Bluetooth noise

Discussion in 'Wireless & RF Design' started by jimmyho08, Apr 15, 2014.

  1. jimmyho08

    Thread Starter New Member

    Oct 7, 2013
    16
    0
    I recently bought the RN52 bluetooth module from Microchip. I am trying to implement this module for a product which just draws the audio, and then amplifies it to a speaker.

    I have ran into a problem. I have connected the analog ground of the bluetooth module to the analog ground of my product, and the other grounds to my digital ground. However, when the bluetooth module powers up, and the minute you pair with it, it produces this high pitched noise on the audio line.

    The noise goes away when you play music, and then when you pause the music, after about 5 seconds the high pitched sound is there again for about 15 seconds before the bluetooth module goes into I guess a sleep mode since no music is streaming.

    I assume this is either because of ground noise or power noise. When I probed the 3.3v line there is this terrible noise on the line.

    Because I did another test. Using an external speaker(has internal amp inside, and powered by a power cord). I just powered the bluetooth module with the bench power supply with 3.3V. And then connecting an RCA cable to the external speaker, and cutting it, I connected the audio line, and analog ground to this wire, and the music plays great. No high pitched noise.

    I have attached a picture of the noise I am experiencing from the 3.3V line.
     
  2. PRFGADGET

    Active Member

    Aug 8, 2011
    51
    7
    Since we can not see exactly what you are working with, I will offer a couple of old basic thought's.

    1. Try a 1:1 600 ohm isolation transformer in the line between the audio out and the bluetooth input .
    2. Try coupling or DE-coupling capacitors in the audio line.

    You seem to have a "Ground Loop" situation, even a combination of the above might be in order to re-leave the problem .
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    is the bluetooth reciever a super regenerative type? with superregens, if you get two too close together, they can redieve each others noise. the regen and superregen are the simpliest recievers with sensitivity and have the lowest part count, therefore, they are popular.
    the noise from a supre regen reciever looks like white noise when not recieving a signal, and quiets when recieving.
     
    Last edited: Apr 30, 2014
  4. DrRich

    New Member

    Apr 21, 2014
    5
    9
    Not sure what you are doing entirely, but try decoupling your bluetooth module as PRFGADGET suggested. If it was me I would place a 100nF capacitor as close to each power pin as possible, and perhaps even have a local larger cap say 10uF to 47uF fairly close.

    Back when I was a student I had terrible problems with powering a Telit GPS/GSM module (due to my bad PCB design :rolleyes:). Not sure about bluetooth modules, but FPGAs and GPS/GSM modules can have quite high peak current demands.

    This document is a good read for reducing emitted and induced noise:
    http://www.ti.com/lit/an/szza009/szza009.pdf
     
Loading...