HD Audio from ground up (Part 3)

Following the Part 1 and 2, it is time for the last hardware oriented post of this blog series. Future blog posts will follow covering the software aspects of the project with some libraries and reference designs.

The Audio module (that includes the TLV320AIC23B DAC) is ready and tested and the best way to present and play with it (except from the regular breadboard) is the creation of a new board! The idea was to build something that includes common storage options for the audio files (or any other files!), Ethernet communication, and some user IO (2 buttons and two potentiometers). As an extra some H bridge drivers were included for controlling some actuation, quite often needed in industrial audio applications. As always, the important factors are the total cost of the board and how easy it is to recreate. This means no fancy SMD components and not a design specification pushed to the limits (Figure 1). 

The euro card size (160x100mm) was selected for the design for four main reasons:

1. There is enough space for all the components, and for a clear descriptive silkscreen layer.
2. The dimensions create a nice visual image to the viewer (it is based on the golden ratio formula a/b = 1.6 = φ).
   
   
3. If you want to place the board into an enclosure there are a wide variety of plastic and metal boxes exactly at those dimensions, which are low cost too as it is a standard size.
   
   
4. If you don’t want to use a PCB manufacture shop then you can etch your board at home into a standard size photosensitive board without the need for a saw!

 
For the peripheral modules the audio board includes:

1. An Ethernet connector
2. A host USB type A connector
3. The HQ DAC module
4.  A micro SD card
5. Two 6x6mm tactile push buttons
6. Two single turn potentiometers
7. Motor / Solenoid driver
8. Four PWM outputs

The top silkscreen layer designed with the easiness of use in mind. The user can check the connections between the mbed and the peripherals and relate this to the program code, without the need to check a full schematic diagram. Furthermore, the connections are grouped together into small “bubbles” forming the digital protocols that can be used for the communication between the peripherals.

Pin headers have also been placed inside the bubbles for easy probing with oscilloscopes and logic analyzers (like the USB one used for the debugging and verification of the libraries that will discussed in the coming posts). When laid out like this, the debugging procedure is easier for a non experienced user.

The final touch (yeah, I am speaking like an artist but a PCB layout is a kind of art sometimes) was creating the logos. I wanted to include the two tools that help me to create this audio demonstration board. First the Design Spark PCB for the free design tools and second the mbed that powers the board.

The logo of the mbed was easy. By using the text tool of the layout editor and the right text font, the logo was ready. After that, the placement and size was the only considerations. But the logo of Design Spark (the open loop antenna) was a complicated story. It is not a solid object but consists of small lines (creating the sparkling effect) of different lengths and thicknesses. It is not just difficult to create something like that in the silkscreen layer, but it is also difficult for the design software to handle the amount of vectors.

Together with those problems I have to pay attention to the manufacture constrains of different PCB production shops in order to find a middle point between an excellent result and the cost of the board. The job will be easier at a cooper layer but it is not creating the same visual effect, and that why the idea dropped from the beginning.

Of course, after an hour of work the logo was ready and the actual result is more than impressive considering the abilities of the manufacture shop. You can see a close up of the two logos together in the Figure 2. And trust me, the real PCB looks even better!