Author Topic: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )  (Read 4744 times)

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Offline XOIIO

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Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« on: November 12, 2015, 08:24:08 pm »
Hey all, I have this bluetooth receiver module for a project I'm working on (and am almost done) however I've had a couple issues.

http://www.ebay.ca/itm/Bluetooth-BLK-MD-SPK-B-Stereo-Module-Audio-Transceiver-EEPROM-V2-0-EDR-/370916284758?ssPageName=ADME:X:AAQ:CA:1123

First one was the microphone not working, however I think it's just not enabled for this version, disappointing, but not a major issue.

The main issue is noise on the speakers, it sounds like general radio interference, a bit of buzzing, some beeping, kind of static-y (can't find any cables I could use to record it right now)

Anyways, this noise changes when I touch the antenna, with my finger or an alligator clip wire this reduces the noise level drastically, though it's still audible with no audio playing.


I'm wondering if you guys know of any way I could reduce this. My first thought was an external bluetooth antenna, but I don't have time to wait for it to get here, what seems odd is that adding in just a random bit of wire helps, when bluetooth needs a pretty specific shape of antenna pattern.

I also am going to try coupling capacitors on the speakers, and perhaps on the power supply (the noise was actually louder when connected to a Lithium ion battery than when it was connected to my power supply) though considering touching the antenna is changing this, I'm not sure if these would work or not. I've tried some 22uf electrolytic on the speakers (only the negative side, but the diagram on the wiki shows some on both) to no avail, and unfortunately everything will be closed for quite a while yet so I'll have to see what I can salvage.

I think I saw mention of 200 or 300uf capacitors being an appropriate value for this sort of use? Seems a tad high, but I haven't done any audio stuff before this.

www.elecfreaks.com/wiki/index.php?title=BLK-MD-SPK-B

edit: also got it to be fairly quiet just now but there's a slight rhythmic clicking, about twice per second.
« Last Edit: November 12, 2015, 08:27:03 pm by XOIIO »
 

Offline XOIIO

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #1 on: November 12, 2015, 10:23:33 pm »
From what I've been reading, seems like it's a ground loop issue, and a 1:1 isolation transformer is in order, except that I don't think I can source something like that locally :/

Edit: wait, not a ground loop, the thread I was reading had the guy using two separate boards (receiver and separate amplifier), maybe an isolation transformer would work though. I'm going to dig through my boxes of stuff and find some ferrite rings and see if those have any effect on reducing noise
« Last Edit: November 12, 2015, 10:38:49 pm by XOIIO »
 

Offline XOIIO

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #2 on: November 12, 2015, 10:48:17 pm »
This is the exact same noise I'm getting

Offline XOIIO

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #3 on: November 13, 2015, 01:30:02 am »
Seems there is a way I get can 1:1 transformers that look the same as ebay cheapies (for $12 each, yeesh http://www.be-electronics.com/product_p/nte-1.htm) However I don't know if these transformers would even work to correct this, these audio lines are coming right from the board, no other amplifiers, no AC voltage that could leak and cause issues, the noise is pretty much part of the audio signal the board is outputting it seems.

I might have an old laptop sitting around I can get a mini coax cable from, but that noise is still audible when no music is playing, or in very quiet parts. I could maybe cut the antenna trace on the board and rely on the external antenna completely though I don't know if that would work.

I've also tried a bit of copper tape over the board (Except the antenna) to shield it and that did not work. Maybe completely surrounding the board in copper tape and having a mini coax antenna coming out would work? (would be tricky though due to how the board is set up).

Offline XOIIO

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #4 on: November 13, 2015, 04:12:04 am »
I found a board for some sort of audio input/output with some 1:1 transformers, and two 386D jrc mono amplifiers, however the transformer just makes everything quieter, and I can still hear the interference, uuuuhg

Does anyone have any ideas on this at all? I'm at my wits end with this, it's ridiculously frustrating when I can't find any solutions or really even that many other posts/articles or anything with this issue.
« Last Edit: November 13, 2015, 04:16:02 am by XOIIO »
 

Offline mich41

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #5 on: November 13, 2015, 04:46:23 am »
The schematic you linked calls for capacitors on 1V8 and VBAT.
 

Offline XOIIO

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #6 on: November 13, 2015, 06:04:05 am »
I had a 22uf one hooked up to the main supply, I went out and bought a couple 47uf ones, this made no difference, I brought a lead out for the 1v8 one as well without any luck. I'll have to find an AC one somewhere with hopefully a somewhat close value for the rst pin but I don't see how that one would make any difference (also don't see why they have a signal going to the rst pin at all times) - edit: that's not an ac cap with 475 written under it, it's a switch. Not sure what that 475 is doing there, seemed a little high)

edit: also found this which mentions 1v8 is for the buttons, so that won't really be needed, and he seems to have just wired it up right to the power source and there's no mention of noise issues. http://www.instructables.com/id/DIY-Bluetooth-Headphones-v20-Improved/?ALLSTEPS
« Last Edit: November 13, 2015, 06:09:56 am by XOIIO »
 

Offline XOIIO

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #7 on: November 13, 2015, 08:17:17 am »
I can't find anything else, the only thing left I can think of is that it's a defective board. That means that I will have to either see if some sort of antenna setup will make some sort of improvement and not have it randomly get louder, or go without for two damn months, I'd never get another module here in time, it took a month for this one.

Problem is that it was completely random when the noise got louder with an extra antenna wire, so that might pop up at any time and render them useless. Uhg.

Offline Retch

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Re: Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )
« Reply #8 on: September 30, 2016, 02:43:54 am »
A little bit late, but I think my answer will help other people to solve this problem. You only have to do is to cover the antenne with aluminium foil (like I did on the attached pictures). Have fun!
 


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