Lots of stuff to talk about here, some very good points raised, first power supply:
I'm thinking of a single 5V supply, such as for the Touch, on the standard connector. Thus a basic swither could be used or one of the aftermarket ones if desired. I would be glad to come up with one of my linear designs for this is which could be an option for it. At this point I have not done any research on the best wallwart to use with such a project, there are a lot out there, maybe after Gen1 boards go out different people can do some experimentation and come to some conclusions. The grounding and noise issues etc are a very interesting aspect of this, what I am planning on doing is the following: the board will have two power domains, digital and analog. The digital domain has the processor, memory, ethernet, USB etc. The analog domain has the DAC chip, headphone amp, S/PDIF out, audio MCLK oscillators and reclocking flops. Each section will have it's own separate ground plane, with the few signals going between them going through isolators (I prefere the GMR types, I HATE ADUMS). There is a separate plane which just has the raw +5 and ground from the power supply, this plane connects to the two domains in one place for each domain. This scheme does a very good job of prevening digital domain noise from getting into the analog domain and still lets you power the whole thing off of a single supply. What makes it work is that there is one and only one ground connection between domains, this prevents any ground loops from happening. Since I am planning on an eight layer board I can put signal routes between planes, which does a good job shielding, cutting down on EMI. Cases: Norm you are right, I was just going to screw the Gen1 board onto a pice of plywood for my own use. I can certainly design it to fit a case if we can find own that works well. I want to keep the edge that has the connectors to 3" so I can get all the connectors on there. I like the slide into extrusion concept, I have used it many times. One variaton I have done is use PCBs for the end panels, the board makers have the soldermask available in many different colors and silkscreen can handle labels etc. One interesting technique I use is to put holes in the soldermask so the underlying glold plating shows through, you can do logos, model name etc with this that REALLY look nice. I did one with blue solder mask and the gold showing through that was stunning. The price can be less than laser cut aluminum, and they can look quite striking. Board testing: the manufacturing place I use automatically does bare board testing for multi layer boards to make sure the boards were done right. They also automatically do X-ray testing of BGAs to make sure the soldering came out right. They CAN do assembled board electrical testing. Simple testing is included in the price. They can do more extensive testing if test points are included on the board, but of course that costs more money. The big problem is that it takes a lot of time to come up with a good comprehensive test program. I don't think I want to do this for Gen1, but it's probably a good idea for Gen2. They have experts that will work with you to design a board that's easy to test. Again, probably not for Gen1, but probably a good idea for Gen2. On the memory front, the AM3874 has two DDR controlers, so if we use two 256MB chips we get twice the memory throughput, it's tempting. My original thought was to limit the design to one memory chip since putting two chips on the same controller is MUCH more difficult. But since this processor has two controllers I don't have to deal with that, I can do two chips without the extra hassle. I think you guys have convinced me that it's probably worth doing it. On the why do this in the first place? For me the motivation is that I can integrate quite good sound into the product for a LOT less money than it takes to do an equivalently good USB async DAC. The processors I'm looking at already have kernel drivers for audio over I2S and S/PDIF. These are available free from the manufacturer in their SDK which should make sending data to the DAC chip and S/PDIF not too difficult. Yes it is going to take some work, but I don't envision it being too bad. That brings up the issue of other external interfaces (remotes, IR blasters etc). I'm kind of leary about putting those directly on the board. They WILL require kernel drivers to be written and frankly I'm not convinced that is going to happen. I think we need to crefully look at this issue and come up with a workable solution so that separate kernel drivers do not need to be written for each interface. USB can be used for a large number of these, it might be a lot easier to come up with a GPIO over USB approach to add these. Anyway I'm not going to add these in Gen1, we as a community need to spend some significant time coming up with how to deal with this issue of other external world interfaces. I hope that covered all the recent quations. On another front, the BeagleBone is coming today, so hopefully I will have some results of hooking up USB DACs in the next couple days. There are SDcard images for at least 10 different distros for this board, it will be interesting to see what happens. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=97881 _______________________________________________ discuss mailing list discuss@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/discuss
