tournedos wrote:

The "Ye Olde Format", as I now call it 😁, used by BG4004 and I guess 2404, has really nothing in common with Datalink, new or old. The only Beomaster using that format is 2400-2 as far as I understand. The message only contains a couple of bits, and as these Beograms don't even have a microcontroller, is decoded completely with hardwired discrete transistor logic at the Beogram end. I've never seen it documented, but it would be possible (although tedious and boring) to decipher from the Beogram schematic. Would be easier to scope it off the wire, but I only have the BG4004 and it isn't very talkative by itself 🙂

I've got the BM2000 (1983 version, model 2917 IIRC... (*flips over Beomaster... yap!*), which uses the v1 version of Datalink. So, if all goes well, I can use the codes which are mentioned in the MCL2 service manual for Tape1 (tape), Phono (Beogram), Tape2 (DTV/DVD/HTPC) or Tuner. And even then I have some spare addresses to play around with, since the protocol has space for expansion and the Beomaster should happily ignore anything that isn't meant for it.

I don't think it's patented, and that wouldn't prevent any personal use anyway. The state-transition diagrams have been published in that article, so they are public information as well - however, the actual article has copyrights so let's not regurgitate it here.

A DIY project, which would probably be only point-to-point communication, will manage with a much simpler implementation that doesn't  care about collision detection. That would mostly be an issue on an MCL bus with multiple devices, like a multiroom installation.

Beolink is essentially a single-wire CSMA/CD protocol which should be a piece of cake to implement in any recent microcontroller. Keep in mind, that current uC's run on clocks that are in the 4-20MHz range, which gives you plenty of cycles to do anything aside from generating or reacting on Beolink messages. It doesn't implement error correction, the only thing to do in case of a collision (parity error when reading the message back) is jam (pull the bus low for a set amount of time) and repeat the message.

I'm planning to do home automation, but I want to use Ethernet or DMX512 to control my lighting, as I don't want to burden the Beolink bus with anything I don't need. Although it would be awesome to get a 455KHz receiver, wire it up to the Beolink bus and control the entire system with a Beo4, my current implementation will use a server, web page and touchscreen PC or PDA like an iPod Touch. The Beosystem and all associated hardware will be slaved to the home automation network, not the other way round.

premiumverum wrote:

The Beogram 3000 tangential will datalink with your BM2000. I used to have one with my BM3000, which is nothing more then a remote controllable BM2000. It's a great and good looking turntable!

I'm more inclined to go for the black verison of the BG5500, as it looks a little more like the 'original' BG2000 than the BG3000 does.

At least I know now that it's possible to link products from the newer (late '80s, early '90s) series with the 1980's Jensen gear, maybe I'll even put a Beosound Ouverture in the bedroom! I already installed a spare CAT5 cable for multiroom audio when decorating my flat, it's currently got L/R audio only, but that also means I got two wire pairs left for Beolink and possibly DMX512.

Little update, for the people who would like to fiddle around with the Datalink/Beolink protocol: As the codes are the same as for the B&O remotes, sending and receiving Datalink codes is supported in the LIRC and WinLIRC (Linux Infrared Remote Control) packages!

The only thing you need are a base resistor (470ohms should be OK) and NPN (BC547/550) transistor for the transmitter circuit, the receiver circuit can be a passive wire to the LIRC input. I'll post detailed schematics later.

I would have loved to do more research, but I think there's no need to reinvent the wheel, right. 😕

Time to give this thread an update...

The (Win)LIRC trick only works for systems equipped with a remote from Beolink 1000 up, since that's the point B&O introduced a new, multiroom-capable, Datalink format as outlined in the MCL2 service manual. The LIRC codes are programmed from that or just trained from a remote.

The 'older' (I'll call it 'Type 1' from now on) Datalink format, as used by Beosystems 2000-5000 and later systems between the components, has a simpler frame structure and I'll outline it here.

Here's the setup I used for reverse engineering the format, it's easy when you have a digital storage oscilloscope with logging capability handy. I made a little gadget which allowed me to eavesdrop on the bus:

Basically, not much more than a 7-pin DIN plug I scrapped off an old Beocord and a scope probe. Next, I just started hammering some keys on the Beomaster and Beogram and log everything that was transmitted. With some careful examination, here's what I found out:

• Signals are transmitted as 8-bit codes, with the MSB being the first, and with MSB always 1. This allows the controllers inside the devices to synchronize with the transmitted signal, as they trigger on the falling edge. 7 bits (128 codes) are available for use, and I haven't seen any codes beneath 0xA0 (hexadecimal) in the Beosystem 2000.

• A full 8 bit transmission lasts for 25 ms (so the bit time is 3,125ms like in the new format), and a message is repeated after a 25ms space to ensure its validity.

• A logic 'one' is active low, and for the rest, it's more or less a standard serial transmission which you can implement in any microcontroller. In theory, a USART can do it (320 baud, 7 data bits, 0 stop bits, no parity), but building it in software is a lot easier.

