Inspiration

There is a video game where you play a hacktivist seeking to eliminate big brother’s influence over Chicago. Over the course of the game you get a large collection of devices which James Bond would be proud of. One of my favorites is the Lure. This is a small device which occasionally emits a sound to attract enemies and allow you to sneak by.

I always though this would be a fun project to build and after watching a few too many ghost hunting videos I thought it would be great to have a device which could also spook a paranormal investigation team by having the ability to play longer sounds and “creepy” noises.

GOALS

Small – Easy to Conceal
Loud enough to be heard from far away
Battery life of 12-24 hours to allow you to place and recover device
Play MP3, OGG WAV and other standard audio formats. Do more than chirp
Not rely on external wifi/networking
Triggerable from a phone
Use as little custom hardware/code as possible.

A General Note – This is not a commercial product, in many cases I take shortcuts to make this work as simply and quickly as possible (Remember the site is called My Bodge). Since the end goal is to have a device which does not live on my network, I am ignoring best practices for network security, software design, common decency, and most of all common sense. Just have fun with the project, feel free to vent in the comments and I will feel free to ignore you. Relax… it will be ok if you don’t scrub your inputs just this once…. I won’t tell.

Components

Hardware

Rasberry Pi – A raspberry pi has both wifi and Bluetooth connections for control. They can act as a wifi hotspot to access remotely and has a native ability to play sound files in a variety of formats. I used a RPi 3+ but any model should work as long as its accessible from wifi.
SD Card – I used a 32gb sd card, but really you can go smaller without an issue.
Audio Hat (optional) or Powered Speakers – the full size Pi has a headphone jack which you can connect to powered speakers but a Pi Zero does not. Thankfully, a number of clever people have created this already (I used the WM8960 board – https://www.amazon.com/gp/product/B08CCV3XVZ/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1) but there are others out there.
Power – I used an Anker Power Core 10000mah usb powerbank. On the Raspberry pi 3b it lasted 24 hours with a decent amount of playbacks occurring. No special reason you need this battery, I just had a couple handy, battery size has a direct impact on how long the Pi will stay on.
Container – I am 3d printing a container for this project but there is no reason at all for you to do this. This project will happily work in a spare tuperware or plastic bin.

Software

Rasbian aka Raspberry Pi OS – Just grab the latest
Apache2 – Again the latest
PHP – Just grab version 7.21.b/6…. no other…. Really nothing will work unless you manage to find this mythical version of php… oh wait never mind, just grab any version which mod_php in apache supports. Don’t worry we will cover exactly how to do this.
Omxplayer – Raspberry pi audio player – Should come with rasbian.
Drivers for Audio Hat (as appropriate)
Audacity (for adjusting levels on the sounds files)

Steps

Follow the steps for setting your Raspberry pi

Connect to the raspberry pi using the ssh command

Install apache

sudo apt-get install apache2 -y

Install php and the apache plugins

sudo apt-get install php -y
sudo apt-get install libapache2-mod-php -y

Change to /var/www/

cd /var/www

Change the owner of html to pi:pi

sudo chown pi:pi html

Update apache to run as pi:pi

sudo nano /etc/apache2/envvars

Within the editor change the lines APACHE_RUN_USER=www-data to APACHE_RUN_USER=pi

Change the line APACHE_RUN_GROUP=www-data tp APACHE_RUN_GROUP=pi

Restart

sudo restart

Test the web server

From your computer try bringing up the default page for your pi

Launch a browser and bring up http://<your pi hostname>.local If you needed to use an ip address to ssh to your pi, use that to bring up the page.

Now lets confirm that php is working correctly. Enter the following command

sudo nano /var/www/html/test.php

Enter the following line <?php phpinfo(); ?>

Save the file then bring the file up in your browser by navigating to the same url as the last step plus /test.php

You should see the following. Don’t worry if your version is different

At this point you have a functional web server running on a computer. Congrats

Making noise

If you are using the built in headphone jack for sound skip till the “Playing a Sound” section

Install git

sudo apt-get install git

Grab the audio drivers

git clone https://github.com/waveshare/WM8960-Audio-HAT

Change to where the newly downloaded files

cd WM8960-Audio-HAT

Install the hat drivers and restart

sudo ./install.sh
sudo reboot

aplay -l

Check to make sure the sound board appears

Playing a sound

If you installed the full version of Raspberry PI OS this step can be skipped. If you installed the light version we need to install the Raspberry Pi audio player OMX Player.

