Non-latching GPIO output that needs to disregard input - gpio

Question

New to programming, so I'll try my best to explain:
I'm trying to use a Pi Zero in my solar setup to switch the power-on input on an x86 motherboard (basically operating as the power button). The idea is that a battery voltage monitor sets pin 14 on the Pi high when the battery is at a high enough voltage. The script reads this input then switches an output (26) on the Pi, which in turn closes a relay for one second, which will then activate the power-on input on the motherboard.
The problem is that I cannot get the output (26) to turn off after one second. The script won't ignore pin 14, and just keeps the output (26) high. (Pin 14 is naturally held high by the battery monitor until the battery level falls down below a certain threshold)
import RPi.GPIO as GPIO
from time import sleep
GPIO.setmode(GPIO.BCM)
GPIO.setup(14,GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(26,GPIO.OUT)
GPIO.output(26, 1)
while True:
if GPIO.input(14)==1:
GPIO.output(26, 0)
sleep(1)
GPIO.output(26, 1)
else:
GPIO.output(26, 1)
GPIO.cleanup()

Answer 1

Here's one possible solution that polls the value of GPIO14 1/second
and uses the variable power_on to figure out how we respond to the
value:
import RPi.GPIO as GPIO
from time import sleep
GPIO.setmode(GPIO.BCM)
GPIO.setup(14,GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(26,GPIO.OUT)
GPIO.output(26, 1)
power_on = False
while True:
if not power_on:
if GPIO.input(14) == 1:
GPIO.output(26, 0)
sleep(1)
GPIO.output(26, 1)
power_on = True
else:
if GPIO.input(14) == 0:
power_off = True
time.sleep(1)
# Note that you're never going to reach this line.
GPIO.cleanup()
Alternatively, you can have your code block until pin 14 changes, leading to something like this:
import RPi.GPIO as GPIO
from time import sleep
GPIO.setmode(GPIO.BCM)
GPIO.setup(14,GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(26,GPIO.OUT)
GPIO.output(26, 1)
while True:
GPIO.wait_for_edge(14, GPIO.RISING)
GPIO.output(26, 0)
sleep(1)
GPIO.output(26, 1)
# Note that you're never going to reach this line.
GPIO.cleanup()
This uses GPIO.wait_for_edge() to wait for a rising edge on GPIO14 (a low ➡️ high transition), and then triggers your relay.