arduinoaudioiphonevoltage measurement
I want to connect the output from the audio jack of an iPhone to an Arduino.
What voltage range can I expect to see on the audio lines from the iPhone? I assume that turning the volume up on the phone will produce a large AC voltage, but how large does it go up to?
I want to make sure that it wont exceed the voltage level that an Arduino can read on its input pins. Will I need to provide any circuitry between the iPhone and the Arduino?
Look into Project HiJack, which establishes 2 way serial connection to the iPhone via the earphone port and harvests power! The source code is open source.
They use Manchester encoding for modulation, a brief analysis of their code is on my blog.
Apparently you have a audio signal with 3.3 Volt peak to peak amplitude and want to couple that into a "microphone" input of some other audio device. Microphone inputs are meant to take the very small signals produced by microphones. These are often 1 mV or less, with peaks maybe a few mV in normal operation, although this depends a lot on the microphone.
For starters, you probably want to attenuate your input signal by at least 1000 in voltage. That may still be a bit high, but most microphone inputs can probably handle that. You will have to experiment. Maybe you need a attenuation of 3000 or 5000 so that you set the volume control near the middle of its range when listening. A simple start would be:
That will attenuate by about 2000 in voltage. Note the capacitor to AC couple the signal, which removes the DC bias of the input signal.
Best Answer
Commercial line out specification is to be able to drive 1 milliwatt to a 600 ohm load. For a sine wave, this means a voltage of 0.77 volts RMS (2.2 volts peak-to-peak) and a current of 1.3 milliamperes RMS (3.6 milliamperes peak-to-peak).