Frequency Shift Keying

從iPhone到Arduino的，你可以從阿爾杜伊諾到iPhone發送數據。通訊速率為1225bps（實際數據傳輸速率※是有點低）。它適用於少量的數據通信的諸如傳感器的信息和切換輸入。
請使用4針微型插孔（L / R / GND / MIC）的電纜連接到iPhone。常見的立體聲電纜，以便3極迷你插孔（L / R / GND），給我你的。串擾是由電纜產生的，它可能會導致通信錯誤。建議採用鍍金端子屏蔽電纜。電纜的長度是一個很好的短。

FSK Modem

Example circuit in Japanese.
https://code.google.com/p/arms22/wiki/SoftModemBreakoutBoard

iOS framework and Ardunio solution (code):
https://github.com/jensmeder/FSKModem
https://github.com/ezefranca/FSK-Arduino-iOS

Android sample code:
https://github.com/hitesh24by365/AudioJackTransfer
https://github.com/cytecbg/android-fskmodem

Androino:
https://code.google.com/p/androino/

Smart phone with real voice demo:
https://www.youtube.com/watch?v=kb_e3DPPdsU



FSK or similar modulated-audio communication via audio-jack (no MFi needed)

You would have to implement hardware FSK modem on the RPi side and a software one on the iOS side. It is a bit tricky but by no means impossible.

Of course you could implement software modem on the RPi side, too. But since RPi doesn't have audio input you would have to use an USB audio card or something. Or complicate your life trying to sample an analog pin fast enough.