Having collected some data, I started work on a transmitter in an AVR development board, and connected it to my Beosystem (here on the bench for some more convenient testing):

And the tedious work began, pummeling the Beosystem with random Datalink codes until I found out some useful effect. It wasn't long until I heard a loud, satisfying 'CLICK' from the Beomaster's standby relay -- Success! I have been able to figure out the majority of the Beomaster and Beocord codes (the Beogram still needs some work), and I can already control the whole system without even having to touch it. As far as the actual Datalink functionality goes, that is. 😕

Some remarks on the DL function (even some that might be surprising):

• Codes from a specific source (Tape, PH) only function when that source is selected. For example, if you hit STAND BY on a Beocord while the tuner or Phono is selected, only the Beocord will stand by, instead of the entire system.
• TAPE 2 can be selected from remote sources. The switch on the Beomaster's front panel is only a dumb selector which informs the controller.
• When recording from PH, a special code is sent to the Beomaster to prevent any intervention (and therefore a faulty recording). In this case, the front panel buttons are ignored.
• Most, if not all, functions of the Beocord can be operated from Datalink. This is probably because of the later Beomaster 3000, which can operate the tape (and phono) deck with the remote. Seek, pause, play and record are all accomodated in the Datalink codes, however, I haven't been able to figure out all Beogram codes yet (which will probably also feature seek forward/back, because of BG3000), since I need some additional test subject hardware for that. 🙂
• Volume control and muting are NOT operated from the link. This wouldn't be convenient in a multi-room system anyway, since sending, for example, a mute command on the bus would mute ALL connected receivers.
• STAND BY can be controlled individually for each device.

Hi Stoney3K, just wanted to thank you for posting your findings - only now had time to read them properly. Do you intend to publish the codes, or make me find them out myself? 😁

(I don't blame you if you want to keep them to yourself - nobody else publishes anything either, everybody just wants to sell you something, or at least reserve the possibility 😭  )

tournedos wrote:

Hi Stoney3K, just wanted to thank you for posting your findings - only now had time to read them properly. Do you intend to publish the codes, or make me find them out myself? 😁

(I don't blame you if you want to keep them to yourself - nobody else publishes anything either, everybody just wants to sell you something, or at least reserve the possibility 😭  )

I'll post them here (at least the Beosystem 2000 codes from my own set) once I'm 100% positive that I found every code in the book and I know which code does what. If you're really in a hurry, you can always brute-force them yourself, since there are only 128 possible codes... that's exactly what I've been doing anyway. 🙂

If I'm selling stuff, it's only hardware which works with Datalink. Either a monitoring or injection gadget (so you can connect a central server to it for home automation) or something more intelligent like a Datalink device switching unit for Beomasters and Beosounds that may be a few AUX sockets short. 😕

The protocol is not rocket science and in principle, it's proprietary, so I'd be stupid if I would claim codes as my own.

No hurry at all, my current projects (which are on hold anyway) are on the infrared side, which is much more complex. I just think that compiling a comprehensive list of commands will need some cooperation, as nobody will have every possible device to try out in practise. They may have different semantics even though the commands are the same.

How is the development of the datalink device going?

I think I need one in order to be able to turn on my bedroom mounted BM4500 from a Logitech Duet that I would like to use as an wakeup alarm.  The BM4500 is connected to an MX5500 via an AUX cable and my intention was to use either the unused TAPE or CD inputs for the Duet.  The device would need to detect an audio line level signal emitted by the Duet and use this to trigger the transmission of the correct code to wake the B&O.

Does anyone have a suitable circuit for generating a trigger (5v ?) from an audio line level signal?

Richard

Nothing new from this side... but the trigger circuit would be a high gain amp (one or two transistors, or an opamp), couple of rectifying diodes and an RC filter. Using a suitable microcontroller with an A/D converter, you could do it all in software.

tournedos wrote:

Nothing new from this side... but the trigger circuit would be a high gain amp (one or two transistors, or an opamp), couple of rectifying diodes and an RC filter. Using a suitable microcontroller with an A/D converter, you could do it all in software.

Are you saying that it can be done with just a suitable microcontroller with an A/D converter, a single device?  Its been 25 years since I designed anything from scratch so do you have suggestions of a suitable device / circuit.  Would I need to buy the development platform for the microcontroller too?

One thing I have noticed tonight whilst playing is that both TV (V.OPT 2) and BM4500 (A.OPT 0) turn on if I press CD or TAPE on the BL1000 but only the BM4500 turns on if I press CD or TAPE on the BM4500.  I presume the same would happen if I was to trigger via datalink so could/should a developed device transmit IR codes like the BL1000?

I am surprised something like this does not already exist...

Many microcontrollers have a (slow serial approximation) A/D converter that has 10 bit resolution, so using the full 5V reference would give about 5V / 1024 = 5 mV resolution -> just bias the A/D input with two resistors, connect the audio there through a series cap, and follow the reading. -20 dB from the full audio swing (1 Vp-p) should still show as couple of bits worth of signal after the conversion, therefore no problem telling real music content from silence.

AVR controller family was already mentioned, and I can also recommend them as straightforward powerful chips, nowhere near as quirky as PICs for example. If you have any idea about C programming (or are willing to learn), check out