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Subaru Radio Digital Control Data Decoded


jazzymt

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Wow! Solid work , are you diving into the heater controls next?

There's still a fair bit of work to do, but yes. There are 3 serial interfaces I need to manage to have all this work flawlessly & my current microprocessor is limited to 1 and doesn't have the speed to emulate the SPI bus the CD changer uses. I have a beefier chip I need to start playing with that can run the final electronics.

 

Also - I need to finish the CD changer interface so that it can fully emulate comms and interrupt 2-way communication between the radio & CD changer at-will. I'm pretty close, but as with anything - the last 10% usually takes 90% of the time.

 

Once that's set, I just need to design and build a new board - do some testing, etc. It's going to take some time, but things are going well now. I don't think there are any "huge" unknowns left now that I have the bluetooth module up and running.

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Well - the good news is - the bluetooth module is working great. It's easy to set up, connect & control. I used A2DP to stream music from Pandora and built-in music player no problem. The sound quality also seems very good.

 

The bad news is - it's really designed to be used with headphones so the built-in analog output is too quiet when connected to the CD player. I need to figure out if I can either bump up the voltage level or I may have to set up an external dedicated DAC with line level outputs if that causes too much distortion.

[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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How is the sound quality compared to a dedicated line-in, or a CD playing in the CD changer? One of the issues I had with my Leptronix line-in, and that I now have with the A2DP on my iSimple Gateway, is that sound quality is at least a little off from the CD or built-in line-in quality. It sounds almost like the high (and maybe low?) frequencies are clipped, and when the A2DP volume is up all the way, there is some static.
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The sound quality is definitely compromised by the signal level & impedance mismatch. It's usable, but it's not good enough for me. I'm going to try using passive transformers and JFET's (2 separate options - not together) to see if I can boost the signal & match the impedance better, but they may both add distortion and clip frequency response. If I have to - I'll use a dedicated DAC on the digital audio output to ensure audio quality.
[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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Well - I've done a little research on dedicated DAC's - I think this is what I'm going to do. I could screw around with trying to bump up the current analog signal and get halfway there - or - I could connect a dedicated DAC with 2V RMS 10kΩ impedance line level output to the digital audio output and just be done with it.

 

Hrm...I wonder which one will satisfy the audiophile in me? :rolleyes:

[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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That sounds good! Do you think the volume level will be roughly the same as from the normal sources on the headunit?

That's the plan. Tomorrow after I go AutoX'ing I plan to hit the analog output with my crappy oscilloscope for comparison. The 2V RMS output of a dedicated DAC should be far superior - at the very least in volume, but likely higher quality too.

 

I'll hook up the logic analyzer on the digital output tomorrow too to make sure the DAC I picked out has the right PCM compatibility.

[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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Some more news. I had to contact the MFG of the bluetooth module, but got an updated firmware that supports the I2S digital audio output I need. Module is flashed - all is good.

 

Unfortunately the TSSOP package for the DAC is just too damn small to solder leads on by hand. I've soldered & de/re-soldered so many times I think the 2 chips I got are probably both junked. So - I ordered some prototyping supplies and I'll make a breakout board for it so I can finish devel/testing.

 

Tomorrow I'll switch back to development on the radio/cd interface while I wait for more supplies & parts to show up. :)

[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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IDK how you do this stuff... I guess that's why I'm an aerospace/reliability engineer and not an electrical/computer engineer :lol:

 

 

 

This should beat my unweildy FiiO E6 amp (great $26 item!) + phone/mp3 player + aux-in with ground loop isolator combo. I'm anxious to see the final product and review of the resulting audio quality :)

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Got my DAC all soldered up on a breakout board. Note the fail on the first attempt to solder individual wires. :rolleyes: This thing is just too damn small (as you can tell by the penny reference). Oh well - it was worth a try.

 

The breakout board looks great though & should work (crossed fingers). I might be able to try it out after I get some lunch, but it is Valentines day weekend - gotta keep the wife happy. If I don't get to it today, I'll definitely test it out tomorrow.

 

...updates to come...

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[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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Nieeeezzzz. Well - I had to make one little correction to the board, but the DAC performs fantastic. Audio quality is excellent - night and day vs. the crappy built-in analog output. Volume is also perfect - clearly audible at 4-6ish and plenty loud by 15ish.

 

Next is Radio startup w/o any CD changer - then full emulation & live switching between CD changer & Bluetooth via microprocessor control (woot!).

 

Obligatory Youtube video:

 

[ame=http://www.youtube.com/watch?v=7o2hgB-RnsA]Streaming Bluetooth A2DP Audio w/DAC - YouTube[/ame]

[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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Will the phone interface and will you have a remote mike that goes along with the unit?

 

Short answer - I don't know, but I would like to add handsfree.

 

Now that an external DAC is thrown into the mix - switching between streaming and handsfree could be tricky. I will need to play with the module some more - technically it supports it, but I might have to add an ADC for a mic and run full-time digital for handsfree to work since I'm not using the built-in analog...just not sure how it will work.

 

:) I am assuming that if one had a carputer with a bluetooth output this would work fine? If so, count me in. Thanks for all your work on this project.

 

Yea - it will be compatible with any bluetooth device - except possibly iPhones since Apple crippled their bluetooth interface. I'll have to do some more digging, but at one time at least you needed an authentication chip to allow an iPhone to stream over A2DP (which this module does not have).

[CENTER][URL="http://legacygt.com/forums/showthread.php?t=18504"]Subaru Plug & Play Aux-in Mod[/URL][/CENTER] [CENTER][URL="http://www.jazzyengineering.com"]www.jazzyengineering.com[/URL][/CENTER]
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