To trim and MP3 use

ffmpeg -ss <START> -to <END> -i input.mp3 output.mp3

Where and are the start and end of the song you want, in seconds.

The Raspberry Pi Pico in the momobox is not capable of playing high-bitrate MP3s! The momobox also only has one speaker, so it's recommended to convert songs to mono prior to loading onto momobox. The following command is recommended:

lame -b 128 -m mono input.mp3 output.mp3

Remove the SD card from momobox, and mount the SD card to your PC using an SD card reader. As of this writing it is not possible to access the SD card through your PC while it's installed in momobox.

Simply copy the MP3 files to the SD card.

This process is a work in progress - some utilities need to be written to make it smoother.

Connect the momobox to your computer and go to the serial console by running

screen /dev/ttyACM0

Attach the new momie to the momobox. You should see an error like this:

Making RFID request
Found RFID key: 88047126
That song isn't registered!

If this is the first time adding songs to the momobox, create a library.txt file for the library index.

Copy the RFID key (88047126 in this case) and add the following entry to a new line in library.txt:

<RFID KEY>, /sd/<NEW_MP3_FILE>,

An example library.text file looks like this:

88046318, /sd/wildthings.mp3
8804710a, /sd/greeneggs.mp3
8804635b, /sd/peppa.mp3
88047126, /sd/cat_in_the_hat.mp3
88047108, /sd/mickey_mouse_mono.mp3
88047116, /sd/wheels_mono.mp3

Save library.txt and upload it to the momobox. This should restart the momobox, and the new MP3 file should be registered.