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Noise/interference on bluetooth audio module? (BLK-MD-SPK-B )

Discussion in 'Radio and Wireless' started by XOIIO, Nov 12, 2015.

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  1. XOIIO


    Mar 11, 2014
    Hey all, I posted this on eevblog but with a bunch of views and only 1 response from someone else, and a crapload of searching to no avail, I figured I would try here.

    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.

    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.

    edit: also got it to be fairly quiet just now but there's a slight rhythmic clicking, about twice per second.

    I've tried 22uf capacitors on the speakers, a 1:1 isolation transformer on the speakers (with and without caps), 22 and 47uf capacitors on the power input, and a 47uf capacitor connected to 1v8, all without any change.

    I've noticed that touching, or connecting a wire to the antenna makes the sound much quieter, though you can still hear it and occasionally it still gets very loud.

    This is exactly the sort of stuff I'm hearing, except that I don't have any other circuitry attached, the only posts I can find about noise ended up being a ground loop problem relating to an external amplifier. As you can see, I have the board by itself, mounted to a perfboard so that I could break out the connections more easily.


    Attached Files:

  2. davenn

    davenn Moderator

    Sep 5, 2009
    hi there

    dunno what that big black box at the end of your post is ??? try reposting it

    looking at your circuit pic ... its dreadfully messy and may be some or all of the noise reason
    its also possible you have zapped the circuit with static and damaged it, very easily done when using incorrect working conditions

  3. XOIIO


    Mar 11, 2014
    That box is supposed to be a youtube video, must not be displaying properly for you, its just an example of the noise.

    The problem is the noise sounds like data interference, and while it does look a bit messy, there's as much clearance as I could get between the wires, the gap between the pads on this thing are the smallest that I've ever dealt with. I thought it might be from that too but with the way the noise sounds, if it was from that, surely it would be a hum or buzz, this is very distinct, going from what sounds like radio interference and clicking, to a click twice a second after some time of not receiving any audio from the phone I have it paired to. If I trigger any audio it goes back to the first sounds.

    I'm starting to think it might be a defect in the board itself, and considering that the microphone doesn't work, I will probably try and get another one, I was going to anyways since I wanted to have the mic working and this one would be temporary.

    The problem is that I only have a week and a bit before I will be out of the country for two months, and I really wanted to have these finished up, it took a damn month for this one to get here, if I can't get this to work, there's no way for me to get this finished in time which is really, really, really annoying.
  4. GPG


    Sep 18, 2015
    Any RF devices nearby and operating?
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