I bought one of those cheap cup-anemometers that you can stick into the 3.5mm headphone jack of an iPhone or Android device. I'm assuming it is some sort of pulse generator and that the app uses an audio library of some sort to count and time the pulses. I want to hook the thing up to an oscilloscope and see what it outputs so that I can eventually hook it up to a Raspberry PI or C.H.I.P board computer. Since I don't want to fry the thing and I'm not really very good with electronics I figured it might be a good idea to ask what the microphone output voltage of, say, an iPhone is?

enter image description here

I'm assuming that all I have to do is simply connect N Volts to the 'Mic' part of the 3,5mm jack on the anemometer and connect the 'Ground' section of the 3,5mm jack to Ground on the scope and then observe the output with an oscilloscope?

So N=?

  • \$\begingroup\$ "microphone output voltage of, say, an iPhone is" There is no microphone output from an iPhone. Do you mean input? \$\endgroup\$
    – winny
    Commented Oct 21, 2016 at 14:24

1 Answer 1


Taking the Android specifications, you need 2.2Volts in series with a 2.2K resistor.

Like this example from the Android specs:

enter image description here

You can probably use 3V (2 AA Cells of 1.5V each.) 5Volts through that 2.2K probably won't hurt anything either.

Example for using Scope:


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ If you use a higher voltage, also use a higher series resistance. \$\endgroup\$
    – Ben Voigt
    Commented Oct 21, 2016 at 14:39
  • \$\begingroup\$ I read something about the output voltage on the iPhone being 2.8V so that sounds likely and thanks for the diagram. I'm so bad at electronics one literally has to draw me a picture. So I connect: 2.2V -> [R=2.2k Ohm]->(Mic)->(Veq)->GND \$\endgroup\$
    – os x nerd
    Commented Oct 21, 2016 at 14:59
  • \$\begingroup\$ @osxnerd: Circuit diagrams are clearer than words when discussing electronics. \$\endgroup\$
    – JRE
    Commented Oct 21, 2016 at 15:00
  • \$\begingroup\$ What exactly is Veq? \$\endgroup\$
    – os x nerd
    Commented Oct 21, 2016 at 15:02
  • \$\begingroup\$ Not needed for what you are doing. Veq is the DC voltage when one of the buttons is pressed. The mic input on the Android device also goes to an ADC that reads the DC level. Depending on the DC level, the device can tell which button on a headset with wired remote control has been pressed. \$\endgroup\$
    – JRE
    Commented Oct 21, 2016 at 15:05

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