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Audio induction coil

a.mlw.walker

Nov 15, 2011
39
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Nov 15, 2011
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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...
 

Timescope

Aug 30, 2012
43
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Aug 30, 2012
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43
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.
 

duke37

Jan 9, 2011
5,364
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Jan 9, 2011
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5,364
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.
 

a.mlw.walker

Nov 15, 2011
39
Joined
Nov 15, 2011
Messages
39
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...
 

duke37

Jan 9, 2011
5,364
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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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