOTH, callback=my_callback) and then check the input like so:

GPIO.setup(25, GPIO.IN) 
def my_callback(channel):
    if GPIO.input(25):     # if port 25 == 1
        print "Rising edge detected on 25"
    else:                  # if port 25 != 1
        print "Falling edge detected on 25"

# when a changing edge is detected on port 25, regardless of whatever 
# else is happening in the program, the function my_callback will be run
GPIO.add_event_detect(25, GPIO.BOTH, callback=my_callback)

Of course, you would replace the "print" lines with the turn on and off preview code. This link above contains a whole tutorial on the topic. Hope that helps!

EDIT: To print a different statement each time the button is pressed and switch between statement a and b use this code(its in c++ because I am more familiar with it, but you could convert it to Python quickly.):

bool printb = 0;

if(printb = 0)
{
  println(a);
  printb = 1;
}
else
{
 println(b);
 printb = 0;
}