Auto Amp On / Off

Trevor Cockayne

May 28, 2016 14:24

None

A Crude Script I am using to automatically turn my amp on and off

#!/bin/bash

# This Script is to read the Alsa Sound State and Automatcally
# swing a GPIO pin to allow auto switch on / off of an external
# amplifier, its crude dirty and badly written any sugestions
# or criticism welcome
#
# Trevor Cockayne trevoml@gmail.com

# Exports pin to userspace
echo "26" > /sys/class/gpio/export

# Sets pin 26 as an output
echo "out" > /sys/class/gpio/gpio26/direction

count=0

time=120

let count=$time

for (( ; ; ))
do
if grep -q "closed" /proc/asound/card1/pcm0p/sub0/hw_params; then
# echo "DAC IDLE"
let "count++"
else
# echo "DAC Playing"
count=0
fi
if [[ $count -gt $time || $count == $time ]]
then
# echo "Amp Off"
echo "0" > /sys/class/gpio/gpio26/value
count=$time
else
# echo "Amp ON"
echo "1" > /sys/class/gpio/gpio26/value
fi
# echo $count
sleep 1
done

More Info at http://www.runeaudio.com/forum/auto-amplifier-on-off-t928-10.html

Date Votes

10 comments

0

HiFiBerry team May 29, 2016 14:42

Hi Trevor,

thanks for this. I din't even know that the /proc filesystem has entries for the playback status. Cool!

Best regards,

Daniel

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pedroapero July 17, 2016 12:16

Hi,

I'm looking for something similar to power on/off my external integrated amplifier (the one I'm plugging the hifibery output RCA in).

I would wire a 10amp solid state relay to be able to switch on or off an AC power plug using some GPIO, as seen here (works with only >3v input).

I'm using the DAC model for raspberry pi B. Since it's plugged on all GPIO pins, I see two solutions:

- re-use one of hifiberry used ones using a stacking header component like this one (requires unsoldering/soldering the DAC) and still figure out which GPIO pin I can use. It's mentioned here that the DAC uses only the pins on the P5 but I'm sure that can't be true (at least power pins are used on the P1).

- plug the SSR directly on the DAC: in the DAC description is mentioned «Flexible configuration options for output connectors». On the DAC, I see «P3» with two holes marked «5v» + and -, and near the pi's manually soldered P5 connector, I see what seems to be holes to plug another GPIO connector.

What's the proper way of using connectors located on the DAC board to use external components?

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Trevor Cockayne July 17, 2016 12:25

For what I recall the hifibberry team publish what gpio pins the dacs use so you can avoid a conflict

big hint please publish every pin required to make the dac work if not directly connected

as for solid state relays they are wonderful but check the current consumption if your buying them off ebay most are totally fine some i have had pull silly current

i dont use the hifiberry now i have build my own preamp /dac /controler usinng a odroid xu4 and a dual mono dsd 1796 dac so i cant test mine

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HiFiBerry team July 17, 2016 13:12

@Pedroapero: On the "old" DAC, only P5 is used.
If you use the newer DAC+, check out this document:

https://support.hifiberry.com/hc/en-us/articles/205376201-GPIO-usage-of-HiFiBerry-boards

Best regards,
Daniel

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pedroapero July 18, 2016 18:10

Thanks for the quick replies!

@HiFiBerry team: if the DAC only uses the P5, why does it have a P1 connector at all? Do you suggest me to unsolder the P1 from the DAC to be able to access it? Or are they linked to the 12 holes on the top of the DAC?

Edited by pedroapero July 18, 2016 18:17

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HiFiBerry team July 18, 2016 18:12

It uses P5, NOT P1. P1 is used only to provide enough mechanical stability. I would not recommend to unsolder P1, but solder cables onto the pins you want to access.

Best regards
Daniel

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pedroapero July 18, 2016 18:22

I mistyped sorry. OK that's right, there is only one screw hole on this part of the rasp. I'll try that, thanks!

