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Old 04-15-2017, 11:45 PM   #76
earthwormjim
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That module should have provisions for an antenna pin. Looks like if you desolder the 0402 jumper leading to the antenna, and move it over to the left position, that lets you wire an antenna to pin 43.

I'm guessing what you did, is you messed up the impedance matching of the antenna, so you ended up weakening the RF signals. It's no longer a nice fraction of a wavelength.

Normally those little modules (FCC certified ones) have a shield covering everything except the antenna, wonder if that might help?

Last edited by earthwormjim; 04-15-2017 at 11:51 PM.
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Old 04-16-2017, 09:33 AM   #77
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Originally Posted by earthwormjim View Post
That module should have provisions for an antenna pin. Looks like if you desolder the 0402 jumper leading to the antenna, and move it over to the left position, that lets you wire an antenna to pin 43.

I'm guessing what you did, is you messed up the impedance matching of the antenna, so you ended up weakening the RF signals. It's no longer a nice fraction of a wavelength.

Normally those little modules (FCC certified ones) have a shield covering everything except the antenna, wonder if that might help?
Oh ok, makes sense about killing the impedance matching, so it's just the reduced signal strength that's making the noise go away.

The problem with the external antenna solution is the pick-n-place machines that will be doing the assembly can't desolder components right? So I'd need to try to source some modules that already had the right jumpers soldered on, which I'm not sure is possible. I can't imagine manual rework of each module is cheap. If f I did go that route, I'm also clueless what I'd actually do with the antenna design to fix the problem.

So you don't think moving the chip as far that corner as possible, adding a top ground plane + extend the bottom ground plane up around the chip would do anything? I gotta think this can be solved without an external antenna since any run of the mill BT receiver uses a similar module + chip antenna and they don't have this problem, even without a shield over the module. When you look at one though (I tore apart a cheapo one I had) it'd definitely a 2 layer ground plane with lots of stitching that fills everywhere except right under the antenna, all things I'm not currently doing.
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Old 04-16-2017, 07:21 PM   #78
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Jay, I'd test out first if I'm right about having to move the jumper, I'm just basing it off your pictures. See if there is continuity between that pin and the antenna already. Where did you get that module anyway? If ordering from Alibaba, you should be able to specify from the vendor, or they may have an external antenna version.

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Originally Posted by jaysterling
I gotta think this can be solved without an external antenna since any run of the mill BT receiver uses a similar module + chip antenna and they don't have this problem, even without a shield over the module.
Most that are FCC certified, do have a shield over the module.




Sounds like it is time to bust out the copper tape, and see where you might need ground planes or shields.
On my bluetooth project, my mating board had all available space filled in with ground pours.

You could also extend your PCB underneath the module's antenna, and pour in a ground plane. Covering underneath part of the PCB antenna with ground, should weaken RF signals like your added wire does too. You can test with strips of grounded copper tape.


Quote:
Originally Posted by jaysterling
So you don't think moving the chip as far that corner as possible, adding a top ground plane + extend the bottom ground plane up around the chip would do anything
It could very well help, if you can move the module and wire it up with thin leads, test it out. On the power supplies I designed, I ended up putting stuff on flexible magnetic wire, and moving it around while powered up, to see if my EMI emissions changed in real time.

Last edited by earthwormjim; 04-16-2017 at 07:30 PM.
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Old 04-17-2017, 09:01 AM   #79
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Jay how close are you to being able to add pre-outs? A lot of premium sound cars have bad amps, and I bet many folks have bypassed the premium amp by now. I have my car harness setup to support both pre-out and the inline premium amp so I'm ok without pre-out support for now. But I would definitely prefer a pre-out arrangement as I'm sure most folks would.

Not something needed for a minimal viable product version of your board, but should be high on the dev list.
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Old 04-17-2017, 09:41 PM   #80
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Originally Posted by earthwormjim View Post
Sounds like it is time to bust out the copper tape, and see where you might need ground planes or shields.
On my bluetooth project, my mating board had all available space filled in with ground pours.
Gave that a shot today. I didn't have copper tape (ordered some) so I took a shield off some junk I had and soldered on a lead so I could ground it and hold it in various positions. Covering the non-antenna part of the BT module didn't change anything unfortunately, nor did covering just my analog section (as expected, since the noise is there without the audio cable even being plugged in). The positioning below kills it though:



The most crucial area to make the noise go away seems to be the most forward section of that shield, where there is currently no PCB or ground planes, which seems kinda relieving since there are known improvements I can make there. This also kinda makes sense because the unbalanced audio out cable is right behind the shield, and some other audio mixing/EQ circuitry is on the vertical board that it reaches over.

