email(at)jaredyates.com
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 Posted: Sat Mar 14, 2015 6:54 am Post subject: Aviation Microphone Feeding Consumer Electronics |
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I've been tinkering with cutting apart one of these to integrate into my audio system in a modular way:
http://www.amazon.com/Streambot-Wireless-Bluetooth-Streaming-Receiver/dp/B00MJMV0GU
My plan is to put the circuit board into a little enclosure with a d-sub connector on the side, making the bluetooth module easy to replace if it dies or as improved models become available, as they seem to very often. Then the airplane wiring will have a mating dsub with leads for power (switched on/off at the panel), ground, outgoing audio to the airplane's audio system, and two leads for a panel-mounted push button switch that will replace the single push-button switch on the bluetooth device. That's all easy enough, but then I started thinking...
The main feature I'm after is the bluetooth audio, but this device also has phone call capability. It has a microphone that picks up ambient sound through the tiny hole in the case. While I'm in there doing surgery, could I remove the ambient microphone from the circuit board and connect wires where it used to be, and somehow link the headset microphone to the device?
I know there are headsets that have this feature built in, and and it may not be worth the trouble in the end- but one of the areas that I have least understood in the whole airplane is the audio system, so one of my goals in this investigation is to try and get a better understanding of how the system works.
I have several different candidates for audio input available.
First, there is the headset mic jack. Is there some way that I could attach wires to my headset mic jack at the panel, in parallel with the intercom inputs, and either directly or through some sort of circuitry, send those wires to the circuit board that is expecting to see a microphone? In this case, the outgoing call audio would only include what the corresponding headset mic picks up. If so, what kind of circuitry would I need to consider?
Next, there is the audio output that comes to the headset audio jack. The Flightcom intercom instructions say that I can make a 3.5mm "audio out" jack by putting a 47k ohm resistor in series with the headphone output. This is presumably the level of audio that a consumer electronic recording device is expecting to see. How does this kind of output compare to what the circuit board is expecting to see where the microphone used to be? In this case, the intercom audio would be going outbound on the call, so anyone who speaks in a headset is going to be heard by the call recipient.
Then, there is the output between the intercom and the aviation radio. This seems like the least likely candidate from an impedance standpoint, as I understand it.
Finally, one related question. Has anyone found a good way to isolate a 3.5mm audio jack from a conductive panel? Perhaps small insulating shoulder washers?
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