Renault Scenic II - SPDIF PC

**Vicne** · 06-26-2005, 05:57 PM

Afters years of thought, I finally achieved my carPC v1.0.

Quick highlights :
- SPDIF connection to the head unit, hacking the CD changer connection
- Completely removable solution. Not a single modification to the car.
- Tank battery circuit to allow for clean shutdown.

I'll probably set-up a website to give more details, but you'll find a few pictures attached. The PC was build in a metal U shape that can be unfolded for easier maintenance. It is tailor-made to get in the center console of the Renault Scenic, under the armrests.

When I discovered that the integrated headunit had no AUX input and that the CD changer had no analog connection to it, I was seriously disappointed. I tried an FM modulator but the quality was really poor... I then found that this CD changer actually sends an SPDIF signal to the headunit, and checked with my home PC that standard PC levels were correctly recognized. I thus placed a little relay to switch the headunit SPDIF input from the CD changer to the Epia SPDIF output when the PC is on. The control wires are always connected to the CD changer, so the head unit is fooled into thinking the SPDIF comes from the CDs. Who said sound quality of EPIA motherboards is not perfect ??? :-)

One specific requirement was that I was allowed no modification to the car as it belongs to my company. No screws, no holes, no glue, nothing. The console place seemed to be the best bet as it already contains a cigare-lighter socket. I had to run 2 wires from there to the headunit (one for SPDIF, one for activating the relay) and temporarily replace the cigar-lighter socket with a more reliable one. Not easy but well, I succeeded thanks to the help of a few guys at http://forum.planeterenault.com . One advantage is that the installation is completely hidden as the console still can be fully closed once the screen is disconnected.

Finally, as the cigar lighter socket is only powered when the accessory line is on, I had to find a solution to power the PC during its shut down (or hibernation) and settled on a 10 Farad capacitor...
Just kidding. I'm using an SLA tank battery of course :-)
The circuit - attached - uses 2 diodes (MBR3045 is a dual diode) and a current-limiting resistor, and was designed following the advices and opinions posted here, there and finally there :-). The 3.4 Ah SLA is probably overkill, but if the shutdown takes longer for a reason or another... better safe than sorry.

Thanks to all mp3car forum users that helped me in one way or another :-).

Note : The screen is currently not fixed and sits in the glove box.

**mox** · 06-27-2005, 07:53 PM

Argh, you beat me there by one day! I've just finished doing the same SPDIF hack to my HU tonight

. I guess your Scenic has a VDO "Tuner List" HU too, right?

A few questions about your setup:

- You are keeping the changer connected to enable the HU's SPDIF input. Does this mean you always have one or more CDs inserted? AFAIK, an empty changer is automatically ignored and skipped by the HU when switching audio sources. This is why I bought an aux interface from connects2.com (type VRNX001). It acts as a fake cdchanger and also contains an analog-to-SPDIF encoder.

- Furthermore, how can I get the audio line-in (and the mic input) of the epia to be mixed into the SPDIF output? I haven't tried much yet (nor did I search..) -- all i noticed is that I couldn't hear anything from both inputs. Neither of them is muted in the mixer panel and they are being output properly to the ANALOG line out.

Anyway, congrats on a hack well done. I am pondering a smart PIC-processor based interface so I can use the HU's stalk control to send commands to the PC. The stalk control in my Clio is actually a simple 3x3 matrix of switches. I am quite sure the Scenic is identical.

EDIT: I did a search on the analog input issue. There doesn't seem to be a solution yet. A software pass-thru might do the trick, but it will increase cpu load. Anyone?

**LagunaICE** · 06-28-2005, 07:08 AM

Originally Posted by mox

Argh, you beat me there by one day! I've just finished doing the same SPDIF hack to my HU tonight

. I guess your Scenic has a VDO "Tuner List" HU too, right?

A few questions about your setup:

- You are keeping the changer connected to enable the HU's SPDIF input. Does this mean you always have one or more CDs inserted? AFAIK, an empty changer is automatically ignored and skipped by the HU when switching audio sources. This is why I bought an aux interface from connects2.com (type VRNX001). It acts as a fake cdchanger and also contains an analog-to-SPDIF encoder.

