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Bluetooth ISM interference problem

Discussion in 'Radio and Wireless' started by sirch, Jun 28, 2013.

  1. sirch

    sirch

    109
    1
    Dec 6, 2012
    I have a project that uses an RF Solutions ISM module - http://www.rfsolutions.co.uk/acatalog/info_FM_RRFQ1_433P.html which works well.

    I added a Bluetooth module to the project similar to this one http://r.ebay.com/3MNeiS and I get a load of interference that stops the project working.

    As can be seen from that attached image everything is mounted on a piece of stripboard and in accordance with RF Solutions the radio module is mounted above the board on short wires.

    The question is: does anyone have any recommendations for getting rid of the interference between the bluetooth and the ISM module e.g. screening, low pass filter etc. What is best and how to implement it?
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,327
    1,769
    Sep 5, 2009
    hi there

    well I see 2 major problems, both are in your layout

    firstly you have no shielding between the 2 modules
    secondly you have the data and power lines passing right under the 433 module

    Im not suprised you are having interference problems
    I would be moving the 433MHz module way down the board further to get some separation and also even then if needed putting a grounded metal shield ( wall) between the 2 RF modules

    Dave
     
  3. sirch

    sirch

    109
    1
    Dec 6, 2012
    Thanks for the reply. I have tried various things and done more investigations and it turns out to be nothing to do with either the bluetooth modules or the radio module!

    The serial output from the Arduino module is interfering with the ultrasonic receiver circuit, attached. If I put a 100nF capacitor as shown in red on the circuit diagram it kills most of the noise but the circuit barely works (no big surprise I guess), smaller caps don't make much difference. I only see the noise when the serial lines on the Arduino are loaded, no connection, no noise.

    The question now is, is there anything better I can do other than putting the whole ultrasonic receiver circuit in a can? Would a screened serial connection help? (you are probably yelling YES at this point but the reason I have not done this is that I want to use bluetooth so essentially it would be a short screened cable to the bluetooth unit at which point it is exposed again.)

    In general are there any tips for tracking down and fixing interference of this type?
     

    Attached Files:

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