been a bit busy and it's been slow--came back from vacation a short while ago. a couple of friends of mine said they'd start working on it with me after they come back from vacation in a couple of weeks, so it might speed up. Unfortunately, it's going to be quite a while before something solid comes out. atm I'm waiting for a digikey order to come in and then I can start working on the digital section,.
So far, here's the plan:
basics:
- modular design (probably storage module, microcontroller module, USB module, user interface module, and DAC/SPDIF module). This will ease development, debugging, soldering, and allow for customizability. For now I'm using SIP sockets, but later I'll look for something that takes up less space and might be a bit nicer in terms of the parasitics
- onboard diagnostic debug lights (after looking at how many connections there are on the board, this would be pretty darn necessary for debugging)
- (might be removed if I end up needing more board space for everything else) optional built-in BDM programmer for myself and developers for easier debugging
- (might, but probably won't, change) hammond 1455Q1601 case (about 6"x5"x2"--a bit thick, but personally I think the LCD would have to be too small otherwise)
- scf5250 microcontroller, as discussed before
- basic eeprom-based bootloader (more fail-safe than a hard drive based bootloader, at least during initial development)
Basic modules:
- storage: 2.5" HD
- USB: ISP1561 / cypress peripheral controllers for the USB (depends on whether or not I can get samples)
- DAC: WM8740 (digits might be mixed up) for the DAC. I might even use something simpler--the DAC board is modular, anyway, so it doesn't really matter what I stick in here for the first revision.
- SPDIF: directly from the scf5250, with a simple reclock circuit
- user interface module: bunch of tactile play/pause/stop switches, and a simple graphic LCD. I would have gone for an OLED, but it appears that some serious problems are cropping up with supply--optrex, one of the most accessible suppliers of OLED screens, just completely pulled out of the display market. digi-key is only stuck with a couple if tiny OLED modules left in inventory and most other OLED module manufacturers have discontinued their lines. Sparkfun does have a color OLED available from a different OLED screen, but it's a bit more complicated than necessary (color screen) and a bit smaller than I was hoping for. If anyone knows somewhere I could get a monochrome (or grayscale) OLED with a module size of around 60mmx45mm-ish, tell me!
Things on hold for future revisions of the board (i.e. "feature creep" section):
- ultra-low jitter clocking - I've figured out some way to get less jitter than probably anything available commercially. It's pretty complex, though, and I'm almost certain that I can't avoid four-layer boards if I really wanted to implement it. The clock distribution / clocking IC also sucks up quite a bit of power, though, and would probably require another microcontroller to control all of the clocks.
- CPLD for 24-bit audio; the SCF5250 only supports 20-bit. I'm not sure if it'll be really that important, though, as some people seem to think going over 16/44.1, the original format of the audio, isn't a good idea anyway.
- flash-memory based bootloader
- differentially driven expansion port using RJ45/CAT-5 wiring: connect other modules (maybe video out, DSPs, ethernet, DACs slaved to the clock line, etc. . .)
- compactflash/securedigital storage module: the SCF5250 already has controllers for these formats, and some people might not mind sacrificing storage space for less EMI/RFI that might come from the hard drive
- capacitive touch sensor for front panel interface
- nicer screen
- built-in headphone amplifier for the front panel
- movie playback
- enough feature creep already!
As you can see, I'm trying hard to make it as simple as possible =) hopefully this will make it a bit easier for me to actually come out with something in a reasonable amount of time, and make debugging a lot easier.
hm... whoa--sorry for the uber-long post!
