Switching Inputs on the Twisted Pear Audio Buffalo III-SE DAC

One of the neat features of the Buffalo III-SE is that it allows you to have both a SPDIF and I2S source connected and to switch between them using the on-board IP_S pins, thus obviating the need for an OTTO or other external switching mechanism. And if you’re controlling the BIII-SE with an Arduino you only need to use a single (digital) pin to switch between sources. Turns out it’s very easy to implement, but I couldn’t find any guidance on the web.

The following assumes that you have a SPDIF and I2S source connected the BIII-SE (block “1” in the picture below). ALl you need to do is connect a digital pin (I use pin #6) on the Arduino to the pin below the “S” on the IP_S header on the DAC – circled in red in the picture below with a red arrow pointing to it.

The code is simple as well.

Put this in your initialization block:

  #define IPSPIN 6 // Or whatever pin you're using
  pinMode(IPSPIN, OUTPUT);
  digitalWrite(IPSPIN, HIGH); //Enable pull-up resistor - default is SPDIF

And then just switch the pin HIGH when you want SPDIF and LOW when you want I2S.

If you’re using the HiFiDuino code, then just swap out the setAndPrintInputFormat function for this one:

void setAndPrintInputFormat(byte value){
  // This register also controls mono-8channel operation, thus more code...
  lcd.setCursor(8,0);
  switch(value){
  case 0:                            // Enable SPDIF for DATA 1 pin
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x01);        // Set SPDIF to input #1 (only input valid for BII is 1 and 5)
    spdifIn=true;                    // Indicates input format is spdif. 
    lcd.print("SPd");
    break;
  case 1:                            // Enable SPDIF for DATA 3 pin (For BIII use)
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x02);        // Set SPDIF to input #3 
    spdifIn=true;                    // Indicates input format is spdif.
    lcd.print("Sp3");
    break;
  case 2:                            // Enable SPDIF for DATA 7 pin (For BIII use)
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x40);        // Set SPDIF to input #7 
    spdifIn=true;                    // Indicates input format is spdif.
    lcd.print("Sp7");
    break; 
  case 3:                            // Enable SPDIF for DATA 7 pin (For BIII use)
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x80);        // Set SPDIF to input #7 
    spdifIn=true;                    // Indicates input format is spdif.
    lcd.print("Sp8");
    break;
    
  case 4:                            // I2S 32 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitClear(reg10,4);               // Setting to I2S (2 bits required)
    bitClear(reg10,5);
    bitSet(reg10,6);                 // Setting to 32 bit (2 bits required)
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("I2S");
    break;
  case 5:                            // LJ 32 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,4);                 // Set to LJ
    bitClear(reg10,5);
    bitSet(reg10,6);                 // Set to 32 bit
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("LJF");
    break;
  case 6:                            // RJ 32 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified format
    bitClear(reg10,4);
    bitSet(reg10,6);                 // Set to 32 bit
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R32");
    break;
  case 7:                            // LRJ 24 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified format
    bitClear(reg10,4);
    bitClear(reg10,6);               // Set to 24 bits mode
    bitClear(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R24");
    break;
  case 8:                            // LRJ 24 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified format
    bitClear(reg10,4);
    bitSet(reg10,6);                 // Set to 20 bits mode
    bitClear(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R20");
    break; 
  case 9:                            // LRJ 16 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified mode
    bitClear(reg10,4);
    bitClear(reg10,6);               // Set to 16 bit mode
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R16");
    break;   


    // lcd.write(127);                    // Print Arrow to indicate this is input seletion and not signal
  }

  if (spdifIn) { //If we're expecting SPDIF input, we want to pull IPS high on the DAC 
    digitalWrite(IPSPIN, HIGH); 
  } 
  else { //If we're not expecting SPDIF, pull IPS low
    digitalWrite(IPSPIN, LOW);
  }
}

Thanks to LeonvB and the folks at TPA for talking me through the process.

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Hacking an Arduino Library to support a NewHaven OLED with an MCP23008 port expander

 

After looking at several sample Buffalo DAC projects I decided that I didn’t like the LCD screens most people were using. I had a Sansa Clip a few years back that used a very crisp OLED display – a quick search on Mouser and I found an inexpensive 20×4 NewHaven OLED (NHD-0420DZW-AY5-ND) that looked like it was  HD44780 compatible.  

It isn’t.

After reading a bunch of forum posts complaining about this display, I stumbled across someone who had tweaked the standard Arduino LiquidCrystal library to make it compatible with the OLED timing parameters: http://www.elcojacobs.com/controlling-an-oled-character-display-with-arduino/.  I swapped his library for LiquidCrystal and – huzzah! – my DAC was humming along with a beautiful OLED display.

The next step was to minimize the number of pins I was using on my Arduino using an I/O port expander.  By using the two i2c pins (A4 and A5) on the Arduino, a port expander gives you 8 outputs.  The downside is that the port expander makes things considerably slower – too slow to be usable.  So I was excited to find the LiquidTWI library as it promised to speed things up by “bursting” all 8 pins at once, rather than trying to address each pin serially: http://blog.lincomatic.com/?p=956.

And it worked!  Sort of.  I had to tweak the timing parameters again, but Elco had already shown me how to do that.

Everything worked perfectly except for custom characters – which is something the HiFiDuino code uses to display the volume.  You might be able to print one or two custom characters, but the display would ultimately go into WTF mode and you’d have to restart it.

I tried a very long “delay()” when custom characters were being written, but regardless of how long I waited, nothing helped.  As far as I could tell, the problem has something to do with the D7 pin on OLED display, which serves both as an input to the OLED and an output that indicates when the DAC is busy.  According to the datasheet, you are supposed to poll the busy pin and only write a command when the busy pin tells you the OLED has finished processing.

So, by hacking the Adafruit MCP23008 library, I was able to implement a function that reads the busy pin.  We only need to use this function when we are writing/creating custom characters, so it really doesn’t slow things down too much.  And the library takes care of invoking the function when necessary, so it’s invisible to anyone using the library.

BUT, BUT, BUT …

The volume display is tied to the movement of the rotary encoder, which uses an interrupt to indicate when it is being turned.  It seems the delay that the readBusy() function creates wreaks some havoc with the rotary encoder functionality, so a quick spin of the encoder doesn’t register.  So after all that, I’ve reverted back to directly connecting the OLED to the Arduino.

But maybe somebody else can benefit from the library I wrote.  If so, grab the code here: https://github.com/tharmas/LiquidJWM