I agree, that there are a lot of Raspberry Pi related postings in the last time, that do not look like audio related postings. But I can tell you – they are. We’re working on audio projects for the Raspberry Pi. The goal is to have a high quality sound system based on a Raspberry Pi. One thing, that we could not find somewhere, was a simple template for a Raspberry Pi extension board. Therefore we created one. The board size is the same 85x56mm as the Raspberry Pi itself and it includes the extension headers P1 and P5. P5 is especially important for audio, because that’s the I2S header. The template is available freely on Github.
The ADAU1442 from Analog Devices is a very interesting chip. It is powerful enough for many audio processing tasks and not too expensive. However DIYers don’t use it very often. Why? There are some problems:
- The chip comes in 100-lead TQFP package and is not easy to solder.
- External DACs and ADCs are needed to add analog audio – the chip itself is purely digital and has no analog input and outputs
- The Analog prototyping module costs more then 600$ which is too expensive for most DIY tests
- There are not many DIYers that think they can program a DSP by themself.
The last problem is not a big problem, because Analog provide the Sigma Studio IDE that allows to create all kinds of digital filters and creates the DSP software for you.
Why not fix the other issues? We’re thinking about a prototyping board for the ADAU1442. It would include
- the DSP chip,
- some analog inputs and outputs (not sure about this, because it will consume a lot of space on the PCB),
- a power supply,
- an I2S interface to add external I2S devices (even a Raspberry Pi might be an option),
- an interface for a microcontroller, and
- pin headers to put it on a breadboard
What do you think? Would you like this kind of board?
Today, the design of the HiFiBerry sound card PCB for the Raspberry Pi has been finalized. Expect a prototype in the next weeks. The HiFiBerry will not only provide high quality audio output for the Raspberry Pi, but also a stereo input. Due to the limited space, we will not have PCM inputs and output jacks, but only a pin header. If you want to use PCM input or output, you can simply add some cables to the board connecting to external connectors.
Update 1: The picture does not show the final version. I realized (very late), that the chip is in a SSOP package and fixed this.
Update 2: We’re testing the prototype now.
Our first test for the comfortINA starts – controlling the amplification of an instrumentation amplifier by a switched resistor. The DigiPot uses two low-resistance analog switches (ADG451) and an 8-bit shift register. The shift register is used to simplify external connections to a 2-wire serial bus (DATA & CLOCK). On board LM317L/LM337L reduces the external +/-18V voltage to +/-15V. For the tests we will use our platINA board and the control will be handled by an Raspberry Pi.
Our popular platINA PCB is now available in two colors: the classic green PCB and a blue version. Except for the color, both PCBs are identical. The blue version looks really cool if you use red WIMA MKP capacitors on it.
Are you looking for other colors? Tell us!
Do you design your own printed circuit boards? Even 4 layer boards can be done by hobbyists today relatively cheap. For simple analog circuits, it is not very difficult to design a circuit that works well. But what about mixed analog/digital circuits? Or analog boards with lots of small components? Do you need 4 layers or is a two-layer-board enough? How should you route power supply lines? What about a ground plane? There are lots of things to think about. Here are some links to documents that can help you to create better PCBs:
- TI: PCB design guidelines for reduced EMI
- Tim Jarvis: Best practices in PCB design
- Linear: PCB Layout Considerations for Non-Isolated Switching
Power Supplies while it focusses on switching power supplies, some concepts are also useful for mixed analog/digital circuits
- TI: Circuit Board Layout Techniques
- AD: Printed circuit board design issues