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Wireless digital audio transmission.

piotr_go 45378 59

TL;DR

  • A wireless digital audio link uses Nordic Semiconductor NRF24L01 radios to stream compressed MP3 audio between an AT91SAM7S64 transmitter and an AT91SAM7S512 receiver.
  • The transmitter encodes system sound with LAME at 320kbps and exposes a PulseAudio output module, so desktop audio can be redirected to wireless speakers with adjustable buffering.
  • The link runs in the 2.4GHz band and the NRF24L01 provides about 400kbps with acknowledgment and error correction.
  • The receiver uses a Helix decoder and TDA1543 DAC, while the newer version switches to a CS4344 DAC and can measure supply voltage.
  • A micro-sized version based on a reprogrammed Logitech Unifying receiver reaches only 128kbps, but the larger setup works through walls with the right antenna arrangement.
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  • #31 8268183
    PO.
    Level 20  
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    Well, that's exactly what I'm aiming for, I just wanted to play with this cube, only with the availability and price so-so ... It's nice to know that he is at Kogitech's - somewhere else, in some easy-to-use modules?
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  • #32 8268207
    piotr_go
    DIY electronics designer  
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    I know where it is not :) , there is no A4TECH in similar micro receivers. They put something in there that I couldn't identify.
  • #33 8268238
    PO.
    Level 20  
    Posts: 527
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    piotr_go wrote:
    I know where it is not :) , there is no A4TECH in similar micro receivers. They put something in there that I couldn't identify.


    There are no old logitechs either, mx1000 etc. and in various older receivers for their mice and keyboards, I know because I was looking there some time ago ;) both in the smaller and bookshelf mounts. In general, it is rather new equipment.
  • #34 8269033
    wilkolaski
    Level 18  
    Posts: 508
    Rate: 16
    Okay, but how many of them do you need, i.e. you can not connect one or two capacitors?
  • #35 8269582
    piotr_go
    DIY electronics designer  
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    What are all those thrifty?
    I would make a single-sided PCB, 2 capacitors and then what? Something will not work and I will have to do it again, probably throwing out some of the elements.
    I have a rule of how many power pins (not counting the mass) I try to give to the capacitors. So far, there have been no problems with the devices.
    Besides, it's an audio device, what if I could hear "beats flying" in the speakers ?! :(
    There must be decent filtration.
  • #36 8270817
    wilkolaski
    Level 18  
    Posts: 508
    Rate: 16
    Man, we got it wrong.
    In no case do I blame you for the amount of them, I'm just curious why you gave them so many, i.e. what it gives.
    In short, my question is out of pure curiosity.
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  • #37 8270829
    piotr_go
    DIY electronics designer  
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    Less power disturbance.
  • #38 8272462
    piotr_go
    DIY electronics designer  
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    I was able to get the nRF24LU1 + to run at full speed :)
    I figured it out by accident.
    Instead of sending data to it with usb_bulk_write (), I loaded the usbserial driver and sent the data as if to a serial port.
  • #39 8279817
    wojtii77
    Level 14  
    Posts: 373
    Rate: 13
    piotr_go wrote:
    9m, I still did not check.
    I also checked whether it would break through 2 floors. When I set the antennas properly, it worked.


    From what I remember, an ordinary FM transmitter connected to a 12V car socket had a range of 50 m + 2 walls behind which the radio was set to the appropriate frequency.
  • #40 8279866
    Mat_91
    Level 25  
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    wojtii77 wrote:
    From what I remember, an ordinary FM transmitter connected to a 12V car socket had a range of 50 m + 2 walls behind which the radio was set to the appropriate frequency.
    But an ordinary FM transmitter works at a completely different frequency and with a different power.
    piotr_go wrote:

