Soekris dam1021 S/PDIF & USB Board

The Soekris DAM1021 directly supports two s/pdif inputs, a coaxial and an optical one. Soren has provided us with a simple schematic to build the necessary circuit:

SPDIF-receiver-schematic-dimdim_v1

You could very well build this circuit in a breadboard – after all, it is a pretty simple circuit – and you could power it by the DAM’s J2 header, but I opted to do something more elegant and convenient. I designed a circuit board that would accommodate:

  • One coaxial s/pdif input, galvanically isolated.
  • Two Toslink inputs.
  • A mux chip to switch between the Toslink inputs.
  • A 1.2V power supply for biasing the coax input.
  • A 3.3V power supply for the Toslink inputs and their mux.
  • A USB to RS-232 bridge circuit, to accommodate connecting the DAM to a computer for firmware updates and control.

2015-12-07 20.43.37 (Large)

This is the schematic:

dam1021-Input-&-USB-schematic

This is the board’s layout:

dam1021-Input-&-USB-layout

And this is the BoM:

Soekris DAM1021 s/pdif inputs board
PCB Part Value
C1 100n 0805
C2 100n 0805
C3 100n 0805
C4 10uF 1206
C5 10uF 1206
C6 10uF 1206
C7 10uF 1206
C8 100n 1206
C9 100n 0805
C10 22p 1206
C11 22p 1206
C12 100n 1206
C13 100n 1206
C14 100n 1206
C15 100n 1206
C16 100n 1206
C17 100n 1206
R1 330R 0805
R2 1K 1206
R3 10K 1206
R4 51K 1206
R5 27R 1206
R6 27R 1206
R7 1.5K 0805
R9 4.7K 0805
R10 4.7K 0805
L1 47uH 1206
L2 47uH 1206
L3 ferrite bead 1206
U1 ADP150AUJZ-3.3-R7
U2 ADP161AUJZ-R7
U3 7SB3257DTT1G
U4 PL-2303HX Rev. A (not D!) SSOP-28
U5 MAX3232 SO16
Y1 12MHz crystal
OX1 TORX147
OX2 TORX147
X1 Amphenol 112419 BNC RA PCB JACK 75 OHM-LO/BL
TR1 Murata DA101C

Download schematics & PCBs here: DAM1021 S/PDIF Inputs and USB board (448 downloads)

I used the old PL-2303HX IC (Rev. A, not Rev. D!) for the USB to serial bridge, since it was the only such chip I could get my hands on when I was designing the board. It is officially supported by most operating systems with the exception of Windows 8 & 10, where it will work, but you might need to do some manual work to install the drivers.

On Windows 8 & 10, the system will find and install drivers by itself, but these drivers will probably not work correctly. Should that happen, the new COM port will have a yellow exclamation mark (as seen on Device Manager). You should download and install these drivers:  PL2303 Prolific Driver Installer v1.30 (386 downloads) Then go to Device Manager, right click on the problematic COM port and select “Update Driver Software”. Then click “Browse my computer for driver software”, then “Let me pick from a list of device drivers on my computer”. You should see two drivers – one dated 2015 and one 2010. You should pick the one from 2010. That should get your COM port working.

Toslink source selection is by J2, by driving the middle pin HIGH or LOW. LOW means input 1 (OX1), HIGH means input 2 (OX2). You may use a SPDT switch or outside logic (Arduino etc.).

This is the pinout of the main connector (from left (pin 1) to right):

dam1021-Input-&-USB-layout-main-connector

Main Connector
Pin Function
1 3.3VDC auxilliary out
2 GND
3 Toslink Select Input 1 or 2
4 Toslink out (TTL)
5 S/PDIF out (+)
6 S/PDIF out (-)
7 Vcc (4-5,5VDC)

The Serial Port connector is simpler. From top to bottom we have: Serial Out, Serial In, GND

I also designed a set of “helper” boards:

Soekris_J3_plus

  • A board for the DAM’s J3 header, exposing its (currently) useful signals. I2S input is via U.FL sockets.
  • A board for the Amanero Combo384. It is very basic, all it does is expose its I2S output and its 3.3V output.
  • A board for DIYINHK’s XMOS-based non-isolated board. It is also basic, exposing its I2S output and its 3.3V power supply input.

The most useful one (at least for me) is the one for the J3 header.
dam1021-J3-pcb

These are its pinouts (pin numbers from left to right):

J3_PCB H1
Pin Function
1 GND
2 Toslink in (TTL)
3 S/PDIF in (+)
4 S/PDIF in (-)
5 3.3VDC auxilliary out
J3_PCB H2
Pin Function
1 FSEL_IN
2 ISO_GND
3 ISO_3.3VDC_IN
J3_PCB H3
Pin Function
1 ISO_3.3VDC_IN
2 ISO_GND
3 Serial_Out
4 Serial_In
J3_PCB H4
Pin Function
1 GND
2 DAM Power LED