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:
Rev.-1.2-pic
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:
USI-parts-placement-rev1.2

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.

Update: TFT HiFiDuino v2.13

I did a little work on the TFT HiFiDuino code, incorporating most of the enhancements I made to the ArDAM1021 code.

v2.13_1

v2.13_4

v2.13_2

v2.13_5

v2.13_3

v2.13_6

These are the enhancements:

  • Option of displaying white text & graphics on black background as well as the “original” look.
  • New encoder code (it requires a new library).

Plus a few minor bugfixes here and there.

The new version of the code is here (v2.13): TFT_HiFiDuino_v2.xx (1176 downloads) (Note: As always, the code on this page may not be the current one, i.e. there may be a newer version available. The latest version is always up at the project’s official page.)

I will also update the code’s official page with the new version of the code.

TFT HiFiDuino v2.01 + video

As is usually the case, a few bugs crept into the v2 release. So, here is v2.01: TFT_HiFiDuino_v2.xx (1176 downloads) (Note: As always, the code on this page may not be the current one, i.e. there may be a newer version available. The latest version is always up at the project’s official page.)

Also, here is a video of the code in action:

TFT HiFiDuino v2!

It’s official: Version 2 of the TFT HiFiDuino controller is complete!

There is a number of changes, thus the new version:

  • New minimal display mode as default. Goes into full display when changes are to be made to parameters.
  • Full graphics support in the minimal display.
  • New proportional fonts (TrueType).
  • New IR code. Now supports a much larger range of remote manufacturers.
  • Support of MCP23008 IC to control misc devices.
  • New option to set 0db as default (power-on) volume for connection to a preamp.

The code is (and will remain) compatible with my current shield. (Hint: shield v2 is also coming up!)

New requirements:

Plus the good old UTFT library.

I am including the necessary fonts and bitmaps in the ZIP. The fonts should go into your UTFT & UTFT_DLB directories, usually found in the Windows user’s Documents folders (for example, here: c:\Users\<user name>\Documents\Arduino\libraries\UTFT_DLB\).

The bitmaps should go into your sketch’s folder.

I have included in several places in the code SerialUSB output for debugging purposes. It is commented out in this release for performance purposes. However, it is very easy to re-enable for either debugging or viewing of the IR codes sent to the Arduino. You may use these IR codes to customize the code to support your remote by changing the relevant #define statements in the Remote control definitions section.

Due to code size and performance requirements I’m afraid that from v2 onwards TFT HiFiDuino will only be compatible with the Arduino Due. Sorry, it’s the price to pay for nice graphics. Thankfully, it’s a pretty low price. 😛

You may download it here: TFT_HiFiDuino_v2.xx (1176 downloads) (Note: As always, the code on this page may not be the current one, i.e. there may be a newer version available. The latest version is always up at the project’s official page.)

I will soon update the code’s official page to v2.

IMG_8600_resize

The Raspberry Pi: Audio out through I2S

There are currently four ways to get audio out of the RPi:

  1. Use the audio out 3.5mm jack. It’s very easy to get it to work, but the sound quality is pretty bad, since it uses PWM to generate the sound. Due to that, its real resolution is in the neighbourhood of 11 bits. We have no use for that.
  2. Use the HDMI port. It works OK, but is useless to us audiophiles.
  3. Use a USB to I2S adapter, such as an Amanero or an XMOS-based device. Now we’re talking. They work quite well, and the quality of the I2S signal is dependent largely on the technology used (CPLD vs. XMOS, etc) as well as the quality of the on-board clocks. The problem is that they add another link to the audio chain, as well as increase the cost. Remember, the RPi is supposed to be a low cost solution.
  4. Use the GPIO pins of the RPi to get direct I2S output. This sounds way more interesting, right? Let’s try that!

According to several sources on the Net, this is the pin out:

Raspberry_Pi_B_Plus_I2S_out

You will probably notice that the RPi does not support MCLK output. This means in practice that your DAC will need to have its own on-board clock (or internal PLL / oscillator or whatever). We can live with that.

Luckily, my Buffalo III has its own clock (of course it does!) and thus can be connected quite easily. Let’s try that:

IMG_8297_resize

Now we have to configure the software for I2S output. For my distribution of choice, Archphile, it’s a piece of cake: http://archphile.org/howto/i2s-dacs-and-the-raspberry-pi/

Audio playback works just fine!

Well, almost fine..