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B G L Nelissen January 11, 2021 12:01

Hi all,

I was looking for this and have made some changes to the script I wanted to share. For my home automation I mainly use MQTT, but I was not able to quickly get MQTT to work on HiFiBerryOS, so I used http GET via wget. My setup:

1. RaspberryPi with HiFiBerryOS and a HiFiBerry DAC+ connected to my amplifier which is used as an AirPlay client.

2. My amplifier is powered via a MQTT controllable relay

3. My home server (NodeRED) can listen to http GET requests and can convert them to MQTT and so controls the power of the amplifier.

How it works:

1. The script runs every 1 second and detects if the DAC is used.

2. When the DAC is used it sends an http GET request to the home server which than powers on the amplifier via MQTT

3. When the DAC is not used it sends an http GET request to the home server which can than decide to power off the amplifier. I have chosen for a delay of 1 hour before switching the amp off.

The script in `/usr/bin/hifipower`

#!/bin/bash

# B. Nelissen

# use /proc to see if card is in use, send status to url

# based on Trevor Cockayne trevoml@gmail.com https://www.runeaudio.com/forum/auto-amplifier-on-off-t928-10.html

#

# this script is run by serviced every x seconds

#

# it keeps an eye on the DAC status

# when DAC status is changed, send message to server for further handling (mqtt etc)

# when DAC status is not changed for x seconds, send message to server for further handling (mqtt etc)

# set variables, create tmp file when needed

DAC_STATUS_FILE="/var/tmp/hifiberryDACstatus"

if [ ! -f "$DAC_STATUS_FILE" ]; then printf 'off' > "$DAC_STATUS_FILE"; fi

CURRENT_DAC_STATUS="$(< /proc/asound/card0/pcm0p/sub0/hw_params)"

PREVIOUS_DAC_STATUS="$(< $DAC_STATUS_FILE)"

SECONDS_BETWEEN_SERVER_UPDATES=60

# main logic

if [[ "closed" == "$CURRENT_DAC_STATUS" ]]; then

# DAC is off

DAC_STATUS='off'

if [[ "on" == "$PREVIOUS_DAC_STATUS" ]]; then

# status changed, from 'on' to 'off', update file, send notification

printf "$DAC_STATUS" > "$DAC_STATUS_FILE"

wget -qO- "http://10.0.0.100:1880/mqtt?hifipower=off"

fi

else

# DAC is on

DAC_STATUS='on'

if [[ "off" == "$PREVIOUS_DAC_STATUS" ]]; then

# status changes from 'off' to 'on', update file, send notification

printf "$DAC_STATUS" > "$DAC_STATUS_FILE"

wget -qO- "http://10.0.0.100:1880/mqtt?hifipower=on"

fi

fi

# seconds since last modification

lastModificationSeconds=$(date +%s -r $DAC_STATUS_FILE)

currentSeconds=$(date +%s)

if [ $SECONDS_BETWEEN_SERVER_UPDATES -lt $((currentSeconds - lastModificationSeconds)) ]; then

# time since last update is more than x seconds

printf "$DAC_STATUS" > "$DAC_STATUS_FILE"

wget -qO- "http://10.0.0.100:1880/mqtt?hifipower=""$DAC_STATUS"

fi

Do not forget a `chmod 755 /usr/bin/hifipower`

The service `/etc/systemd/system/hifipower.service`

[Unit]
Discription=Automatic HiFi Power Control
After=network.target
StartLimitIntervalSec=0

[Service]
Restart=always
RestartSec=2
ExecStart=/usr/bin/hifipower

[Timer]
OnBootSec=5
OnUnitInactiveSec=1s

[Install]
WantedBy=multi-user.target

Edited by B G L Nelissen January 11, 2021 12:08

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HiFiBerry team January 11, 2021 12:07

DO NOT PUT ANYTHING ONTO THE SYSTEM PARTITION!
You will loose all these files with the next update.

For things like this, a docker container should be used - even though this is more complex.

Also don't assume that the HiFiBerry sound card is always card 0, this might change (e.g. if you plug in a measurement microphone before booting).
I would recommend a more generic check:

cat /proc/asound/card?/pcm?p/sub?/hw_params

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B G L Nelissen January 11, 2021 12:09

Thanks for the heads-up! Good to prevent copy paste for future users!

(A http request url for 'play'/'not play' in the UI would be nice)

Edited by B G L Nelissen January 11, 2021 12:11

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