I'm working on a project to get a beovision control my xbox media center. I have it half-way finished. If i connect my microcontroller to the datalink port of my beocenter 9300 i can make it interpret the signals relayed from my beo4. I also have the microcontroller emulating the ir-reciever on the xbox making it able to navigate the menus. In theory I should be able to control the xbox by linking these two modules together.

BUT: I want to use the datalink from the scart-port on my beovision, not from the beocenter. This is where my problem begins.

How do i separate the datalink-signal from the switch-signal? Is there a quick and dirty (or quick and elegant ) way to do this? I'm learning as i go here, so any advice is appreciated.

A quick and elegant way could be to connect a Lintronic -238 box to the SCART connection. Connect PIN 8 to IR data input of the -238 box, ground PIN 21 to ground IR input. This should work also from linkrooms. You will find Xbox IR codes in the Lintronic database.

see www.lintronic.dk 

Stefan 

stefan:

A quick and elegant way could be to connect a Lintronic -238 box to the SCART connection. Connect PIN 8 to IR data input of the -238 box, ground PIN 21 to ground IR input.

Extrapolating from that, I guess the data is just superimposed on the switching signal at a small amplitude. Connect a small cap to it and lead that to a op-amp stage biased to 2.5V (or half of what ever your microprocessor uses as its input levels), select the amplification correctly so that it will clip, and you should have a nice 5Vp-p bit stream. Be prepared for missing / extra leading and trailing edges because of the AC coupling. If the original signal levels are a volt or so p-p, even a single 74HC14 schmitt-trigger gate might detect it (after the cap and 2.5V biasing, that is).

Disclaimer: I have absolutely no knowledge on how Datalink is carried on the SCART - might even be modulated somehow - so I could be talking out of my a** and can't really advice you any more specifically.
 

Thank you for your reply, Stefan, but I'm trying to make this work without buying extra equipment. I would rather solve this problem by throwing free microcontrollers from my university on it. [:-)]

 

Does anyone know anything about how the datalink-signal is transmitted over pin8 when this same pin also carry the signal telling the TV which format it should display? I just need to filter out the pulses and put it into a format the microcontroller can understand. 

Mika:

THIS is exactly what i need. I think the data is as you say superimposed at a small amplitude, and i think your solution will work perfectly. I will try it tomorrow. Thank you very much! 

Let us know what you found out then. I might have the same project in my hands later on!

Edit: After a brief moment of brightness, I realized I could take a look in the MX/LX service manual that is on the site. On the spec pages, the data leves are actually described. If I understand them correctly, the data is indeed superimposed at a level of little more than a volt. You might get away with just the cap, two resistors and a 74HC14 (or any other kind of schmitt trigger / amplifier you can concoct with the spare components you already might have in your circuit).

Funny, the sets have a 8032 micro. I used to know everything about it!

SUCCESS! Well, kind of, anyway. Just got the controls working via my BC9300. Haven´t got access to my beovision right now, so i can´t test with that one just yet.

Is there a chance you would draw up a quick schematic for me to make sure i understand it correctly? I´m not familiar with the usage of opamps and buffers.

magnushj:

Is there a chance you would draw up a quick schematic for me to make sure i understand it correctly?

Will do, but it will take until tomorrow because I can't be bothered to use Corel Draw  

Super! Won´t be able to test until monday anyway! :)

The solution with 74hc14 would've been simple and elegant, but I took a look at the data sheet and it has a worst case hysteresis of over 1.5 volts (at 5V supply), so it would not be reliable. This could be implemented also with two or maybe one transistors, but since I know you digital people hate them, I reverted to the opamp circuit Here's a quick sketch done with my favourite CAD program...

The op-amp is connected as a comparator, with a reference voltage of about 2.75 volts (created by the divider R3/R4) and the datalink input is biased to 2.5 volts (by R1/R2). Any pulses arriving through C1 will trip the comparator (this is an inverting circuit, but you can probably invert the data in software just as well). The time constant of C1/R1/R2 should be about 10 ms, or less than 10 Datalink pulse widths, so the output after the comparator should be quite clean without stretching or shortening any pulses. When the Datalink input is "quiet" or low, the 2.75V reference ensures that the comparator will not be tripping by itself. R5 adds a 0.something volt hysteresis just to make sure that any interference won't result in spurious pulses (you should be prepared for them, or missing message start edges, in your software anyway).

LM324 was just the first suitable op-amp that popped into my mind. It's dirt cheap and should be readily available, but you can use any other op-amp as long as it will work with (less than) 5 volt single supply.

I'm pretty sure that this works, but can't guarantee it. You might have to tweak the values of C1 and maybe also the ratio R3/R4. R5 might not be needed at all. If you have an oscilloscope, tuning the component values should be a breeze. Good luck and let me know what happened, I'll need a similar circuit to connect my VDR to my tv (when I manage to get a Beovision, that is...)  

tournedos:

Here's a quick sketch done with my favourite CAD program...