You see, in theory the RPi has a bit of a problem with its I2S output. Since the only clock onboard the RPi is a 19.2MHz crystal, it should have trouble generating proper clocks for its I2S output. For example, for 44.1KHz audio, the LR Clock must be running at precisely 44.1KHz. That is not possible, since the frequency is not a multiple of 19.2MHz. Thus, the frequency can be either 19.200.000 / 435 = 44.138KHz or 19.200.000 / 436 = 44.0366KHz. This is a limitation of the Broadcom BCM2835 in conjunction with the 19.2MHz crystal and there is nothing that can be done.

In order to confirm the theory, I decided to run a few tests. I hooked up my logic analyzer to my RPi, set it up for I2S output, and fed it some 44.1KHz music.

IMG_8453_crop_resize

I took 1 sec worth of samples with my logic analyzer, configuring it for I2S signal. I got this:

logic analyzer 4

The PCM Clock is already appearing a little dodgy. Let’s zoom in:

logic analyzer 5

logic analyzer 6

As you can see, the pulses do not have the same duration. They appear to alternate between two values. So it is obvious that the signal has jitter. A lot of jitter. Since we’re here, let’s have a look at the LR Clock signal as well:

logic analyzer 7

logic analyzer 8

The duration of the pulses appears to alternate between 11.33μS and 11.38μS, giving respectively 44.12KHz and 44.04KHz, values very close to the ones I calculated previously.

So, the theory is sound and the RPi’s clock is not up to snuff by strict standards. What this means is that the RPi’s I2S output is not capable of “Hi End” audio transmission. It is essentially not bit perfect (edit: this is not correct, strictly speaking. It is in fact bit perfect, it is just not “proper”.).

In the real world, chances are that this problematic clocking will not be particularly audible under normal circumstances, say with a normal-specc’ed sound system. But an audiophile should definitely steer clear of the RPi’s I2S output, instead opting for a USB to I2S interface.

The Raspberry Pi: Low cost music streamer

Enter the Raspberry Pi B+:

Raspberry Pi B+

It features:

  • A Broadcom BCM2835 SoC processor running at 700MHz
  • 512MB of RAM
  • A Micro SD slot for storage
  • A 10/100Mbps Ethernet port
  • 4 x USB2.0 ports
  • An HDMI output port
  • An analog audio / composite video output port
  • A 40-pin expansion header, exposing 26 x GPIO ports
  • A camera and a display interface port

Somehow they have managed to cram all that in an almost credit-card sized PCB.

And it costs less than 40€.

It runs Linux (of course..). There is a large number of general-purpose distributions available, as well as a few custom built ones. One of them is Openelec (an XBMC Media Center distro), another one is Volumio (an audiophile music player), a third one is SqueezePlug (it emulates a number of Media Servers, like Logitech Media Server, MediaTomb, MiniDLNA, etc. It also works as a Squeezebox (client)), etc.

So far, my favorite distribution is Archphile, an audiophile linux distribution. It may not have the polished look of Volumio or play 1080p video like Openelec, but is plays music wonderfully through a USB port (or through I2S if you are more of a DIYer).

So, what am I doing with it? I wanted to put a music streamer in my kitchen. I already have two Squeezeboxes in other rooms, so for the kitchen I thought I would try something more interesting.

But along the way, I discovered that it is a lot more useful than that. A very useful (and very rare) feature it has is the ability to bitstream DSD audio (a.k.a. SACDs):

RPi outputting DSD to Buffalo DAC

Raspberry Pi B+ outputting DSD to my Buffalo DAC

So now I’m considering adding an RPi network music transport to my main system.

Buffalo Shield revision for B3SE

As I said, I will release a new revision of the Buffalo shield that will have better support for the B3SE.

Since that will probably take some time, in the meanwhile, this is what B3SE (or 32s or II) owners should do to their shields in order to support the B3SE:

IMG_6908_res_mod

The idea is to connect the photosensor side of one of the optoisolators directly to the IP_S header on the B3SE. In order to do that, you will have to cut one trace on the PCB and solder directly onto one of the optoisolator’s pins. That’s pretty much it.

On the new revision of the shield there will be a jumper where you have to cut the trace plus an extra pin so that you don’t have to solder onto the isolator’s pin.

TFT HiFiDuino v1.06

Here is version 1.06 of the code: TFT_HiFiDuino_v1.06b.zip (570 downloads)
(11/12/2013: Update to v1.06b. Reason: minor bugfix)  (Note: As always, the code on this page may not be the current one, i.e. there may be a newer version available. The latest version is always up at the project’s official page.)

IMG_6903_fix_&_crop_res

IMG_6905_crop_res

The main difference is the support of Buffalo 3SE as well as an “always on” feature that bypasses the remote on/off sections of the code.

