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Old 12th March 2013, 07:07 PM   #21
davada is offline davada  Canada
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Quote:
Originally Posted by GeorgeBoudreau View Post
I suggest the first kick at the can would be to build the simpler, single AK5388 mono-design shown in Fig.1 of the app note. It has a simple mux for the output and puts off the fussy FGPA work until later.

It would allow the creation/testing of the analog input stages , clocks and power supplies. The output of the card would be plain vanillia I2S. Theoretically the card should be able to mate with any I2S engine, commercial or open-source.

George
Hi George,

Yes the idea is for the card to able to mate to any I2S. I would like it to be stand alone if possible. I would prefer what ever technology is used is in a form I can work with and have access to. And if someone else wants to dig into it for there own purpose they are quite welcome to. There is nothing more frustrating to a DIY to be dependent on someone else for up grades or a certain amount of interest just get to a board. After all it's DIY.

Cheers,
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Last edited by davada; 12th March 2013 at 07:21 PM.
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Old 12th March 2013, 07:54 PM   #22
1audio is offline 1audio  United States
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I have the AKD5394a board and could connect it to the audiowidget board. I would be happy to try it. I need some insight as to which pins on the the module to connect to get it running? The demo board has oscillators and dividers so the necessary clocks and data are available. Do I need to connect I2C? The I2S connections should be pretty straightforward.

I can easily graft different Input circuits. I'll use the QA400 interface board as a starting point to try things.
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Old 12th March 2013, 08:12 PM   #23
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Quote:
Originally Posted by 1audio View Post
I have the AKD5394a board and could connect it to the audiowidget board. I would be happy to try it. I need some insight as to which pins on the the module to connect to get it running? The demo board has oscillators and dividers so the necessary clocks and data are available. Do I need to connect I2C? The I2S connections should be pretty straightforward.

I can easily graft different Input circuits. I'll use the QA400 interface board as a starting point to try things.

You can pull up the connection I/O for Borge's boards on his site at Q N K T C USB-I2S Module and Analog Board

However, I do not believe the firmware for the Audio-Widget supports ADC input. ( I could be wrong )

George
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Old 12th March 2013, 08:16 PM   #24
borges is offline borges  Norway
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Hi Demian,

does your board run out of the box in some recognizeable mode? If you don't need to do an awful lot of configuration, leave the I2C.

Assuming you're using an AB-1.2 class thingy to start with: MCLK-wise I'd recommend you to tap MCLK from the AB-1.2 and patch it into the AK board. The USB-I2S module receives clock commands from the PC. You can choose 2x.xxMHz at the XOs or a 2^n division at the dividers you so wisely had me put in :-)

Alternatlively, you can change the USB descriptors to only reflect the sample rates your AK board operates on. Then you'd need to send MCLK in the opposite direction. There should be plenty of places where you can strap things in on the AB-1.2.

Let me know which HW you start out with on the USB side of things, and I can try to give you some patching guidance.

BÝrge
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Old 12th March 2013, 08:18 PM   #25
borges is offline borges  Norway
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George, you are right, the audio-widget branch of the firmware does not support the ADC.

The ADC is selectable through WidgetControl. One option is to add ADC functionality from the SDR-widget branch into the audio-widget branch, and use the WidgetControl setting (or a Makefile define) to maintain DAC-only compatibility. Unfortunately, I'm not the guy to do that coding work just now.

BÝrge
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Old 12th March 2013, 09:13 PM   #26
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Quote:
Originally Posted by borges View Post
George, you are right, the audio-widget branch of the firmware does not support the ADC.

The ADC is selectable through WidgetControl. One option is to add ADC functionality from the SDR-widget branch into the audio-widget branch, and use the WidgetControl setting (or a Makefile define) to maintain DAC-only compatibility. Unfortunately, I'm not the guy to do that coding work just now.

BÝrge

Porting the ADC component of the SDR-Widget to the Audio-Widget is not trivial. The SDR-Widget AK5394A card is tightly coupled to the Atmel processor and does more than support the I2S signal. All of the ADC sample-rate, calibration etc is driven or monitored by the cpu. To turn the Audio-Widget into a pure I2S slave, AK5394 code is set for master mode, you would need to hack quite of code.

