Raspberry Pi Pico spdif_recorder

Overview

• Hi-Res recorder from S/PDIF input to WAV files on microSD card
• Bit resolution: 16bit or 24bit (2ch)
• Sampling frequency: 44.1 KHz, 48.0 KHz, 88.2 KHz, 96.0 KHz (, 176.4 KHz, 192 KHz)
• Recording only, no monitoring or playback functions

Supported Board and Peripheral Devices

• Raspberry Pi Pico or Raspberry Pi Pico W (rp2040)
• S/PDIF Coaxial or TOSLINK Rx module (DLR1160 or equivalent)
• microSD cards (recommend SD-XC, V30 cards)

Pin Assignment & Connection

S/PDIF Rx

Pico Pin #	GPIO	Function	Connection
20	GP15	DATA	from S/PDIF data

Note:

• For Coaxial input or switchable inputs between Coaxial and TOSLINK, refer to pico_spdif_rx

microSD card

Pico Pin #	Pin Name	Function	microSD Pin Name	microSD Pin #
4	GP2	SPI0_SCK	CLK	5
5	GP3	SPI0_TX	CMD	3
6	GP4	SPI0_RX	DAT0	7
7	GP5	SPI0_CSn	CD/DAT3	2
8	GND	GND	VSS	6
36	3V3(OUT)	3.3V	VDD	4

Note:

• As for the wire length between Pico and SD card, short wiring as possible is desired, otherwise errors such as Mount error and Write fail will occur.

Button/Switch (Optional)

Pico Pin #	GPIO	Function	Connection
9	GP6	Input	16bit/24bit switch
10	GP7	Input	Start/Stop button

How to build

• See "Getting started with Raspberry Pi Pico"
• Put "pico-sdk", "pico-examples" and "pico-extras" on the same level with this project folder.
• Set environmental variables for PICO_SDK_PATH, PICO_EXTRAS_PATH and PICO_EXAMPLES_PATH
• Confirmed with Pico SDK 1.5.1

> git clone -b 1.5.1 https://github.com/raspberrypi/pico-sdk.git
> cd pico-sdk
> git submodule update -i
> cd ..
> git clone -b sdk-1.5.1 https://github.com/raspberrypi/pico-examples.git
>
> git clone -b sdk-1.5.1 https://github.com/raspberrypi/pico-extras.git
> 
> git clone -b main https://github.com/elehobica/pico_spdif_recorder.git
> cd pico_spdif_recorder
> git submodule update -i
> cd ..

Windows

• Build is confirmed in Developer Command Prompt for VS 2022 and Visual Studio Code on Windows environment
• Confirmed with cmake-3.27.2-windows-x86_64 and gcc-arm-none-eabi-10.3-2021.10-win32
• Lanuch "Developer Command Prompt for VS 2022"

> cd pico_spdif_recorder
> mkdir build && cd build
> cmake -G "NMake Makefiles" ..
> nmake

Linux

• Build is confirmed in rp2040-dev-docker:1.5.1
• Confirmed with cmake-3.22.1 and arm-none-eabi-gcc (15:10.3-2021.07-4) 10.3.1

$ cd pico_spdif_recorder
$ mkdir build && cd build
$ cmake ..
$ make -j4

Upload

• Put "pico_spdif_recorder.uf2" on RPI-RP2 drive

Serial command interface

• Serial interface is available from USB port of Raspberry Pi Pico.

Key	Function
Space	Recording Start Standby / Recording Stop
r	Resolution change 16bit/24bit (default: 16bit)
s	Manual split
b	Auto blank split on/off (default: on)
v	Verbose for monitoring messages
c	Clear WAV file suffix to 1
w	Configure Wi-Fi (for Raspberry Pi Pico W only)
h	Help

Recording start/stop/split features

• Standby recording start while silence and auto start when sound detected
• Auto stop and standby restart when long blank detected
• Auto split of WAV file when short blank detected
• Manual immediate split of WAV file without gap

LED indicator

• Slow blink: Recording is on-going.
• Fast blink: Background file proceses to close previous file and prepare next file are on-going. During this term, no command requests can be accepted.
• Repeated Slow blink and Fast blink: indicating errors (see log on serial console.)

microSD card

Card recommendation for Hi-Res recording

• Due to the limitation of single bit SPI interface driven by Raspberry Pi Pico, even with highest class microSD cards (as of 2024), recording in 24bit 176.4 KHz or 192.0 KHz is challenging. It will sometimes causes the drops of audio sampling data. The bandwidth status can be monitored in Verbose mode.
• The most severe situation for bandwidth is to start suceeeding track recording when previous long-time track more than 20 minutes has to be closed.
• With following recommended microSD cards, recording in 24bit 96.0 KHz will be stable as far as experimentally confirmed.
• Format micorSD card in exFAT with official SD Card Formatter before usage.

#	Vendor	Product Name	Part Number	Comment
1	Samsung	PRO Plus 256GB	MB-MD256SA	24bit/192KHz is worth trying for non-long-time tracks. 24bit/96KHz is stable.
2	SanDisk	Extreme PRO 256GB	SDSQXCD-256G-GN6MA	24bit/192KHz is too challenging. 24bit/96KHz is stable.

File timestamp

• File timestamp is synchronized to NTP if using Raspberry Pi Pico W and connected to Wi-Fi.
• Otherwise, timestamp starts from 0:00 a.m. Jan. 1st, 2024 (UTC+0).
• exFAT format (thus, > 64GB SD-XC cards) is recommended to reflect timezone.
• In case of FAT32 format, timestamp cannot reflect timezone, therefore, it's always shown as UTC+0 time.

Card trouble shooting

• In case of card mount error or fundamental access errors, please confirm with FatFs test