sudo apt-get install omxplayer

Change to the following directory

cd /var/www/html

Create a directory to hold sounds

mkdir sounds

change to that directory

cd sounds

Download a sample file

wget http://www.mybodge.com/wp-content/uploads/2021/03/whistle.wav

Play the file

If you have an audio hat use

/usr/bin/omxplayer --no-keys -o alsa:hw:1,0 --vol 1000 whistle.wav

or if you are connected to the headphone jack on the pi use

/usr/bin/omxplayer --no-keys -o local --vol 1000 whistle.wav

Troubleshooting

Volume – There are some known issues with the WM8960 and its ability to support the command line volume. I have found that louder sound files are frequently distorted. The example files with this article have had their volumes lowered to accommodate this.
No Sound – Check that your card is listed via aplay -l. If it is not reach out on github to the audio hat drivers issues board.

Finally the app

The basics of Version 1 of this application is

User connects to the pi and displays a list of sounds to play
User Clicks on a button to select a sound
Sound plays via the omxplayer app. Basically trigger the same command as we used to test the sound when the user clicks on a button.

Build the app

Switch to the html root directory

cd /var/www/html

Remove the default apache page

sudo rm index.html

Copy Sounds

This file has a set of sound files for your use. Unzip the files into a directory of your choice

Open a local command prompt, change to that directory and run the following

scp * pi@<your pi’s address or name>:/var/www/html/sounds

This will copy the files to your newly created sound directory.

For the first version of this app is a simple php program. Going through a detailed introduction to php is beyond the scope of this article and honestly has been covered to death elsewhere. In a nutshell php allows you to mix code and html together to have a programmatically generated webpage.

In this case we are going to create a new page (index.php) which will have a title at the top then list all the files it finds in our sound directory as a set of buttons. When a user clicks on a file button it will run the omxplayer command using the filename from that button

Create the index page

sudo nano index.php

Enter the following

<html> 
<head> 
<title>Distractor</title> 
</head> 
<body>   
<form method="get" action="index.php"> 
	<div >
		<center><h1>Distractor</h1>
        <?php 
			// 1. OPEN THE SOUNDS DIRECTORY
  			 if ($handle = opendir('/var/www/html/sounds')) 
			 {
				while (false !== ($entry = readdir($handle))) { // 2. LIST THE FILES IN THIS DIRECTORY
					if ($entry != "." && $entry != "..") { // 3. SKIP THE SYSTEM . and .. FILES
					  echo "<input type='submit' value=".$entry." name='fn'/><br/> "; // 4. FOR ALL OTHER FILES CREATE AN HTML INPUT BUTTON WITH A VALUE OF THE FILENAME and a name of fn
					  
					}
				}
				closedir($handle); // 5. CLOSE THE DIRECTORY HANDLE
			}
		?>
		</center>
    </div>
</form> 
<?php
    if(isset($_GET['fn'])) // 6. IF THIS PAGE IS POSTED WITH AN FN ARGUMENT PLAY THAT SOUND
    { 
        $fullpath = '/var/www/html/sounds/'.$_GET['fn']; // 7. ADD THE FULL PATH TO THE PASSED FILENAME
        $cmd = '/usr/bin/omxplayer --genlog --no-keys -o alsa:hw:1,0 --vol 1000 ' .$fullpath.' &'; //8. PLAY THE SOUND
        shell_exec($cmd);
    }
?> 
</body> 
</html>

The html components of this file should be familiar to you. The PHP commands which this file are running do the following

Open the sounds directory file to get a list of files. This returns a file object (also called a handle).
For each file found …
If its a system file ignore it
Create an html submit button with the filename as the value
Close the file handle object
If the user clicks the submit button the page will reload with the fn parameter set. If its set
Add the full path to the passed filename
Please the sound using the OMX Player command

Try it Out

Launch a browser and bring up http://<your pi hostname>.local If you needed to use an ip address to ssh to your pi, use that to bring up the page, You should now see a list of sound files in a simple interface.

Clicking on a sound should start playing it.

Troubleshooting

It is entirely possible that the first time you create this page something will go wrong. Thankfully there is a text log created in /var/logs/apache2/error.log. Take a look at this file and it will usually point you at the line(s) which are the cause of your grief.

Conclusion

This is part one of a series. The next part we will clean up the look and feel of our page a bit and create the ability to upload new files and terminate playing sounds. We will also change the device to be its own WIFI hotspot and not rely on an existing network.

For a list of where these great sounds came from please see attributes on part 2 of this series.

Source for Part 1 can be found here