The DAC development platform

[mako1138]

There's an I2C controller available from opencores.org:

http://www.opencores.org/projects.cgi/web/i2c/overview

Just hang it off the microcontroller, like how it is in a PIC or AVR. Using Microblaze to bit-bang strikes me as inefficient.

Alternatively, writing your own I2C controller would be a good exercise. It's not that hard, but there are enough issues to make it "interesting".

[duddface]

I was offline(literally) for the last few days and came back to Civilization and WWW just now.

peufeu,

What I actually meant asking you was whether you have decided on which drive strength to use for your I/O drivers. Choosing the "optimum" drive strength for Signal Integrity. The Spartan-3 devices let you choose 7 different drive strengths ranging from 4, 6, 8, 12, 16, and 24 mA, when you decide if it going to be either LVCMOS or LVTTL I/O standard. The optimum being either 8mA or 12mA drive strength.Anything lesser than would be wimpy. The reason why this would be of great interest to you would be to keep EMI low by choosing an optimum drive strength along with slow output slew rates. This is totally independent of the layout and can be done either before or after your board is laid out. All it takes is different FPGA bit streams for you to decide which drive strength suits your needs.

There is actually a free I2C I/P available at Opencores??.That is spiffy.

Happy new year guys.

[peufeu]

Yeah, OpenCores is nice.

So far we have :

- SPDIF IO Board : done, ready for review.

I modified the layout a bit, did some signal integrity simulations, everything should be OK.

- Cheap FPGA module : done, ready for review.

XC3S500E, no Ethernet, 16 bit SDRAM, XCF Platform Flash, Atmel DataFlash, connectors for : Digital IO board on one side, Reclocking/DAC on the other, JTAG, LCD, buttons, etc. Board will be 4 layers with standard tolerances, so not that expensive or risky to make. Signal, Ground, VCC, Signal. Lots of decoupling caps, resistors in the IO lines, etc. See notes on schematics. I will do the harder BGA once this one works, to have Ethernet and more power.


- Clock / Reclocking board

Schematics done.

- DAC board for AK4396 : done, ready for review.

I happen to have one of those, and it's voltage out, so it will be simpler for the first try. And it's supposed to sound good.

- Filter for AK4396 (Bal -> Unbal and Lowpass)

Schematics done. Placing done, with DIP8 opamps (socketed) and multiple footprint caps (ie. those have several holes to fit many styles of caps).

So, before starting to solder stuff, I still need :

- Layout of Clock and Filter boards
- Power Supply
- Regulators

Get all the files here :

http://home.peufeu.com/nik/dac/DacPl...2008-01-02.zip

On the Clock, DAC, and Filter boards I will put some regulators. Those are on pin headers. I will use a symmetrical 10-pin header so the regulators can be plugged both ways in. Also 3 pins doesn't secure much anything physically to the board, so the thing may fall off. 10 pin is better
Obviously though, it will be advised not to swap a +15V reg for a +5V reg to avoid smoke !

The power supply will provide +/- 15V via dumb LM317 so regulators can be replaced by a simple bypass. It will also provide the unregulated voltage on the rail caps so the regulators installed by the user can start with more than 15V to get 15V in the end.

Phew !

I'm looking forward to when that thing is going to be finished !

[peufeu]

News :

Everytime I touch this it seems I had forgotten something. The other day I realized I had forgotten to level-translate one of the lines from 3.3 to V. Anyway.

- I added a connector for an ADC. I have an AK5393 sample...
- I touched up the boards with more relaxed design rules (I'm thinking about having the boards made in china or something).
- Place & route for everything that was waiting is done.

I just need to make the power supply.

I'll post the last version of the stuff tomorrow, I think.

Yay !

[ralphs99]

Hi Pierre,

I've just sent my comments to you. I hope you find them helpful.

Cheers, Ralph

[peufeu]

Yes, thanks !

Update :

OK. Many, many changes since last time. I redid the layout of the FPGA module (looks much better now), added a module (CDP slaver). Look at the notes in the schematics

Here : http://home.peufeu.com/nik/dac/DacPl...-12_rev0.2.zip

I'll be unavailable for a week, then I'll have to do the power supply board, and order parts.
Do you have suggestions for the PSU ?

See ya

[AR2]

Are you are going to make boards for this that we could order?

[peufeu]

That's the whole point, yes
It's supposed to be a collaborative project with people sending DAC, IV etc modules in the mail. So at some point that should happen...

[duddface]

If you think that you might want some insurance by choosing a switcher instead of a linear, then go for it.Switchers are really good for high slew rate loads such as FPGA cores,processor cores because of their excellent transient response. But again, There are a few crummy details to look at. Switchers tend to put out beat frequencies which are at random harmonics of the fundamental switching frequency. These could extend all the way down the audio range unfortunately. This prompted to Synchronize the switcher to some multiple of the system clock, so that the frequency components are within a known spectrum thereby making the output filtering simple. There are plenty of these available from Linear Tech. Some of these are monolithic meaning the Top Fet is integrated and all you need to supply is the inductor, input bulk,bypass and output bulk and ferrite beads for pi filtering. Some of these can provide upto 5Amps peak.

[nicoch58]

Like this?

http://www.linear.com/designtools/re...sign/index.jsp