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I want to build a relay circuit that turns on an external microphone (powered by an internal 9V battery) when a connected camera is turned on (a camera offering only 1V plugin power through a 3.5 mm jack: Panasonic GH4). Hence, the circuit (that can be easily powered by the 9V mic battery if needs be) has to "wake up" the mic when it detects the 1V —sorry if this sounds vague, but I'm no engineer: a friend promised to build it for me if I provide him with the schematics.

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    \$\begingroup\$ How much current can the 1V source supply? Regardless, a MOSFET with Vgs(th) below, say, 750mV ought to work. \$\endgroup\$ – uint128_t Mar 28 '16 at 1:47
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    \$\begingroup\$ Does the microphone audio connect to the camera via that same plugin power 3.5mm jack? \$\endgroup\$ – Dwayne Reid Mar 28 '16 at 2:09
  • \$\begingroup\$ I'm having a hard time figuring out the current that the camera can safely supply. Specs are vague as in all consumer equipment. But according to Wikipedia (en.wikipedia.org/wiki/Phantom_power#cite_note-14) camera abides by Plug-in-Power (PiP) specs as defined in IEC 61938 so it's 3V to 5V and not 1V as I previously stated. Voltage that is provided through the same 3.5mm connector (see Wikipedia article above—at PiP—for a more detailed description). \$\endgroup\$ – simone Mar 28 '16 at 3:15
  • \$\begingroup\$ Too bad that IEC 61938 is behind a paywall: the specs are all there (at page 20, according to the preview index). \$\endgroup\$ – simone Mar 28 '16 at 4:59
  • \$\begingroup\$ @Dwayne Electret mic capsules can be powered directly by DC bias from a 3.5mm jack. The DC power is fed typically through a 2.2K resistor, and a capacitor blocks the DC from the mic preamp input: prosoundweb.com/images/uploads/AAPSWPhantomPowerFigure7.jpg \$\endgroup\$ – simone Mar 28 '16 at 14:59

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