## Apple iPhone

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# Minimum input current an iPhone can detect via the 3.5mm jack?

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

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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.

Score 2

Thanks @oldturkey03, that's great info. Some follow up q's:

1. When you say the mic current will saturate at 40mV, does this mean that a potential of no more than 40mV can be transmitted from the mic to the iPhone?

2. I'm assuming if the resistance is greater than 1.6k ohms b/t the GRD and MIC, the iOS will switch to the external mic as well, correct?

3. After the iOS switches to the external mic, what's the minimum current that the iPhone can detect via the mic input?

1. yes from my understanding. 2. around 1600ohm's is correct. Somewhere the number is lower at around 850ohm. Try a couple of resistors of different values and see what your measurements come up to. . 3. really unsure of that since it really only works on the resistance. You'll have to measure that. The attached paper in the original answer may give you better information on that

@oldturkey03 Awesome, very helpful info. Thanks again!