Aud-I/O I2S audio breakout

[Bertho]

Hi all,

I am working on a project that requires some real audio and I always wanted to play with I2S (attached to an arm microcontroller). So I decided to design a breakout board with stereo audio input and output(*). It uses a Wolfson ADC WM8782 and a Wolfson DAC WM8523. All configuration pins are available on the SIL headers. The headers are at 2x10x100mil with 700mil spacing, so it should be possible to dump it into a breadboard. The breakout board can be split into a DAC and ADC part, each measuring 21.6mm by 45.1mm.

Comments?

PCB gerberview

(*) sparkfun only has an ADC afaics and that is not in stock.

[bearmos]

I started noticing i2s on a shared SPI peripheral (part of an stm32 I'm using currently). Not having looked into it, I'm assuming it's basically SPI with a standardized protocol?

I've done the same types of breakout boards before (easily breadboardable) - it never ceases to amaze me how long I used them after the initial development. Having a few modules that can easily be thrown together on a breadboard in a few minutes makes tryng out new ideas so fast there aren't any excuses as to why something can't be done ;-).

Looks good so far - any plans on sharing the rest of the project?

[Bertho]

I started noticing i2s on a shared SPI peripheral (part of an stm32 I'm using currently). Not having looked into it, I'm assuming it's basically SPI with a standardized protocol?

Yes and no. It is a serial protocol, but it runs with a few extra signals like left/right clock (which is the actual sample rate), master clock (128..1024 times sample rate) and then the standard datastream and bitclock. The data format is also much more complicated running between 16 and 32 bits and modes to left/right adjust the datastream (to interleave multiple chips on a bus). Not all formats are called "I2S", though, but most microcontrollers with basic I2S support can cope with many of the formats.

I've done the same types of breakout boards before (easily breadboardable) - it never ceases to amaze me how long I used them after the initial development. Having a few modules that can easily be thrown together on a breadboard in a few minutes makes tryng out new ideas so fast there aren't any excuses as to why something can't be done ;-).

That was exactly my thought. These breakouts make it so simple to hack something together that you can get a yes/no for a project very fast.

Looks good so far - any plans on sharing the rest of the project?

Absolutely! The project is open, but not yet documented. I'll upload the schematics in a separate post. At least it will be somewhat documented this way ;-)

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Greetings Bertho

[bearmos]

bearmos wrote:Looks good so far - any plans on sharing the rest of the project?

Absolutely! The project is open, but not yet documented. I'll upload the schematics in a separate post. At least it will be somewhat documented this way ;-)

Cool, looking forward to it. I've found that it's funny how easy it is to post progress on projects in forum threads. Probably due to the informality of the forum vs something like a web page. Of course, it also helps to have such a great community here ;-)

I just tried documenting a project for the first time as it unfolds here and it's been great - both in the questions/comments and "hey, you forgot xyz!", which is exactly what I was hoping for.

I find that, since I really like to take screenshots and "show" as I'm telling, a screen capture utility helps quite a bit. A freebie for windows is gadwin print screen, which makes taking screenshots of selections as easy hitting print screen, dragging the selection and (optionally) naming the file.

[Bertho]

Here are the schematics of the design.

The PCB got changed a bit removing the linear regulator. There was really no point of having it because the digital io is 3.3V. The supply should already be available in the system as most of the ARM systems run on 3.3V anyway. This is a small compromise for the ADC because it can handle a higher voltage at AVdd for better audio input performance, but it is not worth the trouble imo.

Audio out

Audio in

Combined in a PDF:

aud-io_sch.pdf

Schematic pdf

(19.09 KiB) Downloaded 105 times

New PCB view:

Gerber view

[joushou]

Interesting - I'm curious if I could get these to work with the latest revision Raspberry Pi boards that will be shipped soon (I only ordered them half a year ago... But they got upgraded to the newer 512MB ones, so I suppose it's OK...). I'm far from satisfied by the PWM sound experience, and I don't want USB to fire any more needless interrupts... I2S sounds like a proper solution (Yay for the addition of full I2S to the GPIO on rev2 pi's <3)

[Bertho]

(Yay for the addition of full I2S to the GPIO on rev2 pi's <3)

Well, if the I2S signals are available, then there should be no problem. It is then a matter of setting it up or creating an alsa driver.

--
Greetings Bertho

[kasbah]

Did you ever get this made?

[Bertho]

Did you ever get this made?

Yes, I did get it made. However, it is still not tested (properly). My colleague who was to write software for it still has not finished. He is working on it, but he can almost only use Tuesday evenings (hackerspace meetings) to get the code to run, so this is progressing at snail's pace.

Pcb mounted top

Pcb mounted bottom