GPIO.wait_for_edge on 2 channels at once?

Question

So, I have 2 buttons set up on pins 17 and 27.

buttons = (17, 27)
GPIO.setup(buttons, GPIO.IN, pull_up_down=GPIO.PUD_UP)

I need to accept input from EITHER of these for a set period of time.

I found this code which works for 1 button here

channel = GPIO.wait_for_edge(17, GPIO_RISING, timeout=5000)
if channel is None:
    print('Timeout occurred')
else:
    print('Edge detected on channel', channel)

I changed "GPIO_RISING" to "GPIO.RISING" to get it to work.

As mentioned this works fine for 1 button, and can detect the button press. The problem is when I try and alter the code to accept the second button.

channel = GPIO.wait_for_edge(17, GPIO.RISING, timeout=5000)
channel1 = GPIO.wait_for_edge(27, GPIO.RISING, timeout=5000)

if channel is None and channel1 is None :
    print('Timeout occurred')
elif channel is not None:
    print('Edge detected on channel', channel)
elif channel1 is not None:
    print('Edge detected on channel', channel1)
else:
    print('something')

This makes channel detectable for the first 5 seconds and channel1 detectable the next 5 seconds, not concurrently.

How do I solve this?

Answer 1

The answer of joan is probably working fine, but with the event_detected() function you can also do it like this:

GPIO.add_event_detect(17, GPIO.RISING)  # add rising edge detection on a channel
GPIO.add_event_detect(27, GPIO.RISING)  #for both buttons

start = time.time()
while True:
    if GPIO.event_detected(17):
        print('Button 1 pressed')
    if GPIO.event_detected(27):
        print('Button 2 pressed')
    if time.time() - start > 5:
        print('Timeout')
    time.sleep(0.0001)

See documentation for more info.

Answer 2

You will need to use callbacks, to detect both signals. Use a queue, to communicate with the main program:

from queue import Queue, Empty

queue = Queue()
GPIO.add_event_detect(17, GPIO.RISING, queue.put)
GPIO.add_event_detect(27, GPIO.RISING, queue.put)

# wait for a event for 5 seconds
try:
    event = queue.get(timeout=5)
except Empty:
    event = None

GPIO.remove_event_detect(17)
GPIO.remove_event_detect(27)

if event is None:
    print("timeout")
else:
    print("event on {}".format(event))

Answer 3

You will need to adopt a different design.

wait_for_edge "does what it says on the tin". It waits for an edge or times out.

I'd use a GPIO callback (add_event_detect in RPi.GPIO terms) and have a different callback triggered by each GPIO.

Something like (pseudo code to give an idea)

def callback_1():
   global GPIO1_triggered
   set GPIO1_triggered

def callback_2():
   global GPIO2_triggered
   set GPIO2_triggered

GPIO1_triggered = False
GPIO2_triggered = False

add_event_detect(GPIO1, callback1)
add_event_detect(GPIO2, callback2)

stop = time.time() + 5

while not GPIO1_triggered and not GPIO_2 triggered and time.time() < stop:
   time.sleep(0.01)

cancel_event_detect(GPIO1)
cancel_event_detect(GPIO2)

if GPIO1_triggered:
   code
elif GPIO2_triggered:
   code
else:
   code