CM5908/5907 Plug-n-Play Bluetooth upgrade board

[Chrisbike]

Home run brother. Ready to paypal you for the units i requested earlier

[bradnic]

Home run brother. Ready to paypal you for the units i requested earlier

[s1uma1]

Turns out using a separate power supply and ground path totally fixes the digital noise issue like I hoped.

So it's all working now! I just made a short demo video with everything buttoned up inside and functioning. Still work to go but it's getting close.

Omg. This is so freakin' awesome. Please please please please tell me you're gonna sell this... please please please...

[jaysterling]

Turns out using a separate power supply and ground path totally fixes the digital noise issue like I hoped.

So it's all working now! I just made a short demo video with everything buttoned up inside and functioning. Still work to go but it's getting close.

[bradnic]

it probably introduces noise. best to try a battery source to make absolutely sure.

[jaysterling]

you are powering the whole test rig with an actual battery and not a power supply right?

No, I'm using a bench power supply currently. I figured power could only get noisier running on the alternator in the car, so I should get it at least working in the ideal case first. Bad idea?

[bradnic]

you are powering the whole test rig with an actual battery and not a power supply right?

[jaysterling]

Still working on it! Been super busy with work lately working long hours, so time on this has suffered, but certainly not stopped. It's also been a real PITA working with this CSR chip. I've pretty much figured out its quirks at this point but for awhile I was having huge troubles reliably reading/writing the EEPROM that configures the BT chip and (now I realize) mistakenly thought I kept frying the chips.

Anyway, my hope is to get a video up this weekend of it working. Pretty much all the buttons are doing the right things now according to that original faceplate pic I put up. Mic input and phone calls are working. The last thing I have to work through is the analog audio out. I've got it working, but there is digital noise in the output that's higher than I'd like, so next I'm seeing what I can do to eliminate that. The BT chip has differential outputs, then I'm using a TPA6132A headphone amp for the single-ended conversion. When I plug the output of the chip into headphones, the SNR is great, but when plugged into the stereo, the digital noise is present. I'd guess it's like -50 dB down from full scale signal, but it's there. I'm going to try running a separate 3.3V regulator just for the headphone amp with a separate ground path from the rest of the circuit, but any advice is appreciated :)

[Chrisbike]

Update us!

[djjerme]

Did someone confirm that the 5903 has the same mechanism?

[bradnic]

Count me in for 2 boards.

[earthwormjim]

Yeah, after searching around a bit, I see there is already the BT solution out there for the CD43 from Grom like you mentioned. I also read about a wired input solution by DICE for the C33/C43, but everything I read is people complaining about it not working correctly and I think it's NLA. So it seems it's the C33 and C43 that are left out in the cold for tech, that's probably where I'd concentrate. And if those two share the same deck, and also share it with the 5903L like I've read (can't confirm), then that covers a nice range of years and models of BMW cassette stereos with just 2 versions. Anyway, I'm getting ahead of myself...

Grom works with the C43, it hijacks the CD changer functionality.

You don't want to use a C33 though, it has much lower output than the C43 and CD43, and has a very lossy low pass filter.

[jaysterling]

Yeah, after searching around a bit, I see there is already the BT solution out there for the CD43 from Grom like you mentioned. I also read about a wired input solution by DICE for the C33/C43, but everything I read is people complaining about it not working correctly and I think it's NLA. So it seems it's the C33 and C43 that are left out in the cold for tech, that's probably where I'd concentrate. And if those two share the same deck, and also share it with the 5903L like I've read (can't confirm), then that covers a nice range of years and models of BMW cassette stereos with just 2 versions. Anyway, I'm getting ahead of myself...

[bmwman91]

The CD43 and similar are probably entirely different beasts. I believe that the audio stream in those is digitally transmitted from the CD transport to the main DSP chip on the motherboard (via either PCM or I2S format). Beyond that, the DSP chip is likely to engage in some handshaking and error detection with the CD transport and the control IC on it. Of course, it does not mean that it is impossible...only that it is more challenging. I have a beaten / hacked up CD43 laying around at home that I'd be up for volunteering for experiments at some point.

A much more likely avenue to go with on the CD43 and the like is to spoof the I-BUS bus and make the head unit think that it is connected to a CD changer. Grom's Aux/BT input units do this. If you went the route of installing a daughterboard to intercept faceplate functions and the display, you could do all sorts of stuff with the CD changer input. I decoded the entire faceplate protocol of the CD43 like 5 years ago and it is just a 5 wire master/slave SPI setup (5th wire serves as a heartbeat/arbitration signal IIRC). The display is super easy to control, and most of the buttons talk to the motherboard via SPI. I think that the power and eject lines are the only ones that have dedicated signal lines. Anyway, I bought all of the full internal electrical schematics for it back when I was messing with this.

Sorry to hijack...

[jaysterling]

...how is the heat build up. You're adding a lot more components in the unit, and I am just wondering about the excess heat radiated by the active and passive components when it's installed in the dash with everything else around it.

Keep in mind I removed a much larger number of components crammed in there before adding my little board. The whole thing pulls less than 100mA and has plenty of room to breath.

I'm still on board for this when you have it up for either beta or whichever.. Also, have you thought of doing a Kickstarter to get some funds for production rolling in? Get people committed to the initial rollout/beta testing? I'd be down for that.

I might do a kickstarter, that's not a bad idea. I want to have a fully working prototype before taking people's money though. I don't want to be holding on to people's money for a long time.

I am very interested and I want to find out what will be needed for it to be compatible with a CD43 since it does not have a tape, and whether there is a possibility for it to show titles and artist names like Grom iPod adapter or Dice.

This version wouldn't be compatible with anything but the CM5908, 5907, and 5905, since they turn out to use the same cassette deck and pinouts inside. (I actually have not tested anything in a 5907/5905 yet, but the deck is the same, the cables are the same, it's probably the same).

That said, IF this goes well, I've got my eye on the C33 and C43/CD43. But it would be a whole different board and require reverse-engineering the pinouts of the tape/CD deck inside.