I am very interested in hearing more on this. Can the trick be done on HU without an actual CD changer beeing connected or not?
Vicne, could you post more detailed pics and changer hack pinout diagram for us?
BTW I have a "Tuner List" ...

**Neil_Strudwick** · 06-28-2005, 08:50 AM

Thats fnatastic, Gives me great ideas of how to do it in the megane! Have you seen this post with someone else having a screen in the dash. Might be an idea?

'03 Renault Megane II - Lilliput 7" Installation

**mox** · 06-28-2005, 09:27 AM

Originally Posted by LagunaICE

I am very interested in hearing more on this. Can the trick be done on HU without an actual CD changer beeing connected or not?

The cd changer uses SPDIF for audio and D2B (a different set of pins on the blue mini-ISO connector) as control port. The HU will only enable its SPDIF input after getting specific data via D2B. This is one of the purposes of the Connects2 adapter (VRNX001). It mimics a cd changer (1 cd, containing 1 track

) so the HU will enable its SPDIF input. Secondly, the adapter contains a separate analog-to-SPDIF converter (stereo RCA analog in).

The French URLs below (which handle the issue of linking a VDO Dayton CHM604 MP3 cd changer to a Tuner List HU) show you the pinout of the blue 8-pin mini-ISO. Ignore the round DIN-plug at the side of the changer. I will post the pinout of the stock cd changer (10-pin ISO) when I get home.

http://www.forum-auto.com/sqlforum/s...ujet217329.htm
http://perso.wanadoo.fr/sebire.phili...hargeur_cd.htm

**mox** · 06-28-2005, 02:13 PM

Originally Posted by mox

I will post the pinout of the stock cd changer (10-pin ISO) when I get home.

Here are pictures of the stock cd changer in my Clio and its connector (pin numbers in green). The pinout of this 10-pin ISO connector appears to be as follows:

1, 2, 4 and 10 = GND
3 = SPDIF output (to HU)
5 = CD UART +
6 = not connected
7 = 12V switched (from HU)
8 = 12V permanent
9 = CD UART -

D2B traffic is handled by the UART pins.

**Vicne** · 07-10-2005, 08:29 AM

Sorry all for the late replies, I was on holiday

Originally Posted by mox

Argh, you beat me there by one day! I've just finished doing the same SPDIF hack to my HU tonight

. I guess your Scenic has a VDO "Tuner List" HU too, right?

Yes, the damn "no-aux" Tuner List

- You are keeping the changer connected to enable the HU's SPDIF input. Does this mean you always have one or more CDs inserted? AFAIK, an empty changer is automatically ignored and skipped by the HU when switching audio sources. This is why I bought an aux interface from connects2.com (type VRNX001). It acts as a fake cdchanger and also contains an analog-to-SPDIF encoder.

Yes, I've seen it, but I really think it's not worth the 100 EUR or so, that are mostly due to the Analog>SPDIF converter I don't need. So you're right, I always have a few CDRs in the changer : It's definitely cheaper

and the only drawback is that every 80 minutes, the SPDIF is muted during a few seconds while the changer loads a new CD. This would probably disappear if I'd only put 1 CD in the changer but I don't really care for now.
A big advantage of my setup is that I have a simple DPDT relay that switches the SPDIF input from the changer to the PC once the PC is started, so if I don't start the PC or if I remove it from the car for maintenance, the setup is transparent and the changer is fully functional

. Of course, it only works if you have a cd-changer...

- Furthermore, how can I get the audio line-in (and the mic input) of the epia to be mixed into the SPDIF output? I haven't tried much yet (nor did I search..) -- all i noticed is that I couldn't hear anything from both inputs. Neither of them is muted in the mixer panel and they are being output properly to the ANALOG line out.

Well, I have no use for that right now, but indeed, I think "line-in to line-out" is a kind of "shortcut" that doesn't go through the SPDIF encoder. As you say, it would suffice to go through a higher level application that would just sample these inputs and pass them through to the "wave out" to have them go "the long way" and via the spdif encoder. In that case, the "Playing" mixer settings would of course have no effect, but the "Recording" ones would. Probably using any realtime processing effect with all settings at zero would do the trick, using "some" CPU (depending on how well the effect is written)...
It shouldn't be too hard to write one, but I don't have time or need for that right now.
Maybe another way would be through a virtual sound driver such as the one included in TotalRecorder...

