DAB and 3.5mm CDC hardware update

[saab95]

I bought the 3.5mm board and parts back in 2014 and I was planning on doing integrating DAB (FM radio replacement in Europe).

Now they are closing the FM broadcasters the next year and I really should finish this project.

Is there any upgrades to the 3.5mm board I should incorporate before starting to solder?

[Seth]

no, I've moved on to bluetooth from 3.5mm; it's just easier to integrate steering wheel/head unit controls.

I'd be interested to see what you come up with when you're done :)

[Karlis]

I don't think anything changed much on the hardware side. I did some work on software before switching over to Bluetooth version of the module. The latest version for 'wired' modules can be found here:

https://github.com/kveilands/SAAB-CDC/tree/wired

Hope this helps.

[saab95]

Yes, I've had a look at the code and looking forward to play with it.

I'm by no means good with electronics and I can't seem to figure out how to place 4 capacitors on the "3.5mm" board...

I've received polarized capacitor for C11-C14 but the board does not indicate polarity. I've looked at the pictures posted on the blog and can barely see that the 3 of the capacitors shows the marking towards the camera. Is this correct???

[Seth]

I'm not sure exactly which version 3.5mm pcb you're working with, but if I'm right, the pcb you have, those caps (c11-14) are not polarized...so are you sure you ordered/received the proper caps? the ones that should go there are little, yellow guys, non-polarized, tantalum caps.

if you can take pics and post them here i can get a better idea of what's going on (pics of the pcb and your mystery caps).

[saab95]

The caps connect pin 1 - 2 and 8 - 7 on both 134PA drivers. I've had a look at the specs for the driver but can't really tell which way the caps should be installed...

Boards
http://imgur.com/a/qNqH9

134PA driver:
http://www.ti.com/lit/gpn/DRV134

Caps:
http://mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeyT350E106K016AT

[Seth]

There's no problem; the caps go in either way; they're not polarized.

[saab95]

Thanks for your reply :-)

It's not that I distrust you but I just want to make sure.

Here's a picture of the cap and it has markings that makes me think it polarised. But I'm new to world of electronics and would appreciate your insight!

http://imgur.com/a/O2eHM

[Seth]

LOL, i actually never noticed the polarization on those caps.

so....the datasheet says to use non-polarized caps. These are polarized. But I've actually used them many times, and never paid any attention to the polarity (because I thought they were non-polarized), so I don't think it matters.

if it makes you feel better, I would put the positive pin of the cap on pin 1 and 8 of the drivers...

sorry for the confusion; this is the first time I've been notified of this :P but as this version is pretty old, I'm not very worried about it.

[saab95]

 then it's solder time!!

[saab95]

I tested my 3.5mm board with a cheap external bluetooth audio dongle and it works perfectly!

Best of all, I can use the free +5v and power the bt dongle from the board :-)
I just hope the 18 mA don't blow the power supply ;-)

[Seth]

I did the same thing before I made a bluetooth pcb; I hooked up a nice Logitech bluetooth stereo adapter thing (it took bluetooth audio input and routed them to 3.5mm or RCA outputs). I also powered it from the 5V regulator. You should be fine; I think the regulator is 500mA or maybe even 1000mA capable :)

enjoy your tunes!

[mcaldwelva]

Hey, I'm working with the 3.5mm module as well. According to the TI specs, we should be using non-polarized caps for C11-C14. But I've been using the caps that Seth specified for a little over a year now and they seem to work fine. I have been trying to hunt down some sporadic high-pitched noise. I don't think it's related to these at all, but I might try swapping them out to be sure.

I've also thought about replacing the 1044 regulator with an 1144 so I can turn off the drivers when they're not in use for a little power savings. Overall seems to be a very nicely designed board though.

The only real question I had was C8. Looking at the as-built, it appears to be reversed wrt to the board?

[Seth]

Hmm, in that picture, C8 does look backwards...

I just know that you need to be aware that there's a -12v rail, so in that case, the positive side of the cap needs to go to ground (since ground is more positive than -12v).

[saab95]

I've mounted the C8 cap like the other caps.

[mcaldwelva]

To close the loop on this, I found a few discussions on the relative unimportance of those sense caps (C11 - C14):

http://www.gearslutz.com/board/geekslutz-forum/719691-drv-134-caps-out-sense.html
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=147

But I couldn't rule them out as a potential source of the noise. I replaced the tantalums
 with ceramics, removed the socket connectors, and rerouted the 3.5mm connector. The combination of these changes apparently did the trick.

[saab95]

I never had any noise issue with my 3.5mm board. It has perfect audio gain compared to current pre-amp boards of bluesaab.

Have you done any mod to the software on your board?

[mcaldwelva]

The first board I built was picking up some high-pitched noise that I was hearing pretty consistently on MP3's -- no problem w/ FLAC. It sounded like some digital noise was being induced before the amplifier, but I couldn't really pin it down. The little hardware update I did seems to have fix it, but unfortunately I don't know for sure where it was coming from.

Yeah, I wrote my own software so that I could integrate it with a sound codec & SD card to make a virtual CD changer: http://github.com/mcaldwelva/iSaab

[saab95]