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Help Designing Light Airplane to Camcorder Adapter

Hi,

I'd like to use a camcorder in a light airplane, but I'd like the audio to come from the aircraft intercom system (which carries both radio traffic and crew conversations).

A typical light airplane has two jacks that you plug the headsets into. One jack is I believe for the speaker part of the headset, and the other jack is for the microphone.

So, I'm interested in interfacing from the "speaker" jack to a camcorder "mic" or "aux" input.

The two things I'm concerned about are:

a)Voltage differences in the signal.

b)Ground offset differences between the plane and the camcorder, particularly if (later) I use a power adapter for the camcorder, which would potentially link the ground reference of the plane with the ground reference of the camcorder.

I would normally think just a voltage divider with a potentiometer would be OK, but that doesn't cover the potential ground offset.

How do I findout what nominal voltage levels for airplane headsets and camcorder inputs are?

Any other suggestions?

Thanks, Dave.

P.S.--Nobody seems to make such a product. I did find one product that went inline with the microphone input of the headset, but that would only catch one person talking. I'm interested in recording everything that comes to the headsets, including radio traffic.

Reply to
David T. Ashley
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  1. I'm sure there are products to do this. I'll check for you. Recording the audio is not uncommon.
  2. You can isolate the grounds with either capacitors, or an audio transformer. The transformer idea might be useful as it can help with the issue of impedence mis-match.
  3. Leve shoudl be close if you use the cam-corder's line in jack. If you use the mic jack, I"m sure the level will be too high. Then a potentionometer or a fixed divider will work, IMHO.

I don't see any ground offset issues myself, I think you will find the headphone jack is referenced to ground, as is the camcorder's line in jack. Both are easy to check with a small meter.

Before connecting *anything* to the aircraft be sure you understand the implications of what you are doing. If you 'break' the communications system at teh wrong time, the result could be ugly--someone could be killed. Make sure there is an approved isolator panel in teh aircraft that you tie into--these serve to prevent anythign on one circuit from interfering with the other circuit(s).

Reply to
PeterD

After I made the post, I did find the PA-80S here:

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Seems to be the right thing. The company has advised me it goes to the LINE jack.

The audio transformer seems like the right idea. It provides total isolation, whereas the cap approach requires that one wire be connected directly between the jack and the camcorder.

In practice, I'm going to use the proven solution from the company cited above (or, if you find other products, one that you suggest). This should minimize the risk of home-brew circuits.

Thanks for your help, Dave.

Reply to
David T. Ashley

I think you've made the best choice! Good luck with it.

Reply to
PeterD

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