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Audio induction coil

Discussion in 'Audio' started by a.mlw.walker, Nov 17, 2012.

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  1. a.mlw.walker

    a.mlw.walker

    39
    0
    Nov 15, 2011
    Hi guys,
    wasnt sure where to ask this, so went for General...
    I am outputting pcm audio data through a pwm pin of an ATMega1284, with an RC circuit and a 3.5mm jack I can hear the audio through headphones.
    I want to replace that with an induction loop like the hearing aids use or one of these (the loop bit)
    http://www.spyearpiece.co.uk/produc...packages-bluetooth/spy-earpiece-bluetooth-kit

    I was reading people have done it from their hifi's, with loops around their sofa's, but I wasnt sure of the actualy "science" required to do this. I assume for distance, I need reasonable voltage (powering avr from 3.3 volts currently), and perhaps an op amp.
    Anyone got a circuit or something they could suggest, I was gonna try with just a loop of wire, but I think I need to match the impedence, but Im not sure what to match it to...
     
  2. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    The item you referred to uses Bluetooth technology which is a wireless transmission system operating in the 2.4GHz band. You can do a google search for bluetooth kits for home audio.
    Timescope.
     
  3. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Audio loops for deaf aids use quite a large current. The bigger the loop, the larger the current requied.

    The current can be reduced if multiple turns are used and this is often used to get a resistance nearer to the load required by the amplifier. An approximate current drive can be made by using a higher voltage and a series resistance. Proper loop drivers use current negative feedback.

    It is many years since I played with this but there were details of the field strength required on the net.
     
  4. a.mlw.walker

    a.mlw.walker

    39
    0
    Nov 15, 2011
    induction loop

    Timescope, I think you need to look again - bluetooth is used to send the data to the unit I posted, but then an induction loop is used to transmit the audio to the earpiece - it is this I am trying to replicate. I know what bluetooth is, and there are many bluetooth modules on the market.

    Thanks Duke, thats a bit more like what I was after...
     
  5. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    Thanks for the explanation.

    Timescope
     
  6. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Wikipedia has a page on audio induction loops and refers to a British Standard which can be used to design a loop. It can be simple and crude or complex and expensive.

    You will need a device with a pick-up coil and an amplifier - maybe a scrap hearing aid will do.
     
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