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I’m creating an external accessory that will plug into the 3.5mm jack. As such, I’m wondering what the minimum current the iPhone can detect via the mic input? I’m determining whether I need an opamp to amplify my 25uA-500uA current that’s produced by the device. Thanks! Ali
The iPhone as well as other mobiles will apply a DC voltage about 1.5-2.5V to the microphone. The impedance of the standard Apple miniature hands-free microphone, is about 1600 Ohms. This means, if you simply connect a 1.6K resistor between the MIC and GND connections of the TRRS connector, the iOS will switch to the external microphone. The microphone input of the iPhone will saturate at about 40 mV peak (millivolts). The current for the mic is likely to be pretty small, less than a mA. For more information read ==» kuo10hijack.pdf«==this paper. Great information comes from all over thissite.
