INTRO

This blog has been sort of a notebook for me to write down my own learning with Arduino and the TPA boards. Therefore the information presented assumes that the reader’ is learning at a pace equal to mine.

Beginners are overwhelmed with the amount of information here so this post is to help those by outlining the basics of building a controller board for the superb kits produced by Russ and Brian of Twisted Pear Audio. TPA is also developing a controller for their products so this is an alternative to their solution utilizing low cost, and widely available parts. (As of July 2011  April 2013, the TPA controller board in not yet available, so this is the only “ready-to-run” option)

Basically, all modern audio chips have a software interface and they communicate with a micro-controller through a communication protocol called “I2C”. I have chosen the Arduino platform because I am not a programmer and Arduino is geared towards that audience. In addition, the Arduino community provides a lot of help for beginners and non-programmers.

HIFIDUINO is about building a controller that can talk to those audio chips. So far I’ve interfaced to the OPUS DAC with the WM8741 and the Buffalo II boards. But the same platform can be used to interface to other chips such the WM8804 spdif interface and even the brand new TI PCM51x2 DACs with lots and lots of features that are available only through s/w programming.

The controller consists of:

Arduino board

NOTE: if you use Arduino UNO R2, there is a potential bug: http://hifiduino.wordpress.com/code/#comment-718

Any official board or clone will work. The current (v.09) code size is about 14K bytes, so even the bottom of the line Arduino will work. All of he following models work: UNO, Dueminalove, Seeeduino v.2.2, NANO and others. I have used the UNO and the Dueminalove. I have even used the Freeduino. If you want to be dead sure that it will work, then purchase the latest official Arduino UNO (R3 or above)

The Freeduino with a companion stationary shield

Rotary encoder

The rotary encoder is used to change volume and settings. In theory, you can use any “quadrature” or “gray code” encoder. However, I find that the preferred characteristics of the encoder are:

• About 30 cycles per turn. This gives a good “feel” when changing the volume, changing 30 db per revolution -not too fast or too slow
• Built-switch. The switch is used to change from volume control to DAC settings control. This is not mandatory, you can implement with a separate switch
• A rotary encoder with “clicks” is preferred because you can feel the clicks when you select the different settings. I tried a rotary encoder without “clicks” and it does not work well because selection of the different settings take advantage of pushing the encoder to activate the switch. Often one you push the switch you can also inadvertently move the encoder. Rotary encoders without detentes (“clicks”) are not recommended.

I use a Panasonic model that has been discontinued, but available from Electronic Goldmine. Other candidates are: Bourns PEC11, BI EN12. The current version of the code (v.09) does not require that you build a debouncing circuit as the debouncing is done in the software (I had used the rotary encoder without hardware debouncing or a long while, but I finally added the debouncing capacitors).

• More on debouncing: link
• Here I recommend the “most suitable” rotary encoder: link

LCD display

The code assumes a 20×4 LCD. Any LCD that is compatible with the HD44780 protocol will work with the code: Do a search for “20×4 LCD HD44780″ on eBay. The one I purchased is from Sure Electronics. You can also purchase directly from their website: [link]. Nowadays it is available pretty much everywhere. Here is another good source: iTeadStudio

As it turned out, a larger portion of the code is the user interface and it assumes a 20×4 LCD. Thus, if you use a different form-factor LCD (for example a 16×2 LCD, you will have to overhaul a lot of code.

NOTE: if you use Arduino UNO R2, there is a potential bug: http://hifiduino.wordpress.com/code/#comment-718

IR receiver and a remote control

The code supports the Apple Aluminum Remote. Any IR receiver should work. However, I would recommend the Vishay TSOP32438 because it is designed for the 38KHz frequency used by the Apple Remote. The 32438 model also provides noise immunity. Additional information: [link]

Here is a good article on “how to choose IR receiver”: [link]

In fact, any one of these would work:

TSOP32338SS1V

TSOP32438SS1V

TSOP38238SS1V

TSOP38338SS1V

A level converter from 5V to 3.3V for the I2C lines

This part maybe optional. As the I2C inputs of the Buffalo are “supposed to be” 5v tolerant, but the data sheet does not say specifically and I have not determined that to be the case with 100% certainty. (You can easily build it if you do not wish to buy the module)

You can build your own level shifting by following this diagram from this document [link]

I Made my own here: [link]

GET GOING

The best use of this project is for you to experiment with your own choice of components and ideas. You can reuse whatever part of the code you wish (as I have reused code from other contributors. -This is the spirit of open hardware and software of the Arduino community). If you do this you will find that the audio hobby is not just about changing cables, capacitors and power supplies

However, if you wish to just replicate what I have done, this is what you do:

• Get familiar with the Arduino development environment. At the minimum you must know how to compile code and upload to an Arduino. The Arduino tutorials listed in the side bar are a good start.
• Procure the parts above and hook them up according to the different hookup diagrams in this blog. The current code does not require that you build a debouncing circuit for the rotary encoder so you can skip the debouncing circuit
  • IR receiver hookup
  • Rotary encoder hookup (follow the “no H/W debounce” diagram)
  • LCD hookup
  • Level converter hookup
• Download the latest version of the code from the code tab. Compile and Upload to the Arduino
• Done!

This is what my controller looks like:

User Interface summary

Here is a very nice summary of an older (v. 09) user interface from マルチチャネルDAC製作記 blog and in particular this post [link]

I have updated the user interface a bit: http://hifiduino.wordpress.com/2012/01/09/code-compatible-with-arduino-1-0/

Newer versions are a refinement. But the overall user interface is pretty much the same

NOTE: if you use Arduino UNO R2, there is a potential bug: http://hifiduino.wordpress.com/code/#comment-718
EASY ORDER (DIGIKEY)

Arduino UNO R3: 1050-1024-ND [link]

ANOTHER IMPLEMENTATION

Here is another implementation of the controller with a hand made Arduino “shield” to facilitate connections: LCD, Arduino, shield, rotary encoder and IR receiver.

The shield has the following components:

• 5V to 3.3 Level translator with external pull up resistors (1.5K ohm) and local 0.1 uF power supply (5 and 3.3V) bypass. This will ensure clean I2C signals. External pull ups may or may not be required. Depends on your environment.
• Potentiometer for LCD contrast adjustment
• Potentiometer that adjust the current to the base of a transistor controlling the brightness of the LCD
• Arduino reset button (since the reset button of the Arduino is covered by the shield)
• Underneath, I had implemented a debouncing circuit for the rotary encoder. The code does not need the hardware debouncing circuit since it uses s/w debouncing, but it does not hurt.

The external 1.5 Kohm I2C pull up resistors were added afterwards to solve a noisy I2C connection. In most cases, the internal pull-up resistors or the pull-up resistors built-in in the level translator board should be good enough. I had also added power supply bypass capacitors to further clean up the I2C lines.

The h/w debounce circuit was built in accordance to a BOURNS “Signal Conditioning Technical Note” paper [link]. This is not required by the current version of the code because s/w debouncing is used. However, it is always a good idea to reduce spurious interrupts.

Connecting the LCD

Connecting the rotary encoder (with switch)

I find this rotary encoder very good. With solid clicks and good feel. You really need a rotary encoder with “clicks” because it is also used to make adjustment. I had also used an encoder without clicks and as you push the encoder to actuate the switch and make selections, you would also slightly rotate the encoder making inadvertent adjustments.

More info on rotary encoders:

• More on debouncing: link
• Here I recommend the “most suitable” rotary encoder: link

Connecting the IR receiver