[sdiy] Digi-Mod extra optional features ..?

[Seb Francis]

I'm very near to finishing the layout of my 'Digi-Mod' board.  For those 
who haven't seen the previous threads, this is a generic PCB to make 
digital modules for modular synths.

The basic features are:

- dsPIC33FJ128GP708 (40 MIPS)
- High quality audio CODEC (2 channels in, 2 channels out), with 
switchable sample rate
- 4Mbit SRAM (5.6s sample time at full sample rate)
- Analog feedback loop with CV control (using THAT2162 VCAs)
- 14 CV inputs (2 to VCAs, 12 to DSP)
- 8 Analog Gate inputs
- 10 Digital I/O pins (3.3V logic levels, including 2xSPI, 1xI2C)
- MIDI In/Thru/Out
- 8Mbit EEPROM to save samples, etc.
- ICSP/ICD connection

Obviously it will be capable of many different things, but the (open 
source) software I plan to write will give the following 4 modes of 
operation:
http://burnit.co.uk/sdiy/stuff/Digi-Mod-Controls.html

So that's the overview.  I'm aiming for plenty of flexibility to allow 
people to come up with other interesting uses/software for it, and many 
of the parts are optional so they can be omitted if not required (e.g. 
the SRAM, VCAs, MIDI I/O, EEPROM, etc.)

Having now almost completed the PCB layout except for routing the main 
digital stuff, it's clear that there's space left for some more 
options.  I've already made the PCB small enough to fit almost all 
modular racks (it's 105mm high x 98mm deep), and I can't really shrink 
it any further because of all the I/O headers.

See all the space left ... the joys of SMD :)
http://burnit.co.uk/sdiy/stuff/Digi-Mod.png

So what extra options to add??  My only thoughts are an SPI multi-output 
DAC for CV outputs.  Any other ideas?  And while I'm asking .. any 
recommendations for a suitable DAC requiring minimal external components?

Here's the schematic of the whole thing so far:
http://burnit.co.uk/sdiy/stuff/Digi-Mod.pdf

Seb