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freeDSP V2.0 (ADAU1452) developement thread
freeDSP V2.0 (ADAU1452) developement thread
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Old 9th February 2015, 08:31 PM   #11
Pitrsek is offline Pitrsek  Czech Republic
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Default Back to ribbon

I was considering using SATA due to its size and the possibility to use stacked connectors to save space. As it turned out, stacked SATA connector is "unobtanium". I've used ribbon cables in my last serous build (a team project built for a student competition, I've attached picture of it). I did not grow fond of ribbon cables and connectors, alas there is nothing better(price,space,performance). So back to ribbon cable.... Due to size of connector, last in/out channel will not be placed at the pcb edge. I've started to work on schematics and libraries, but progress is quite slow.
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File Type: png idea2.PNG (67.7 KB, 1120 views)
File Type: jpg _DSC3766.jpg (911.3 KB, 1178 views)
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Old 19th February 2015, 03:22 PM   #12
CharlieLaub is offline CharlieLaub  United States
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Any progress/updates or thoughts on this project?
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Old 19th February 2015, 08:44 PM   #13
Pitrsek is offline Pitrsek  Czech Republic
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Default power supplies,I2C

Hello Charlie, yes, there is some progress. I've been busy researching power voltage regulators. I've settled on single supply for all - separation between noisy and sensitive circuitry will be facilitated by separate regulators. My selection:
1.2V and 3.3V for logic - LM3370SD-3021
3.3V for PLL and Aux ADC - LP5907

Hopefully I'll be able to make pcb universal, either for single clock crystal - connected to ADAU, or with two NDK oscillators, clock selection and ADM7150(for oscillators). So one can choose whether need/want high quality clock or prefers to save some money. We will see if it's possible when I'll start to design the pcb, but I'd really like to do it.

As for opamp power supply, it seems to be either TPS7A3301 and TPS7A4701 or jung regulator. When you use quality voltage reference and opamp, you are not that far away from price of TPS. I have en eval board for TPS on the way, so I'll know more when it arrives.

I've decided to go with i2c - mainly to save GPIOs. The drawback is that total delay time is limited to 800ms for 48kHz(If you go with SPI you can attach additional memory for longer delay times), but I believe this would be enough for any loudspeaker xover.

Input/output IDC connectors will contain I2S,I2C, 5V and maybe 3V3. Connection made(I2S,I2C, clock selection, reset..) to RPi header will be provided on additional IDC connectors, so you can connect any MCU/SBC you wish. There will be an I2C switch, so you can choose to which(slave/master) I2C line you want to talk to, additionally I2C lines going to Input/output IDC connectors will be buffered.

I have ADAU1452 with me, if I can find suitable thin coax, I'll measure its package capacity.

As always, I'm open to suggestions and critique.
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Old 25th February 2015, 11:04 PM   #14
Pitrsek is offline Pitrsek  Czech Republic
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Default Just a small update...

Tps eval board has arrived, haven't played with it yet.
I've spent quite some time on I2S/Output connectors. I ended with the configuration in attachment(it does not represent pin-out, just which signals are presented).

With this arrangement, you have a choice between 1x4 or 2x2 or 4x1 - inputs and outputs. OUT3/IN3 connector will be shared with RPI. You can connect 8ch usb streamer, or 8ch BBB, or rpi and wolfson SPDIF and still have some inputs left. Or 8ch BB and wolfson SPDIF(if you decrease Fs of BBB)... this is the most versatile arrangement of the connector I've been able to come up with.

I've stumbled upon an interesting IC - TPS65131. If I use it(with post regulation), I could power whole thing from a single 5v adapter. A smaller, more streamlined design.

I'm thinking about using toslink instead of BNC. Why? If you are interested in audio, chances are that you are already using USB to I2S, or using clock sync, so vanilla SPDIF is not really interesting for you. On the other hand, it seems that everything has toslink nowdays - cheap pc motherboards, gaming consoles, even some laptops...

Comments are welcome.
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Old 6th March 2015, 09:12 PM   #15
Pitrsek is offline Pitrsek  Czech Republic
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Hi, I've managed to destroy TPS during impedance measurement - probably too strong signal from VNA. Some of schematic sheets are complete, some are still missing few bits. I started with PCB layout, it seems that the board will be a bit longer than 120mm. The progress is kinda slow, but at least it is quite steady.

