The gist of the script is that it checks the GPIO pin every half second and shuts the system down if the pin goes low. I use an external pullup resistor as I did not want to have to install the wiring library (not that I have a problem with it at all).
The hardware used is a 10k pullup resistor to 3v3 on the header. The other end is connected to GPIO0 (one pin lower). A momentary switch is connected from the GPIO pin to ground. The diagram for the P1 headder and a diagram of how to make the circuit is provided in the wiki.
Here is the script:
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# This script is used to check a pin at half second intervals and
# will shutdown the system if the pin is at a low level.
# Portions of this script adapted from "GPIO Driving Example (Shell script)"
# found on elinux.org .
# Note that the GPIO numbers that you program here refer to the pins
# of the BCM2835 and *not* the numbers on the pin header.
# So, if you want to activate GPIO7 on the header you should be
# using GPIO4 in this script. Likewise if you want to activate GPIO0
# on the header you should be using GPIO17 here.
# GPIO numbers should be from this list
# 0, 1, 4, 7, 8, 9, 10, 11, 14, 15, 17, 18, 21, 22, 23, 24, 25
## I'm not sure what all that means but using a 0 in this script
## indicates using the pin just next to 3v3 (the not 5v one)
# use GPIO 0 as indicated on the header
# this pin will be used to shutdown the system
# Set up GPIO 17 and set to input
echo "$PIN_ON_BCM2835" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio"$PIN_ON_BCM2835"/direction
# if the pin exists ...
# if the pin is low do the shutdown command with halt now.
# That is in 0 seconds.
while ( true ); do
if [ -a "$READ_PIN_PATH" ]; then
if [ $(<$READ_PIN_PATH) == 0 ]; then
shutdown -h 0
echo "pin is low"
# a small delay
# for debugging just show the pin value
# echo $(<$READ_PIN_PATH)
in the script that launches this script I have:
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if [ -e "$READ_PIN_PATH" ]; then
echo reset already being checked
sudo /home/pi/watch_reset.sh &
one question I have is where to put the second script... I hate to say where I have it now... should it go in /etc/init.d/ ??
I really don't know how that stuff works. Is there a better place to put a script like this... such as in chron @reboot ??