 

 

Thank you very very much, mika, I'll keep you posted! I'm going to visit my parents this weekend to pick up my avant and maybe my mx7000, as an avant may be a bit difficult to drag to and from the electronics lab. (I'm also getting a BC9500 that needs some work, but that's another story.)

 

I tried your circuit last week, mika. I do get some pulses out, but they are not the same as the ones going in. Worked pretty good in the simulator in Electronic Workbench though! :)

Will try changing some of the components later today, didn't have the time last time.

Hi together,

very interesting topic!

But why do you use a capacitor before the op-amp? I would recommend to use a simple voltage divider by using 2 resistors because the datalink signal is level-dependent and not edge-dependent. The capacitor adds a differentiating function to the circuit that may be disturbing.

Hi Hagen!

What makes the solution with the capacitor so elegant to me is that I don't have to cut any of the original wires. I just solder a wire to the AVIO-port on the xbox and out comes the pulses. (In theory....) The pulses are actually being transfered through the cap and they look good, but I need to find exactly the right reference voltage for it to work.

If I were to use a voltage divider i would have to have a box containing the resistors, microchip, wires and make a mess outside the xbox.

I have found a temporary solution until I (hopefully) perfect mika's circuit, and that is by cutting the wire giving the format signal from the xbox, leaving pin 8 from the scart to give a nice 3-4vpp pulse which the microchip can interpret out of the box. The scart cable I use (Xbox advanced AV cable) has a box on it containing a small PCB and a Toslink port for digital sound. It was here i cut the wires and connected the wire to the microchip. This wire is then extended from the box on the scart cable to the inside of the xbox through a small hole in the chassis. It is not possible to do the same inside the xbox due to the multilayered mainboard.

This is an ugly temporary solution, but I need it to work so that I can focus on testing the software.  I found out yesterday evening that the controller just stopped working after some time in use. The code probably needs some clean up!
 

The voltage divider would simply consist of a suitable resistor instead of capacitor C1. So I see no difference in wiring. The resistor has to be calculated to break the voltage of Pin 8 down to the working range of the op amp.

I made my suggestion because you wrote that I do get some pulses out, but they are not the same as the ones going in.

The cap is there to keep the control DC voltage out of the equation. If you had a fixed divider, the circuit would only work at one of the possible control voltage levels (either no control, 16:9 or 4:3).

Well I simulated it too, so it should work Maybe the actual data levels differ from those in the service manual, or depend on the load you have on the signal pin. Probably need to tweak the cap/resistor values...

I see!

Hagen2000:

The voltage divider would simply consist of a suitable resistor instead of capacitor C1. So I see no difference in wiring. The resistor has to be calculated to break the voltage of Pin 8 down to the working range of the op amp.

I made my suggestion because you wrote that I do get some pulses out, but they are not the same as the ones going in.

 

 

Ah, I'm sorry I misinterpreted you! I thought you wanted to put the divided voltage directly into the microcontroller!

tournedos:

The cap is there to keep the control DC voltage out of the equation. If you had a fixed divider, the circuit would only work at one of the possible control voltage levels (either no control, 16:9 or 4:3).

Well I simulated it too, so it should work Maybe the actual data levels differ from those in the service manual, or depend on the load you have on the signal pin. Probably need to tweak the cap/resistor values...

Yep, I think the reference voltage may be a bit high. I'll experiment some more later when I have more time on my hands. Stay tuned!
 

Got any news? I have an MX6000 now, so I will probably start doing something about this later on

What kind of microcontroller are you using in between? I have a number of old 80C32 boards I built years ago, but I'm not sure I want to start playing with EPROMs anymore. I'll probably get some kind of in-system programmable devkit (yes, I'm lazy), maybe AVR based...

Well, I may still prefer to tap into the nice TTL levels from the audio system instead of the SCART.

Oh well, the server crash ate both your & my posts from last night, so I'll work from memory...

I've been planning to get working on AVRs too for years, so I just ordered an STK500 and some chips. My intention is to build some kind of a "STB-C" that would allow me to control both my Linux VDR and the stupid Nokia STB with Beolink 1000 / Beo4; when it would receive a certain B&O code, the gadget would retransmit a corresponding code/codes to the 3rd party device. Which got me thinking of a third way to implement receiving the remote codes - direct from the remote! However, the 455 kHz IR modules (TSOP7000) aren't available at every corner shop, and the wired solution is probably more reliable.

Once I get something working, I'll try and squeeze it into an ATtiny85

I've also considered using the codes directly from the remote by using a TSOP7000, but I have opted to use the wired solution since it will enable me to control the 3rd party device from the link-system.

So, how is this going guys? Have you got it working?

Not me... I'm mostly at the summer house now, in Beijing for most of August, and can't be bothered with programming until later in autumn In addition, the German webshop where I ordered the TSOP7000s along with some other crap still hasn't delivered after a month, which reminds me to send them a note...

The electronics workshop I've been working on this project at has been closed due to exams and summer vacation since early May. When it reopens in august I will try to finish a working prototype. I have some exciting plans for a masterlink/mythtv-based home entertainment system for my apartment.