Arduino controlled Dual Mono AK4490 DAC (Part 2)

Following up on Part 1, it’s time to talk about the “brains of the operation”. Bare with me, this is going to be a rather long read.Hardware selection

The DAC needed to be controlled by a microcontroller so I looked into my options. I wanted something that would:

  • Be easy to program, so the Arduino IDE was a must.
  • Be able to drive a TFT.
  • Have enough storage capacity to store enough code & fonts for the TFT.
  • Be readily available.
  • Be relatively low cost, since it would have no influence on the dac’s SQ.
  • Be easy to build / integrate into a new design, even by a novice.

After some consideration, I decided to use an STM32F103 ready-made module. It would plug in to a “mainboard” of my design, along with the chosen TFT. It would be fast enough, have enough flash & ram, be easy to integrate and develop for and it would cost next to nothing.

Next up was the TFT. I’d seen on Ebay an interesting one that was relatively big, high resolution and inexpensive. It was this one:

It can be found on Ebay by searching for “3.5 tft uno 320 x 480”. Expect to pay 6-8€ inc. shipping.

After some searching I found a suitable library that (after some slight tinkering) would allow my tiny STM32 to drive it properly. (Note: do not download the library from this link. I will provide a customized version of the library together with my code).

I found a ready-made library for configuring the Si570 and modified it to run on my STM32, using one of its hardware I2C ports. I will also include this library in my code. To complete the recipe I also found working rotary encoder and IR receiver libraries.

The code

Next up was the prototyping work. I adapted my TFT HiFiDuino Pro code to run on the STM32 & TFT combo, with support for AK4490 dual mono operation. The end result had this feature list:

  • Support for either Dual Mono or single chip setups.
  • Support for the Amanero Combo384 USB to I2S module (must be set up as slave with MCLK/2 and F0,1,2,3 enabled).
  • Control with one rotary encoder with push-to-select functionality.
  • IR Remote support.
  • Support for software volume control, from -99dB to 0dB
  • Display incoming signal sampling rate and type, determined by “reading” the relevant I/O pins of the USB to I2S board.
  • Display and control of the AK4490’s digital filter.
  • Selection of the proper MCLK frequency according to incoming SR and type and programming of the Si570 accordingly.
  • Control of “DSD Direct” function of the AK4490s.
  • Control of the DSD Filter’s Frequency (50KHz or 150KHz).
  • Control of the Sound Mode of the AK4490.
  • Choice of either inverted or normal analog output for the AK4490s.
  • Choice of two sets of MCLK frequencies, either 22/24MHz or 45/49MHz.
  • Remote power on/off functionality (or always on – configurable in the code).

Software Requirements:

In the download I am including the modified versions of the libraries (as mentioned above) as well as the necessary font files. Be sure to extract the contents of “Libraries (place in Libraries folder)” to your Arduino IDE’s “libraries” folder.

Download it here: aKduino v2 (880 downloads)

Here is the revision history:

v1.72 24/12/2017:

  • Minor changes to make compatible with current stm32duino core (changed HardWire.h to Wire.h and other minor stuff).
  • First public release as part of completed dual mono DAC project.

v1.66 10/10/2017:

  • Minor volume bugfix.
  • SuperSlow filter still problematic.
  • Enabled DAC synchronization feature (experimental..).

v1.64 30/09/2017:

  • Bugfixes.

v1.60 20/09/2017:

  • Added support of rotary encoder and IR remote control.
  • 3.5″ TFT support.

v1.50 07/01/2017:

  • Added support of rotary encoder for volume control.
  • Bugfixes related to DSD.

v1.41 06/01/2017:

  • Added support for dual mono mode.

v1.36 03/01/2017:

  • Added very basic TFT support.

v1.35 20/12/2016:

  • Code cleanup for first public release.

v1.33 19/12/2016:

  • Added full control of sound parameters through serial port.

v1.27 18/12/2016:

  • First functional version.
  • Automatic switching between PCM and DSD by monitoring DSDPIN.

The “motherboard”

After I was certain that everything related to the software was working the way it should, I designed a “motherboard” that would take care of the following:

  • Accept the STM32F106 board.
  • Accept the 3.5″ TFT.
  • Accommodate an 24LC256 EEPROM chip, used to store the DAC’s configurable settings.
  • Accommodate two sets of I2C signal isolators and I/O expanders.
  • Include headers for the encoder, IR receiver, power relay, non-isolated and isolated I2C communication, unused uC pins, etc.

