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I am planning to send data from a sensor to a mobile phone(such as iPhone) via mobile phone's trs connection(via audio jack). Since i have to use the audio channel, i need to convert the analogue signals to digital before sending to iPhone.

Does anybody have knowledge how can i achieve this in a simple way? What kind of micro controller and circuit components i should use?

I was planning to use Arduino as a micro controller. Some claims it happens by using FSK or Manchester encoding.

I need a simple schematics diagram for that, which i could not find.

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Why do you need to convert analogue signals to digital when audio input is analogue in the first place? Are you sure you don't want to convert digital signals to analogue? – AndrejaKo Apr 10 '12 at 18:25
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@cmd1024 It's not too late to go and accept those answers that were good. – David Kessner Apr 10 '12 at 19:32
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for example i want to use an ultrasonic sensor. i think i need fsk for that? the point is i want to make it with an atmel chip. since i already have arduino so i can program it. – cmd1024 Apr 10 '12 at 20:37
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You might actually be able to connect the pulse output of the ultrasonic sensor straight to the line-in of the iPhone. Then you'll just need to measure the pulse width on the iPhone. The point is that the iPhone inputs might have DC blocking capacitors, so slowly varying voltages won't get through, but the ultrasonic pulses might, – Rocketmagnet Apr 10 '12 at 20:47
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@cmd1024 Please edit your question with all relevant information. We shouldn't have to read through the comments to figure out what you are doing. Your approach should be, describe your problem in detail and explain what you have attempted to do and why you need our help. – Kellenjb Apr 10 '12 at 20:59
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1 Answer

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FSK (Frequency Shift Keying) is one option, though ASK (Amplitude Shift Keying) is easier. The reason why FSK is more popular is that it's less noise sensitive than ASK. Compare with FM and AM in radio transmission; FM also offers better quality. Since you want to transfer sensor data the required bandwidth might be low, and ASK may work satisfactory.

To generate ASK make an oscillator whose output level you can switch through a switchable voltage divider. To demodulate the signal a simple envelope detector

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followed by a comparator may be all you need. All depends on the required data bandwidth, which you don't mention in your question.

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I'm not quite sure how the demodulator would be possible to implement inside the iPhone. – Rocketmagnet Apr 11 '12 at 12:24

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