The Workbench

Re: SCART Datalink/AVL- seeking advice

magnushj — Sat, 19 Jul 2008 07:44:21 GMT

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.

Re: SCART Datalink/AVL- seeking advice

tournedos — Sat, 05 Jul 2008 06:13:57 GMT

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...

Re: SCART Datalink/AVL- seeking advice

mhw — Sat, 05 Jul 2008 05:53:06 GMT

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

Re: SCART Datalink/AVL- seeking advice

magnushj — Sat, 17 May 2008 15:38:16 GMT

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.

Re: SCART Datalink/AVL- seeking advice

tournedos — Sat, 17 May 2008 14:19:06 GMT

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

Re: SCART Datalink/AVL- seeking advice

tournedos — Thu, 15 May 2008 07:29:05 GMT

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.

Re: SCART Datalink/AVL- seeking advice

magnushj — Tue, 22 Apr 2008 17:15:03 GMT

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!

Re: SCART Datalink/AVL- seeking advice

magnushj — Tue, 22 Apr 2008 17:11:09 GMT

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!

Re: SCART Datalink/AVL- seeking advice

Hagen2000 — Tue, 22 Apr 2008 07:30:35 GMT

I see!

Re: SCART Datalink/AVL- seeking advice

tournedos — Tue, 22 Apr 2008 06:03:46 GMT

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...

Re: SCART Datalink/AVL- seeking advice

Hagen2000 — Tue, 22 Apr 2008 03:42:31 GMT

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.

Re: SCART Datalink/AVL- seeking advice

magnushj — Tue, 22 Apr 2008 02:10:47 GMT

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!

Re: SCART Datalink/AVL- seeking advice

Hagen2000 — Mon, 21 Apr 2008 16:07:39 GMT

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.

Re: SCART Datalink/AVL- seeking advice

magnushj — Mon, 21 Apr 2008 03:17:05 GMT

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.

Re: SCART Datalink/AVL- seeking advice

magnushj — Thu, 10 Apr 2008 13:05:44 GMT

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.)