This is what I ended up with:

Basic Hardware Requirements:

  • STM32F106 module (a.k.a. “blue pill”, search Ebay for “stm32f106c8t6 board”)
  • 3.5″ TFT with resolution of 320 x 480 (Search Ebay for “3.5 tft uno 320 x 480”)
  • 24LC256 EEPROM chip
  • I2C Isolator ICs, I/O expanders, passive components, etc (see BoM)
  • Rotary Encoder
  • IR Receiver
  • Compatible IR remote control (Apple Remote or other – in any case you must edit the code and input the proper IR codes for your remote, see below)
STM32 TFT Motherboard Bill of Materials
PCB Part Value Notes
C1, C2, C3, C4, C5, C6, C7, C10, C11 100n, 0805
D1 1N4001, DO214BA
L2 Ferrite bead, low R, 1206/3216
LED1, LED2 LED 1206
Q1 AO3400, SOT23
Q2 BC808, SOT23
R1, R2, R3, R4, R12, R13 2.2 – 3.3Κ, 0805
R5, R7 2.2K, 0805
R6 5.1K, 0805
R8, R11 1K, 0805
R9, R10 10K, 0805
U1 24LC256, SO-08
U2, U4 SI8605, SOIC-16
U3, U5 MCP23008, SO-18W
DC_5V .100 (2.54mm) – 2 Pin
EXP .100 (2.54mm) – 2×4 Pin
I2C .100 (2.54mm) – 3 Pin
I2C_ISOL1A, I2C_ISOL1B .100 (2.54mm) – 6 Pin
I2C_ISOL2 .100 (2.54mm) – 3 Pin
IR .100 (2.54mm) – 3 Pin
JP1, JP2 .100 (2.54mm) female – 6 Pin
JP3, JP4 .100 (2.54mm) female – 8 Pin
UART .100 (2.54mm) – 3 Pin
MCP_ISOL1 .100 (2.54mm) – 10 Pin
MCP_ISOL2 .100 (2.54mm) – 2×6 Pin
POWER_RELAY .100 (2.54mm) – 2 Pin
ROTENC .100 (2.54mm) – 4 Pin
STM32_BLUE_PILL STM32F103C uC board

How do I make it work?

Power

You have to supply the board with 5VDC at ~300mA through header DC_5V.

DC_5V
Pin Function
+ 5VDC
- GND

Basic connectivity

Serial port:

UART
Pin No. Function
1 RXD (PA10)
2 TXD (PA9)
3 GND

Rotary encoder:

ROTENC
Pin No. Function
1 PB13
2 PB14
3 PB15
4 GND

IR control:

IR
Pin No. Function
1 PB9
2 GND
3 Vcc

If you will be controlling a power on/off relay, you can use the POWER_RELAY header:

POWER_RELAY
Pin Function
+ 5VDC
- GND

Expansion header:

EXP
Pin No. Function
1 3.3V
2 GND
3 PB3
4 PA8
5 PA15
6 PB1
7 PA12
8 PB0

I2C header (non-isolated):

I2C
Pin No. Function
1 GND
2 SCL (PB10)
3 SDA (PB11)

Isolated I2C ports

The board has provisions for two separately isolated I2C ports, complete with I/O expanders on their isolated sides. The idea is to connect the DAC board to one of the isolated ports (I2C_ISOL1 & MCP_ISOL1) and your USB-to-I2S board to the other isolated port (usually MCP_ISOL2)

I2C_ISOL1A(& B)
Pin No. Function
1 3.3V (isolated)
2 SDA (PB11)
3 OUT (PC13)
4 IN (PC14)
5 SCL (PB10)
6 GND (isolated)

MCP_ISOL1
Pin No. Function
1 3.3V (isolated)
2 GP0
3 GP1
4 GP2
5 GP3
6 GP4
7 GP5
8 GP6
9 GP7
10 GND (isolated)
I2C_ISOL2
Pin No. Function
1 SCL (PB10)
2 SDA (PB11)
3 GND (isolated)
MCP_ISOL2
Pin No. Function
1 3.3V (isolated)
2 PC15
3 PA11
4 GP0
5 GP1
6 GP2
7 GP3
8 GP4
9 GP5
10 GP6
11 GP7
12 GND (isolated)

That’s it for Part 2. Stay tuned for Part 3: The output stage.

Comments

comments

23 thoughts on “Arduino controlled Dual Mono AK4490 DAC (Part 2)

    • v1.41 is pretty old.. There’s a good chance it’s buggy or not compatible with the current stm32duino core. I could email it to you (use the contact me link) but if I were you I’d just adapt the current version to my needs. Cutting out stuff is easy..

    • It’s not supposed to be included in the ZIP file because it’s not modified by me. I only include the libraries that I’ve needed to “adapt” to this project’s needs. For libraries that can be used “as-is” I prefer to just link them.

  1. Hi Dimdim,
    Excellent project, thank you for sharing it!
    I am working now to draw my own version of 2 layers PCBs, with Xmos XU208 (for I2S of course, but also for I2C commands), and your project is a great source of inspiration.
    How did you managed the click noise between DSD tracks, only software mute or will you use relays?
    Thank you in advance.

