Wire Line-In and Microphone to Same Jack?

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lerxstrulz

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Hey All,

Just wondering if wiring the positive side of Line-In and Microphone to the same lug on a 3.5mm jack and then just wiring either the ground of the Line-In or Microphone to the ground lug would cause any problems. I have an app where users can choose between microphone or line-in, and previously was wiring to separate jacks and was wondering if I could save space by connecting both to the same jack. I did a quick prototype and so far have not noticed any issues other than a non-powered microphone now works when line-in is selected (previously would not.)

Thank you!
 
Note, many of the common 3.5mm breadboard jacks have 5 wires. The middle pin is ground and the outer two pins are meant for the left and right signals and the inner two pins are meant for line-in left and right signals. If you plug a microphone into the jack, it will not connect the line-in pins. If you take out the microphone jack, it will connect the line-in pins. Here is the Adafruit version of the jack:
 
Yes, you can plug both a line-level source and a mic source into the same jack when a mic preamp is present. This is exactly how the XLR inputs on an audio mixer work. When you plug in a line level source, you simply set the mic gain to 0db. Dedicated line-inputs on audio equipment do not have a preamp and that's why you can't use mics in dedicated line-in jacks. But you can always plug line-level into mic jacks as long as your turn the gain down.

The jack Michael is speaking of still requires two separate jacks. The idea is when nothing is plugged into the 3.5mm jack, the normaling contacts connect an external circuit to the jacks 'output', and when you plug in something, it disconnects this 'external' source and connects what is now plugged into the 3.5mm jack itself.
 
Thanks for the replies. I ended up just wiring it to the mic jack for both types of inputs. I noticed with the L/R lugs wired to both line-in and mic with a common ground there was signal loss and I didn't want to risk damage. Even though the input for the Audio Adaptor was set to either line-in or microphone, it seemed like both where always working because the normal wired mic would work while the input type on the board was set to line-in, and previously it would not if they were wired separately. I was thinking that if I connected the L/R lugs on the 3.5mm jack to both microphone and line-in inputs, one or the other would turn off if I selected line-in or mic as the input type for the Audio Adaptor.
 
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