PIC24 based drum machine

This is my interpretation of a "classic" 16 step multi-pattern drum machine based on a microchip pic24hj128gp502 running at 40Mhz.

It has up to around 16 instruments and has 8 sample polyphony. The song length is limited by the available RAM in the pic but is quite compact so can easily have song of 16 patterns or more. The audio output is a mono 156khz PWM signal that is low-pass filtered and fed to a TI audio amp.

I currently have 11 instrument samples loaded that are converted from samples of classic drum machines found on the web like the Lin LM-1 and Roland 808. The maximum number of instruments is limited by available memory space and depends on how long each sample is. The samples are normalised, trimmed to be as short as possible and then converted down to 8bit 16khz mono using Audacity.

The PIC used has 128kb of flash which gives around 80kb free for samples after the main program. The software was originally developed for a more common PIC with 64kb (pic24fj64ga102) but I soon ran out of space for decent samples so I moved to the biggest pic24 that you can still get in 28pin DIP. Moving to the larger high-speed (h) series PIC also brought a faster clock speed which allowed for a higher frequency PWM which improved the audio quality.

There is a rudimentary pattern save and load feature utilizing a FAT16 formatted SD card. The patterns are encoded as a JSON structure and saved as a text file so are editable in a text editor if you felt like it.

CD card is driven via SPI using FAT functions provided by ChaN's FatFs library.
JSON parsing is handled by a heavily pruned version of Dave Gambles cJSON library.
Nokia 5110 is driven via SPI using a library of my own creation.
Maxim 6957 LED driver is also driven via SPI using my own library.

I had/have lots of plans for this, including a better user interface and the ability to load samples from the SD card but unfortunately have not had much time in the past year to actually work on it that much.

So rather than allowing it to fade away I'm showing it to you now in the hope that someone is interested.