TFT HiFiDUINO Pro page is up..

Over 6.500 lines of code, completely re-written from scratch, it supports the ES9038Pro and ES9028Pro DAC chips.

Now supports both 3.2″ (legacy) and SainSmart 4.3″ TFTs.

Get all the juicy details:

New page: S/PDIF receiver with the WM8805

It took me a little longer than usual (the board had been sitting around in my workshop for almost a year and a half), but it’s finally up. A page for a very good quality and very versatile Arduino controlled s/pdif receiver.

Check it out here:

Controlling an AK4490 DAC with an Arduino

These days I’m co-developing an AK4490 based DAC. The aim is to end up with a no-compromise dual mono design, one that would perform at the very least on par with my Buffalo III.

Of course, to do that one has to run the 4490s in software mode.

As a matter of fact, it is generally preferred to run a 4490 in software versus hardware mode, for several reasons.

To begin with, in software mode the 4490 supports DSD decoding. It goes as far as to support a “Volume Bypass” feature which bypasses most of the processing done on the DSD signal (a.k.a. “the ΔΣ modulator”), resulting in more pure sound. But of course we do lose the ability to do volume control in software.

Software mode also allows us to try out all of the supported SQ features, like the different “Sound Setting” modes.

At last but not least, we get digital hardware volume control.

This is the prototype that we designed, getting I2S input from an Amanero and being controlled by my custom STM32 controller (more on that in the near future).

I searched the Net for any ready-made code that would control the 4490, but I couldn’t find anything worthwhile, so I began virtually from scratch.

So, my Arduino code (a.k.a. “aKduino”) enables:

  • Controlling an AK4490 through the I2C bus.
  • Automatic switching between PCM and DSD. It does rely on getting a “DSD type signal” from our USB-to-I2S interface of choice. The 4490 by itself is not capable of determining whether its input is PCM or DSD.
  • Setting the volume (in 9 steps.. just to confirm that volume control does indeed work).
  • Selecting “Volume Bypass” for direct DSD processing.
  • Selecting the internal DSD filter’s cutoff frequency (50KHz or 150KHz).
  • Selecting one of the 4 available PCM filters.
  • Enabling or disabling the Super Slow filter.
  • Selecting one of the 3 available “Sound Quality” settings.
  • Displaying all of the registers’ settings (for troubleshooting purposes).

Software Requirements:

  • Nothing (for now)

Basic Hardware Requirements:

  • Any Arduino (*)

(*) I should note here that the AK4490’s datasheet states that all of its I/O pins are expecting 3.3V logic levels but there has been a large number of reported cases of 5V Arduinos working without problems. I’m too much of a coward to try that myself so I used level converters for my initial testing and eventually a custom STM32 board that uses 3.3V logic but you may want to try your luck with 5V logic levels. Just don’t blame me if your 4490 gets damaged in the process.

Currently the code is at v1.35: aKduino Code (793 downloads)

Here is the revision history:

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.

Universal Signal Isolator Shield: Rev. 1.2

Since there has been a lot of interest in my Isolator shield these past few months, I have been optimizing its design.

The result of this optimization is this PCB:
It’s called “the Rev. 1.2”.

Nothing major has changed. The pinouts are still the same, the major components are the same, the functionality is essentially the same.

The changes are as follows:

  • New SPI header. It just passes through the SPI signals, nothing more. It does not connect to anything on the board.
  • New SPI_CS header. Useful only if / when connecting SPI peripherals.
  • Reset button. Because you never know..
  • New circuitry for the POWER_RELAY header. It now uses a MOSFET and it includes a diode for the reverse current coming back from the relay’s coil.
  • Decoupling cap for the IR receiver. Not absolutely necessary, but good to have.
  • More decoupling for the DC_UNR input.
  • Ground planes. Lower Arduino noise, at least in theory.

Here is the updated parts placement:

And this is the updated BoM:

USI Bill of Materials, Rev. 1.2
PCB Part Value Notes
U1 24LC256 SO-08 EEPROM chip
U2 Si8605 SOIC-16 I2C Isolator
U3 MCP23008 SO-18W 8 input/output port expander
U4 Si8642 QSOP-16 Serial port isolator
U5 ADUM1250 SOIC-8 I2C Isolator
Q1 BC856, BC808 or other equivalent PNP SOT-23 TFT backlight control
Q2 BC856, BC808 or other equivalent PNP SOT-23 port expander transistor
Q3 BC856, BC808 or other equivalent PNP SOT-23 port expander transistor
Q4 BC856, BC808 or other equivalent PNP SOT-23 port expander transistor
Q5 AO3400 or other equivalent N-Channel MOSFET SOT-23 power relay mosfet
B1 Bridge rectifier 1A DB107 DIP-4
C1 1000uF 16V
C2 100n 1206
C3 100n 1206
C4 100n 1206
C5 100n 1206
C6 100n 1206
C7 100n 1206
C8 100n 0805
C9 100n 0805
C10 100n 1206
C11 100n 1206
R1 8.2K 1206
R2 2K 1206 pull-up resistor (optional)
R3 2K 1206 pull-up resistor (optional)
R4 5.1K 1206
R5 5.1K 1206
R6 5.1K 1206
R7 2K 0805 pull-up resistor (optional)
R8 2K 0805 pull-up resistor (optional)
R9 8.2K 1206
R10 10K 1206
D1 1N9001 DO214BA
L1 Ferrite Bead, low DC resistance, 3216
L2 Ferrite Bead, low DC resistance, 3216
Reset PCB-mount momentary switch

Soon I will update the shield’s page with the new info.

New page: Universal Signal Isolator shield for the Arduino DUE

My Universal Signal Isolator shield now has its own page, complete with the board’s schematic and PCB.


I have tried to document the shield as best I could but feel free to comment if you see something that is not clear or is missing.

They’re here!

I’m talking about my new Universal Signal Isolator PCBs:

USI_bare_slanted USIs_bunch


I built one to test it out and everything seems to be working as it should. Next step is a page for the project, with schematics, a BoM and build instructions.

It is compatible with the current versions of both the ArDAM1021 and TFT HiFiDuino projects.

For now you can find more info in this post.


Universal Signal Isolator shield for Arduino DUE & MEGA

A few years back I designed a little Arduino shield who’s main function was to provide electrical isolation between an Arduino and a DAC (specifically a TPA Buffalo III).

The years have passed and my needs have changed with the introduction of the dam1021 DAC and its serial interface. My first though was to design a new shield specific to the dam but then I said “why not design a universal isolator shield?”. It would provide electrical isolation for both I2C as well as serial signalling.

Thus was born the Universal Signal Isolator shield for Arduino DUE & MEGA:


OK, it does look a lot more complicated than my first shield but remember, you only need to solder in the parts that your DAC actually needs.

So, what does this thing do?

1) Electrical isolation of I2C signals, complete with support of 8 isolated inputs or outputs (via an MCP23008 IC). Three of the MCP’s pins are high current outputs (up to 100mA).

2) Electrical isolation of up to 2 serial ports (implemented with an Si8642).

3) Electrical isolation of the second I2C interface of the DUE (implemented with an ADUM1250).

4) Powered either by 5VDC, 8-15VDC (non-regulated) or 7-12VAC (includes support for on-board rectification and filtering).

5) Support of a 5VDC power relay (up to 100mA).

6) Header for connecting a Nextion display.

7) On-board EEPROM memory (24LC256).

8) And of course full compatibility with the previous shield (same pinouts for the encoders, IR, TFT, etc.).

I will release the Eagle files once I have confirmed that the shield works as expected (I’m waiting for the first (and hopefully last) batch of PCBs).