You can now play MP3 files directly in CircuitPython with no dedicated decoding hardware! You'll be able to use this new capability in all sorts of projects, including this creepy Lars the Sloth voice box project!

The benefit of MP3 over other non-compressed file formats, such as WAV, has always been their small file size, meaning you can pack a lot of songs or samples into limited memory. However, decompressing those small files for playback was too taxing for older microcontrollers, so we had to use dedicated decoder chips at an additional cost, including licensing fees.

Thanks to the raw speed of M4, the days of requiring a dedicated MP3 audio decoder chip are behind us. And, since the patents have expired, we can now distribute MP3 playback libraries free of charge!

Parts

Who is Lars?

Lars is the sworn enemy of CVT Joseph, the ice cream truck godfather of Los Angeles, and owner of  CVT Soft Serve.

Lars is angry that Joe won't reveal the location of his Wonka-style Golden ice cream gift cards. This video linked below will make everything clear:

https://www.instagram.com/p/B--_P8JJWWy/

Actor Matt Biedel (Umbrella Academy, Narcos) has kindly given us permission to use Lars's voice. At least that's what Joe claims.

To use with CircuitPython, you need to first install a few libraries, into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.

Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory MP3_Tap_Player/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.

Your CIRCUITPY drive should now look similar to the following image:

Text Editor

Adafruit recommends using the Mu editor for using your CircuitPython code with the Feather boards. You can get more info in this guide.

Alternatively, you can use any text editor that saves files.

Code.py

Copy the code below and paste it into Mu. Then, save it to your Feather as code.py.

Audio Samples

You can get started by using these .mp3 files. (Of course, you're free to use any files that you like, see below for more info on that.)

Download the .zip file linked below and then uncompress the file. Drag the /lars directory onto the root level of your Feather's CIRCUITPY drive.

Make Your Own

To make your own .mp3, use audio software such as Audacity to save them with these settings:

• bit rate: anywhere from 16 to 320 kb/s (lower will be smaller, higher is better quality)
• sample rate: 22050Hz or 44100Hz are recommended, although 16kHz, 24kHz, and 48kHz should also work
• channels: mono or stereo
• must be DRM free

How It Works

Here's what the code does:

• Imports the necessary libraries for audiomp3 playback and accelerometer tap detection with the adafruit_lis3dh
• Sets up the accelerometer
• Specifies the speaker enable pin (this allows the speaker to be disabled when not in use)
• If startup_play is set to True, each sample in the /lars directory with the name format of /lars_0*.mp3 will be played using the mp3stream object
• In the main loop of the program, the accelerometer is checked for tap detection. When the tap occurs, the next sample is played. When the tenth one is played, the list loops around back to the first one again.

Test It

With the enable switch clicked on, try tapping the Feather/Propmaker to trigger a sample. When a sample has finished you can tap again to trigger the next one.

Note, there is a small volume adjustment screw on the Propmaker FeatherWing that can be turned with a small screwdriver to adjust the maximum volume.

Now, let's add the sound player to our puppet friend Lars!

You can now plug a USB cable into Lars's foot for battery charging, swapping out .mp3 files, or even adjusting the CircuitPython code!

Test out your finished puppet now by making sure the Enable switch is clicked on, then tap his back to play!

You may need to wiggle the speaker around to get it to an optimal placement. Also ensure the battery is charged or the USB cable plugged in to get sufficient power.

Note, in the video below I was using a double-tap to trigger.