I'm having difficulties getting my hands on new 8ch DAC from AKM, I still got quite some time before I need it, so hopefully it will be available at that time.

I hope that I'll be able to share the schematic and some ""work in progress" layout next time.
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Old 6th March 2015, 09:33 PM   #16
mhelin is offline mhelin
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Any ideas why Analog recommends 4-layer PCB for the ADAU1452? They say on their forum (https://ez.analog.com/thread/47216) it's because of thermal reasons, but isn't it just possible to circumvent somehow (using lots of vias under the chip or something).
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Old 10th March 2015, 10:46 PM   #17
Pitrsek is offline Pitrsek  Czech Republic
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Default 4layer board

If you sum up all of the expenses(and the time!) for a project with ADAU1452, you will see that difference between 2L and 4L, compared to the rest, is really small. You will route 2L board longer and will have to make a lot of layout compromises. Your ground-plane will look like an emmental cheese. I'm not saying it is not possible(especially for application with somehow limited IOs), just that I don't believe layer count is good place to save $. Heat is the least problem - you can always slam heatsink on/under it.

Price difference between 2 and 4 layer board is around 30$. Surprisingly, it is same with local fab house and with popular online batch services as well. You can pick if you want 10pcs and wait... or are in a hurry and need one fast.

On related note, going from 4layer to 6layer is only 15$... which translates to something like 10 beers in a pub. Yes, we have a cheap beer...

If you decide to have a shot at it, I can send you my design files(Altium Designer).
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Old 15th March 2015, 07:07 PM   #18
basreflex is offline basreflex  Spain
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LT just brought out the LT3042 utralow noise regulator. interesting for osc , pll supply ..
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Old 17th March 2015, 12:01 AM   #19
doctormord is offline doctormord  Germany
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I've done like so:

http://www.diyaudio.com/forums/class...ml#post4259585
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Old 22nd March 2015, 04:34 PM   #20
Pitrsek is offline Pitrsek  Czech Republic
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Default Long overdue update

Nice board doctormord

Thank you basreflex for heads up on new ldo from LT, I wasn't able to find a place where you can buy one, lets wait and see. I'm a bit skeptical about the price.

At the moment, power supply for XO is provided by ADM7150, and for PLL by LP5907(this is shared with Aux ADC supply). Another LP5907 powers optical receiver.

About the board:
This will be a first and not the final version of the board. The aim is to test and evaluate the stuff. So there is a lot of connectors, jumpers, etc.
Generally the idea is to make this board as universal as possible (within reasonable bounds). This will change with next version, which will be more streamlined and polished. This brings me to another point - ATM BBB is quasi supported. What does it mean? I've connected I2s 3 header after buffer for RPI.So connection is buffered and can be disabled. Unoftrunatelly, I don't know weather BBB uses bclk and lrck as inputs or outputs.
Since my primariy interest is RPi(yay for quad core Pi ), I don't file like searching 100+ long thread to discover the connection.
If there is someone interested in running ADAU1452 with BBB please check wather my connection is right or wrong. Thank You.
At the moment, I2c from MCU header is not isolated, so for safe operation with BBB one would need to add I2C buffer with enable - so rise your hands who is interested in this feature .
If there's a PCB space, I might add the buffer(and change the other one to model which supports daisychaining).


About I2C
There are two I2c busses, on first bus there is:
DSP as a slave
I2C buffer to bridge two busses, with automatic reset of DSP - this is mainly for developement purpose, so I can talk to EEProm and DAC directly.
Port expander with open drain - to facilitate reset, enable, mclk switch, enable to I2S to RPi - on startup states on RPi GPIO are not guaranteed, so I've opted to use I2c expander
LM3370SD - you can enable spread spectrum
Master is connected either via RPI connector or USBi/BBB/MCU connector

Second I2S bus contains DSP as a master and AD/DA converters as a slave, and the bridge. I've decided not to include I2C fan-out buffers for AD/DA converters

I've included screenshot of work done on PCB and schematics. Neither is complete(both are rough drafts), and there are probably some mistakes. It's work in progress on all fronts, but now you have a better idea about the project. I hope You like it.
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File Type: pdf SchematicsA.pdf (328.9 KB, 252 views)
File Type: pdf SchematicsB.pdf (194.4 KB, 189 views)
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