    I was able to get the nRF24LU1 + to run at full speed Smile
    I figured it out by accident.
    Instead of sending data to it with usb_bulk_write (), I loaded the usbserial driver and sent the data as if to a serial port.
    So full performance from a micro transmitter?;> How about the range of this small contraption?
  • #41 8281663
    piotr_go
    DIY electronics designer  
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    Full performance. Range - poorly, when you walk between it and the receiver, it cuts, you would have to give another antenna or somehow turn it by 90 degrees because then it cuts much less often.
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  • #42 8282459
    nusch
    Level 15  
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    What about logitech unifying can be done so as not to lose basic functions, i.e. to have a mouse, keyboard and sound, or has your program completely replaced the standard logitech?
  • #43 8282476
    piotr_go
    DIY electronics designer  
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    Completely, I think the logitech people were intelligent enough to protect their soft from being read. (I did not have the opportunity to check very much because I tested the programmer and I could delete something first)
  • #44 8286579
    irekr
    VIP Meritorious for electroda.pl  
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    Another question.
    Would you undertake a similar set but:
    1. In the 5 GHz band
    2. With signal input / output in AES EBU standard in layer 1 and 2 (448 kbs DSR5.1), and / or optional Spdif in classic stereo.
    3. In another licensed band.
    greetings
    irek
  • #45 8287168
    piotr_go
    DIY electronics designer  
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    Getting nRF in our beautiful country is almost a miracle, let alone something faster on a less popular band :(
    nRF was the fastest I found (370kbps checked by me).
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  • #46 8291213
    stgw
    Level 2  
    Posts: 3
    Hello, is there any software that supports the transmitter under Windows, or only under Linux?
  • #47 8291351
    piotr_go
    DIY electronics designer  
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    So far I have only written the output module for PulseAudio. I have no plans for Windows drivers.
    At first, I was thinking about emulating some standard audio device in the transmitter so that it could be used with any system. Unfortunately, the processor is a bit weak to encode MP3 :(
  • #48 8309115
    nairamk
    Level 12  
    Posts: 10
    And what is the time shift in audio reception?

    I won't believe he's gone.
    - sampling, compression to mpeg, transmission, decompression and playback.

    It must take a while ...

    Is it suitable for more than music?

    Why is he asking such a question?

    Because I once bought a Motorola A2DP set. The set consists of a small soap dish with audio inputs and a bluetooth module, and of course headphones.

    ... what was my disappointment when it turned out that the time shift of the audio signal completely EXCLUDES such a solution for watching movies. It's just annoying to see sooner that they are talking than the sound reaches your ears.

    As a result, the set is completely unused :(

    How is it with you?
  • #49 8310001
    piotr_go
    DIY electronics designer  
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    The transmission delay is, of course, but the latency in the PulseAudio output module is adjusted so that the image matches the sound. If anyone wanted, it can even be set so that the sound is ahead of the picture.
  • #50 8369847
    uzi18
    Level 24  
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    How Much Can I Pull Without Compression?
    Maybe some simple compression algorithm should be used.
  • #51 8370536
    piotr_go
    DIY electronics designer  
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    And MPEG is what if not lossy compression?
  • #53 8492900
    Anonymous
    Anonymous  
  • #54 8495332
    piotr_go
    DIY electronics designer  
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    2 channels from 5.1 to play on another device? Although I have never tried it, I think PulseAudio does. You would have to look in the manual.
    For a full 5.1 transmission, the receiver is too weak (and obviously - stereo DAC).
  • #55 8875159
    NDorian
    Level 1  
    Posts: 1
    to: piotr_go

    Hello. Saw your project is really cool!
    Can I ask you for a little help?
    I'm trying to do something similar, or even just run the radio transmission. There I have SAM7-EX256 with a module MOD-NRF24L which connects via UEXT to SPI0 (CS0). I am suffering for about a week, I can not configure the SPI to work with nRF24. Taken as a basis for several projects including "STM32-103STK" and "LPC-P2148 demo code. " I can not understand or I'm such a fool, and my hands are curves or something on the board.
    Could you show how to make the setting for SPI nRF24 on SAM7?

    my e-mail address:
    night.dorian @ gmail.com

    Thanks in advance!
  • #56 8875213
    piotr_go
    DIY electronics designer  
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    spi.c:
    [code:1:1f07950116]//SPI_MR bits
    #define PCS3 0x80000
    #define PCS2 0x40000
    #define PCS1 0x20000
    #define PCS0 0x10000
    #define LLB 0x00080
    #define MODFDIS 0x00010
    #define FDIV 0x00008
    #define PCSDEC 0x00004
    #define PS 0x00002
    #define MSTR 0x00001

