While writing up how SD cards work, and reading files using FAT16, we’ve also been developing our little audio board a bit further. We got as far as playing audio files from our SD card and fitting them to the alarm clocks for a tester project the other day.
We’ve now taken the project one stage further, and introduced serial/uart support.
So rather than play a file immediately, you can send serial commands to the audio board.
- # – send back a list of all files found in the root directory
- | – pause playback
- > – resume playback
- – half current volume (max four times)
- / – double current volume (to max)
At any time you can send in a filename over serial.
If the filename is in the format xxxxx.yyy (where xxx is any string up to 8 characters and .yyy is a full stop followed by a three-character extension) the chip will search the root directory for a file with the same filename and extension.
If a file is found, it begins playing immediately.
If the chip is in the middle of playing a wav, the current wav file is stopped, the current sector is closed, and the chip plays the new sound from the start.