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You could also extend your PCB underneath the module's antenna, and pour in a ground plane. Covering underneath part of the PCB antenna with ground, should weaken RF signals like your added wire does too. You can test with strips of grounded copper tape.
All the datasheets I read say to keep copper out of that area right underneath the antenna. They're still effective like that? Then again, it still streamed music with a wire soldered on the antenna... I suppose it's just a trade-off of range vs. EMI in some cases like this?

Still thinking I should extend the PCB frontwards as far as possible and use stitched ground pours on both sides, then shift the BT chip as far away as possible. Hopefully it doesn't require some kind of vertical shield soldered on the board... I've got the copper tape coming tomorrow so I can at least try building up an extended ground plane with that.
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Old 04-17-2017, 10:50 PM   #81
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Cool, so looks like you found what was picking up the RF emissions; the EQ circuitry and/or the audio cables.

Hopefully you can solve it by relocating the module as you were saying. If relocating or more filled out ground planes doesn't help, you could use a transistor PCB heatsink to act as a verticle shield, similar to what you have now.
They're pretty cheap.

Something like this:


https://www.alibaba.com/product-deta...499402903.html

Quote:
All the datasheets I read say to keep copper out of that area right underneath the antenna. They're still effective like that? Then again, it still streamed music with a wire soldered on the antenna... I suppose it's just a trade-off of range vs. EMI in some cases like this?
Any point of the antenna that has a ground underneath it, is no longer an antenna, so you effectively reduce the antenna length to some odd value that deviates from 1/4 or 1/8 of a wavelength, similar to what your wire does. But definitely scratch that suggestion, shielding is way way better to do, and you found what to shield.
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Old 04-18-2017, 03:30 AM   #82
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LDOs are linear regulators
Yep. I was asking why a LDO would be more quite then a non-low-drop-out linear regulator - both should be running an op-amp internally. And both sinking excess current as heat. Even so, unless you have some unstable feedback internally, both should be about the same.
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Old 04-18-2017, 07:55 AM   #83
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Yep. I was asking why a LDO would be more quite then a non-low-drop-out linear regulator - both should be running an op-amp internally. And both sinking excess current as heat. Even so, unless you have some unstable feedback internally, both should be about the same.
They're not, and I never implied otherwise. They're cleaner than a buck regulator would be. Was pointing out his 3.3V supply is clean, and not to look there for noise issues.

Last edited by earthwormjim; 04-18-2017 at 12:30 PM.
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Old 04-19-2017, 03:18 AM   #84
george graves
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Everyone knows that!

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That's good you are using separate regulators, and LDOs are super clean.
Now can you see my confusion? You specifically mentioned LDO and not just jelly bean linear regulators. That's all. So that's why I was asking. No harm, no faul. Carry on!
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Old 04-19-2017, 11:37 AM   #85
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I really love seeing projects like this, its sad that I longer have enough time on the side for fun things like this. good for you! also check you PM I'll be sending you a message.
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Old 04-22-2017, 12:50 PM   #86
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Dealing with premium amp bypass

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A lot of premium sound cars have bad amps, and I bet many folks have bypassed the premium amp by now.
Pretty sure this is what Barry was getting at earlier in the thread:
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Brilliant. Is this to be used with the premium sound amp or does it have an onboard amp?
As I explained, the current board doesn't add pre-outs, so it doesn't matter whether/not you have the premium amp. It does matter if you've bypassed the premium amp though, since the OEM radio/head unit only supports speaker level outputs.

If you don't have an aftermarket amp you need to connect your OEM radio speaker outs to your speakers and you're limited to 5W per channel. If you do have an aftermarket amp, you need to use its speaker level inputs or not use it all with this version of Jay's board.
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