[IDEA] Change GPIO state on mpd play / stop

[tristanc]

I've borrrowed / adapted a bash script I found on the internet to control a relay based on the contents of the /proc/asound/card0/pcm0p/sub0/status file.

It sits and checks that file every n seconds, and if 'RUNNING' is found, changes the state of y GPIO.

If 'RUNNING' is then not found it waits x seconds before changing the state of the y GPIO back again.

I run this as a service and it works well with mpd / shairport etc. However, it would be great to incorporate this in worker.php or somewhere more suitable.

The feature could be generalised - so if 'RUNNING' is found run 'up.sh' / not found run 'down.sh' - just like network configuration, as I'm sure there are other things people would like to run if they hit play.

The variables could be:

Check interval (seconds): n
State change delay (seconds): x
Set-up script (optional): allows initialisation of a specified GPIO pin on boot
Play script: user set field like the LCD update script
Stop script: user set field like the LCD update script

And in these two files the user could implement anything they want.

Or it could be made 'amplifier relay specific' as someone on the forum has done - with a dedicated page for amplifier control.

Code:

#!/bin/bash

set -e

#   Exports pin to userspace
echo "23" > /sys/class/gpio/export

# Sets pin 23 as an output
echo "out" > /sys/class/gpio/gpio23/direction

#time to wait until the amplifier is turned off in seconds
off_timer_time=60

#set variables
last_is_playing=0
off_timer=0

while true
do
    if cat /proc/asound/card0/pcm0p/sub0/status | grep -i RUNNING > /dev/null
    then
        is_playing=1
    else
        is_playing=0
    fi

    #0->1
    if [[ "$last_is_playing" -eq "0" && "$is_playing" -eq "1" ]]
    then
        off_timer=0
        echo "Turning amplifier on"
        echo "1" > /sys/class/gpio/gpio23/value
    fi

    #1->0
    if [[ "$last_is_playing" -eq "1" && "$is_playing" -eq "0" ]]
    then
        off_timer=1
    fi

    if [ "$off_timer" -ne "0" ]
    then
        if [ "$off_timer" -eq "$off_timer_time" ]
        then
            off_timer=0
            echo "Turning amplifier off"
            echo "0" > /sys/class/gpio/gpio23/value
        else
            ((off_timer++))
            #echo $off_timer
        fi
    fi

    last_is_playing=$is_playing
    sleep 1
done

Code:

[Unit]
Description=Automatic Amplifier Control

[Service]
Type=simple
ExecStart=/home/pi/autoamp.sh
User=root

[Install]
WantedBy=multi-user.target

#systemctl enable autoamp.service
#systemctl daemon-reload
#systemctl start autoamp.service