Here is the official change log:

– Compatible with Buffalo 3 and Buffalo 3 SE. Just comment out the relevant statement.
– Fixed “OS Filt” & “SR disp”.. They were not working correctly.
– Blue select boxes are gone.. they looked quite bad.
– Some other minor (mainly aesthetic) fixes..

A new revision of the shield is to follow (for improved B3SE compatibility).

Buffalo Shield v.1.1 for TFT HiFiDuino

Following my previous post on TFT HiFiDuino v.1.00, this is what you need to know in order to build my Buffalo Shield.

First of all, here are the DipTrace files (schematic & PCB): Buffalo Shield v.1.1 for TFT HiFiDuino (schematic & PCB) (1080 downloads)

And here is the relevant build & wire guide: Buffalo Shield v.1.1g for TFT HiFiDuino (documentation) (1271 downloads)

This is what DipTrace thinks the board ought to look like:
Arduino_Shield_1.1_Render_07_c

And this is what it actually looks like:
Arduino_Shield_v.1.1_1_800x872

Close enough..

This shield features:
– Galvanic isolation for the I2C signals as well as 2 digital outputs (Arduino -> Buffalo) and 1 digital input (Buffalo -> Arduino).
– EEPROM chip (24LC256) either in SMT or DIP footprint.
– Backlight control for the TFT through a PWM-controlled transistor.
– Headers for two rotary encoders.
– Output for power relay (for remote on/off).
– Header for IR receiver.

This is the schematic for the shield:
Arduino_Shield_Schematic-0.91

And this is the resulting PCB:
Arduino_Shield_PCB_v1.1b

This is a description of the various headers:

IR: Use a standard 38KHz IR Receiver Module, like the TSOP4838.
1: Signal (Pin 9)
2: GND
3: 3.3V

RotaryEncoder1: Use any simple rotary encoder.
1: Left pin (Pin 7)
2: Right pin (Pin 6)
3: Selector pin 1 (Pin 5)
4: Middle Pin & Selector pin 2 (GND)

RotaryEncoder2: Use any simple rotary encoder.
1: Left pin (Pin A3)
2: Right pin (Pin A4)
3: Selector pin 1 (Pin A3)
4: Middle Pin & Selector pin 2 (GND)

I2C_In:
1: SDA
2: SCL
(note: this is the I2C connection to the Arduino. SDA should be connected to pin 20 and SCL to pin 21)

I2C_Bypass:
1: GND
2: SDA
3: SCL
(use this if / when an isolator IC (U2) is not used to send the I2C signal to the Buffalo)

Isolated_Outs:
1: Out 1 (Pin A2)
2: Out 2 (Pin A7)

TFT_power:
1: TFT Backlight LED (dimmed by Pin 8)
2, 3: 3.3V (for TFT power & pin RD)
4: GND

PowerInput:
1: GND
2: Vin (8V-12V)
(connect here the power supply to the Arduino)

PowerRelay:
1: GND
2: 3.3V out (Pin A0) in case of Due, 5V in case of MEGA
(connect here the power relay that powers on the DAC)

To_Buffalo:
1: Buffalo Vcc (3.3V)
2: SDA
3: Sidecar Control (Pin 3)
4: Lock LED input (Pin A1)
5: SCL
6: Buffalo GND

TFT HiFiDuino: Phase 1 complete!

It took quite a bit longer than I had expected but I am happy to report that Phase 1 of the TFT HiFiDuino project is complete.

v.1.00_screenshot_1_800x471

The objectives of Phase 1 were the following:
– Have full control over the parameters of the ES9018 chip. Essentially be able to write to all of the useful registers.
– Be able to have full IR remote control functionality.
– Be compatible with both the MEGA as well as the Due Arduino boards.
– Be able to switch between all 8 of the supported s/pdif inputs, as well as between I2S sources (USB in my case).
– Develop an Arduino shield that would simplify the wiring of the thing as much as possible as well as provide galvanic isolation between the Arduino and the DAC board.

All of these objectives have been accomplished, so here is v.1.00 of the code: TFT HiFiDuino v.1.00 (452 downloads) (Update: there is a new version available! Click here for the latest version.)

If you happen to come across a bug, please let me know by posting a comment below.
Feel free to use it whichever way you see fit, modify it, redistribute it, whatever, as long as you do not profit from it.

Requirements:
UTFT Library
– Fonts (included in the ZIP)

I will also make available the schematics & PCB for the shield, although it is not really necessary for operation of the controller.
Here is a preview:
Arduino_Shield_v.1.1_1_800x872

Arduino_Shield_v.1.1_2_800x630