Demian, grab the SDR-Widget document archive for the schematics on how the ADC is set up.

George
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Old 12th March 2013, 09:58 PM   #27
1audio is offline 1audio  United States
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I'll dig into that later this week. I have an extra audio widget (AB1.2?) module that I got from Borge some time ago for this project. I had a sense it would not be as simple as connecting a few wires. However it seems its not as onerous as it might be.

The AKM demo board has the I2S breakout and the other connections to enable a quick patch to test all of this. I have really not used the audio widget on Windows yet so that is a separate task for me. How different is the SDR widget code from the audio widget? To use the SDR widget code what needs to be done in broad terms?
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Old 13th March 2013, 05:30 AM   #28
1audio is offline 1audio  United States
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A quick summary of what I need to do to connect the AKD5394a to the QNKTC I2S module (I think):

1) Connect I2S lines at follows:
TP62 to port 3 pin 3 (L/R clk)
TP62 to port 3 pin 2 (Bit clock)
TP60 to port 3 pin 4 (Data)
TP36 to port 3 pin 1 (mclk at 12 MHz)

I will leave the board fixed at 192 KHz. (I presume that bit clock and L/R clocks are outputs from QNKTC)

What do I need to do to get a firmware that will run this and something that Windows will recognize as an audio source? (Hacked driver??)

Attached are clips from the documents for my reference as much as anything.
Attached Images
File Type: jpg AKD5394A I2S.JPG (37.7 KB, 111 views)
File Type: jpg QNKTC USB Pinout.JPG (88.2 KB, 110 views)
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Old 13th March 2013, 05:19 PM   #29
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Are you all planning on having some kind of input attenuation and/or high voltage DC blocking for this ADC? Some of the tube guys might want to measure the THD on the plate of some tube or other high voltage device.
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Old 13th March 2013, 11:59 PM   #30
1audio is offline 1audio  United States
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I would use a probe concept to manage different applications and dynamic requirements. Making it autorange etc with protection against overload, really low internal noise etc. is way more complex than the device itself. AC coupling at the input makes sense and differential attenuator probes can handle voltage issues. Easily swapped for direct input probes for low level signals.

I have designed most of the necessary protection stuff and its more real estate than the circuit itself. That's why I abandoned that approach. I can dig it out if there is interest.

For the purposes of discussion here is a really crude block diagram of the components of a system.

A few notes on the diagram-
1) USB power, this enables running entirely from the batteries on a laptop, eliminating AC noise issues. We may need two USB power sources to support everything. We can probably only count on 2.5W per USB connection.
2) DAC and ADC isolated from each other, again eliminating common ground noise issues.
3) Master clock isolated as well and transformer coupled, this does a good job of keeping loading and power noise from affecting the jitter of the oscillators
4) I show a block for DSP for mixing multiple ADC's. For realtime stuff, like recording, this may be useful for improving the system. For measurements we can use averaging schemes to do something similar, possibly.
5) We will probably need I2S controls to both the ADC and the DAC.

Its conceivable that we could add autoranging and use the host micro to manage it and report back to the PC the current gain ranges etc. However then the PC application would need to manage the info. It can get out of hand really quick. See above.

If we break it down then the blocks can be addressed individually making the project less overwhelming. I'll post what I have done so far when I find it all.

Its quite possible to dump parts of this but in the long run limitations will arise.

This won't be real cheap to build. But the performance would potentially be on a par with the best commercial stuff.

Input and output levels-
I would go for a fixed output of 3V RMS max, again a passive attenuator can scale it down and 3V should drive any typical amplifier to clipping.
Input of 3V RMS which is close to the actual differential input limit for the chip. Adding a preamp of 40 dB will extend the low level of the system. I figure a practical noise floor of 100 Ohms equivalent (1.2 nV/rtHz) would be the limit and 40 dB of gain will move the preamp noise floor approx 15 dB above the ADC. 40 dB is nice for arithmetic but other settings are an option.

Comments?
Attached Images
File Type: jpg ADC Block Diagram.jpg (45.2 KB, 96 views)
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