Anyway, congrats on a hack well done. I am pondering a smart PIC-processor based interface so I can use the HU's stalk control to send commands to the PC. The stalk control in my Clio is actually a simple 3x3 matrix of switches. I am quite sure the Scenic is identical.

Mmmh, don't know, but if I were you - and that's in my low-priority plans - I'd purely and simply try to emulate the control protocol of the CD changer...
Regarding that, the status of my research is that among the protocols listed on http://www.mictronics.de/?page=cdc_proto , the only one that uses asynchronous two wires transfer (RX + TX + no clock) is the Blaupunkt one. Moreover it uses the same wires as our Tuner List, so that's encouraging : compare the last page of http://www.blaupunktusa.com/NR/rdonl...5E/0/MDP01.pdf to the attached pinout of the Tuner List (taken from this post). I also had confirmation by bistie on planeterenault.com forums that once the levels are adapted (5V TTL to 12V RS232) the protocol is compatible with a PC serial port. Still have to investigate exactly the protocol grammar, but that would allow not only next/previous/pause but also cd change *plus* feedback of CD#/track# to the dashboard. If you're ready to use a PIC, I think this path is simpler and worth the try, isn't it ?

Vicne.

**Vicne** · 07-10-2005, 09:26 AM

Originally Posted by Neil_Strudwick

Thats fnatastic, Gives me great ideas of how to do it in the megane! Have you seen this post with someone else having a screen in the dash. Might be an idea?

'03 Renault Megane II - Lilliput 7" Installation

True, that's nice, but that wouldn't fit on the Scenic because it only has one ISO frame (no spare space under the HU)... Moreover, in my case, as this car belongs to my company, I can not modify it permanently.

My best bet for now would to fix the screen to a big clip that would "bite" the top of the Scenic's dashboard to have the screen almost at the same place as the factory GPS option - see http://www.autotrack.nl/img/news/jul03/Scenic.gif

**Vicne** · 07-10-2005, 10:05 AM

Originally Posted by mox

The cd changer uses SPDIF for audio and D2B (a different set of pins on the blue mini-ISO connector) as control port. The HU will only enable its SPDIF input after getting specific data via D2B.

Thanks for the details, mox. By the way, do you have more information on that D2B format and that "specific data" needed ?

This is one of the purposes of the Connects2 adapter (VRNX001). It mimics a cd changer (1 cd, containing 1 track

) so the HU will enable its SPDIF input.

I didn't know about the CD1/TR1. And what "running time" information does it send back to the player ? I mean, when does the head unit know that it has to change track or disk ?
If the changer operates stand-alone in that regard, and the head unit only displays the cd#/track#/time info without interpreting them, that would be cool because we could send other informations to the display (time 12:34 could mean 12st album by artist number 34..., etc).
Might be worth thinking of it...

**mox** · 07-10-2005, 02:27 PM

Originally Posted by Vicne

Thanks for the details, mox. By the way, do you have more information on that D2B format and that "specific data" needed ?

Um, no

Actually I am sort of hoping for you to come up with a cool $5 PIC-based interface in the near future

My experience with PICs is still next to zero, but I intend to learn more about them, e.g. by building a little development kit and starting off with a simple project.

I didn't know about the CD1/TR1. And what "running time" information does it send back to the player ?

The OEM display in my Clio's dash is somewhat limited, as it only displays track# and cd#, so no remaining time or anything. I guess the ppl of connects2.com have found a way to mimic a single cd with a single endless track. Once I select the cd changer as a source, the HU permanently displays "CD1 - TRACK 1".

If the changer operates stand-alone in that regard, and the head unit only displays the cd#/track#/time info without interpreting them, that would be cool because we could send other informations to the display (time 12:34 could mean 12st album by artist number 34..., etc).
Might be worth thinking of it...

Somehow I am glad my display is limited