    • Thank you for your kind words. 🙂
      I too am finishing up an XMOS design with the XUF208 as well as an AK4118 for s/pdif inputs, no I2C though. I have the uC for that.
      The AKM dac chips have well documented problems with pops when changing between pcm and dsd.. they (akm) recommend using a relay to mute the output before making changes in the signal formats. But I don’t really remember having problems switching between different DSD tracks. I’ll check to see if it’s something I missed. The dac is still in development mode, so I’m not really listening to it most of the time.

      • I have made a few XU208 and XUF208 boards using Amanero PCB size and pinout. The main reason was that Amanero requires different firmware for Windows and Linux (Daphile) and I want to avoid this situation. I have been tested them with a Chinese DAC based on AK4490, but the relay is not fast enough and sometimes I can hear a pop/click for a fraction of time before the relay acts.
        I finished a USB DAC project based on XMOS XHRA and dual AD1955 (controlled by a PIC uC) with I2S and SPI isolators, but the sound is better without isolators. Obviously it needs reclock and XMOS working as slave.
        The PCB I am working now is intended to be configurable, so if I will not succeed to make XMOS working as real slave, I will replace it with Amanero module, I will add STM32Duino board and I will move a few jumpers.
        Thank you and good luck!

        • Interesting that the relay turns out not being fast enough.. I have been worried that I would also have such a problem but I have not got there yet. Perhaps some solid state solution might be a better choice. I’ll look into it and keep you posted.
          Regarding the XMOS in slave mode, do you mean “real” slave mode, as in the dac generating the BCLK & LRCK signals and feeding them to the XMOS (along with MCLK) so that it only generates the DATA line, or just slaving the XMOS to the dac’s MCLK?

          • Just slaving the XMOS to the DAC’s MCLK.
            When I said “real” I was thinking about my last finished project. The clocks are located near the AD1955s, on the clean side, I2S isolator is 3in-1out version, so I force the XMOS to be a slave without programming the XMOS accordingly. As you know, XHRA is some kind of XU208, but factory limited to the “official” firmware. It was obviously from the beginning it will not sound well, but it was worth to try.

  2. hey, thanks, great work 🙂 Took a look at the code and it seems to be really well understandable. I like that a lot!

    Looking really forward to putting my dual ak4490 (china made board with XMOS U8) in this case: https://www.fein-hifi.de/images/product_images/original_images/256_0_rt935axb.jpg
    Not sure if I really reuse the VFD display since these are, electrically, a real pain to drive (basically they’re display tubes) or just put a SSD1306 0.98″ OLED there; but either way the tuner looks really nice in my Rotel stack 🙂

    By the way, what’s the code’s license? Public domain, GPL,…? I’m *considering* packing a lot of your AK4490/AK4118 stuff into separate libs to make it easier to reuse (and publish it on github under the same license, preferably GPL, and of course referencing you as the original author in each file).

    btw, this post is missing the ak4490 tag, that’s probably why I missed it and asked for it on part 1.

    • Crap, I missed this comment! Sorry..

      I haven’t really given much thought to a license for the code. AFAIK if I make no mention of a specific license it “defaults” to a very permissive license. So, for the time being, everyone is free to do whatever one wishes with my code. 🙂

      You’re right about the tag, I’ve fixed it..

      • Haha, no problem 😉 and thanks 🙂 I’ll post the link here once I tested the lib (which might take some time since I’m doing a lot of stuff in parallel in my spare time and I’m moving in with my gf ^^’)

    • I haven’t gone that deep into studying the 4497’s datasheet but I doubt it.. Many of the parts of the code will probably work, but the 4497 is not register-to-register compatible with the 4490.

  3. The more i read your blog the more I am intrigued to build your dual mono dac. I am bit novice on diy dacs but have soldering skills.

    How the dual dac compares (soundwise) to the single ak4997 diyinhk board?

  4. Pingback: Arduino controlled Dual Mono AK4490 DAC (Part 1) | Dimdim's Blog

  5. Hi Dimdim,

    Thx for Your work. I;ve bought tft board and i;m trying to get it works. I use stm32 and Yours librarry Adafruit_ILI9481_8bit_STM. I still got white screen. I;ve checked all wires, i;ve made a small test application to check if all pins of STM react for command on/off.
    Arduino 1.85, Your librrary 1.72. The readID() return xD3D3D3D3 instead of 9481. Bellow is diagnostic print:

    Display Power Mode: 0xA
    MADCTL Mode: 0xB
    Pixel Format: 0xC
    Image Format: 0xD
    Self Diagnostic: 0xF
    Device ID: 0xD3D3D3D3

    Any suggestion? Maybe it it’s bad TFT screen (out of order/dead).

    Best rgds

    Marek

    • It might be a bad LCD, but it also might be an LCD with a different controller. Does it look exactly like the one I have?

      I have come across a couple of seemingly identical LCDs that worked but displayed an inverted image.

  6. Pingback: Arduino controlled Dual Mono AK4490 DAC (Part 3) | Dimdim's Blog

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