    //SPI_CR bits
    #define LASTXFER 0x1000000
    #define SWRST 0x0000080
    #define SPIDIS 0x0000002
    #define SPIEN 0x0000001

    //SPI_CSRx bits
    #define DLYBCT 24
    #define DLYBS 16
    #define SCBR 8
    #define BITS 0x10
    #define CSAAT 0x8
    #define NCPHA 0x2
    #define CPOL 0x1

    //PIOA peripheral pins
    #define MISO 1
  • #57 10007637
    mpx-fm
    Level 19  
    Posts: 441
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    stgw wrote:
    Hello, is there any software that supports the transmitter under Windows, or only under Linux?



    is pulseaudio-0.9.6-1.win32.zip
    (911 KiB)     but you have to ask the author to let the author test - I don't have the equipment
    http://www.cendio.com/pulseaudio/

    you can also yes (I did not check) Link-Google Translate Link

    and so on: via http://sourceforge.net/projects/portableubuntu/
    Code: text Expand Select all Copy to clipboard
    Portable Ubuntu for Windows
Przenośne Ubuntu dla Windows jest sytemem Ubuntu działającym jak aplikacja Windows. System ten został zbudowany przy użyciu jądra Colinux, X serwera Xming, i serwera Pulseaudio dla Windows. Przenośne Ubuntu dla Windows jest przydatnym narzędziem, jeśli musisz przenieść się na stanowisko z komputerem na którym jest zainstalowany system Windows.
    Link
  • #58 10008786
    piotr_go
    DIY electronics designer  
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    Wish it were that simple...
    Unfortunately, PulseAudio has to be compiled with modifications yourself. For this you need to add the LAME library and probably some USB driver.
    This driver can be the biggest problem. Under Linux, you can bypass it and communicate directly with the endpoints of the device.
  • #59 10014750
    mpx-fm
    Level 19  
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    and it's not better to think about something cheaper than nrf2401 + AT91SAM, for example on STM32W108
    it would be cheaper several times
    I also saw prefabs from Chinoli. and from some Italian company Link Link

    or let me remember- hmmm ...
    I do not remember at the moment, but there is no new integrated scalak - 2.4GHz transceiver for audio transmission
    I will look for it in my free time, I only remember that its cost was close to nrf2401, as far as I remember, it was spdif and the analog could be sent with it
  • #60 10015508
    piotr_go
    DIY electronics designer  
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    STM32W108 is not suitable because it has:
    - too low transmission speed
    - too low core speed
    - not enough frame
    - no i2s
    and the transmitter is not suitable because there is no USB.

    A ready scalak (also from the Nordic company) is of course and was even at the time when I was designing this circuit, but I can't buy it.
    The NRF24L01 is quite popular for that. Even if you can not buy it, there are a lot of devices from which it can be disassembled.

    The project was to be an introduction to the construction of stereo headphones with a microphone.
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Topic summary

✨ The discussion revolves around a wireless digital audio transmission system utilizing Nordic Semiconductor's NRF24L01 module operating in the 2.4GHz band. The transmitter is based on the AT91SAM7S64 microcontroller, employing the LAME MP3 Encoder for audio compression at a bitrate of 320kbps. The system allows for audio redirection to wireless speakers via PulseAudio, with adjustable buffering delay. The receiver uses the AT91SAM7S512 microcontroller and the Helix decoder, with TDA1543 as the DAC. Users inquire about range, costs, potential production, and compatibility with existing devices, while the author shares insights on component sourcing, programming challenges, and latency management. The conversation also touches on alternatives like Bluetooth A2DP and the feasibility of using different microcontrollers for similar applications.
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FAQ

TL;DR: DIY 2.4 GHz audio link streams 320 kbps MP3 up to 9 m indoors; “The latency can be set freely” [Elektroda, piotr_go, post #8264643] Range and delay are user-tuneable via PulseAudio on Linux [Elektroda, piotr_go, post #8262996]

Why it matters: Makers can build low-cost wireless speakers that beat unstable Bluetooth A2DP in sound quality and control.

Quick Facts

• Link speed: ~400 kbps raw, 320 kbps payload using NRF24L01+ with ACK enabled [Elektroda, piotr_go, post #8262444] • Verified range: 9 m LOS; penetrates two floors with antenna alignment [Elektroda, piotr_go, post #8262996] • Receiver draw: ≈60 mA playing, 14 mA idle [Elektroda, piotr_go, post #8262444] • BOM cost: PLN 150–200 per Tx/Rx pair (≈€35–45) in small runs [Elektroda, piotr_go, post #8263100] • Tuneable channels: any 2 MHz slot between 2.400–2.5 GHz to dodge Wi-Fi [Elektroda, piotr_go, post #8263220]

What hardware makes this 2.4 GHz audio link work?

The transmitter uses an AT91SAM7S64 MCU driving an NRF24L01+ transceiver; audio is pre-encoded to 320 kbps MP3 on the PC. The receiver runs an AT91SAM7S512, decodes via the Helix MP3 library, and outputs through a TDA1543 or CS4344 DAC [Elektroda, piotr_go, post #8262444]

How far can the signal travel in real homes?

Open-space reach is about 9 m; with antennas aligned it played through two concrete floors. Mis-alignment or walking between devices can cause dropouts, especially with the micro-sized transmitter [Elektroda, piotr_go, #8262996; #8281663].

Will it clash with my 2.4 GHz Wi-Fi router?

You can program any 2 MHz channel inside 2.400–2.500 GHz, so selecting an idle slot avoids Wi-Fi overlap [Elektroda, piotr_go, post #8263220]

Is latency noticeable when watching movies?

No. PulseAudio lets you set buffer delay so audio matches video; users can even advance sound ahead of picture if desired [Elektroda, piotr_go, #8264643; #8310001].

What power supply do I need for the receiver?

Expect roughly 60 mA during playback and 14 mA while waiting for packets, so a 3.3 V source with ≥100 mA headroom is safe [Elektroda, piotr_go, post #8262444]

How much will a DIY set cost to build?

Prototype parts sourced from multiple vendors cost PLN 150–200 per pair. Bulk buying or PCB panelisation lowers the figure [Elektroda, piotr_go, #8263100; #8263180].

Can I etch a single-sided PCB to save money?

Not advised. Nordic’s layout guide calls for a solid ground plane and plenty of vias; single-layer boards hurt RF performance [Elektroda, piotr_go, post #8263270]

Why skip Bluetooth A2DP modules that cost only PLN 70?

The author reports frequent audio dropouts and lower SBC codec quality, whereas LAME-encoded MP3 remains stable at 320 kbps [Elektroda, piotr_go, post #8265434]

Is there Windows software, or only Linux support?

Only a custom PulseAudio output module for Linux exists. Porting to Windows would need recompiling PulseAudio with LAME and writing a USB endpoint driver [Elektroda, piotr_go, #8291351; #10008786].

Can the system transmit 5.1 surround sound?

No. The receiver’s MCU and stereo DAC limit throughput; PulseAudio can down-mix 5.1 to two channels, but full 5.1 exceeds processing and bandwidth limits [Elektroda, piotr_go, post #8495332]

What’s an edge-case failure I should plan for?

The micro-transmitter stutters when a person blocks the path because its PCB antenna lacks gain. Mounting a quarter-wave whip or rotating 90° reduces the issue [Elektroda, piotr_go, post #8281663]

How many decoupling capacitors are really necessary?

Place a 100 nF ceramic at every Vcc pin; this lowers supply ripple and prevents audible “beats” in audio output [Elektroda, piotr_go, post #8269582] "Less disturbance equals cleaner sound," notes the designer.

Does the NRF24L01+ support lossless audio if I skip MP3?

Practical payload is ~370 kbps after overhead. CD-quality stereo PCM needs 1.4 Mbps, so compression (MP3, AAC, or ADPCM) is mandatory unless you drop sample rate or channels [Elektroda, piotr_go, post #8369847]
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