Help needed with audio to video camera in aircraft

I want to do some video work out of the airplane. I need to use the cameras audio input to isolate the built in speaker which is worthless. I would like the camera to hear everything that I hear and say in my headset - intercom, radios, etc.

As I understand it the David Clark's are not compatible with the camera so I would like a "magic box" I can plug my headset into and it into the airplane as usual. The box would have an audio output that I can plug into my camera. I could then use the box in different airplanes.

I can build it but do not have a clue how to design it ... needs to be simple!

HELP! and thanks so much.

Rexlan said:

I want to do some video work out of the airplane. I need to use the cameras audio input to isolate the built in speaker which is worthless.

Click to expand...

Do you mean "speaker" or "microphone"?

Rexlan said:

I would like the camera to hear everything that I hear and say in my headset - intercom, radios, etc.

As I understand it the David Clark's are not compatible with the camera so I would like a "magic box" I can plug my headset into and it into the airplane as usual. The box would have an audio output that I can plug into my camera. I could then use the box in different airplanes.

I can build it but do not have a clue how to design it ... needs to be simple!

HELP! and thanks so much.

Click to expand...

Look up the specs on your video camera to see what voltage level the Line audio Input expects. Also see if they specify the input impedance? mono or stereo?

Can you scrounge a small audio 500Ω/500Ω or 600Ω/600Ω coupling transformer like this one?

I though of another question: Does the airplane(s) you normally fly have rear seat jacks that are normally not used? (like when you fly with an instructor with no passengers)?

Both of my aircraft have a built-in four-place intercom with rear seat jacks. If I wanted to record what was happening on the comm radios and the intercom chatter, I would plug the recorder into one of the rear seat headphone jacks and not mess with my front seat jacks or headphones. Unless the intercom is switched to the "Pilot/Crew Isolate Mode", the rear seat jacks are simply wired in parallel with the front seat jacks, eliminating the need to make a plug box that you plug your headset into.

OK ... got the info I think. I will be changing to a different HUD camera someplace down the line so it is desirable that the "magic box" be as generic as possible. I don't know if these video cameras are all about the same as far as external Mic audio inputs.

My current camera spec says
Audio in = 327mv
Input impedance = 47K
Output impedance = 2.2K

The current airplane has 4 position jacks; however, my Super Cub does not. I could however, put another jack in the Cub if needed and that is fairly simple.

I can order that transformer I suspect if it is needed. I don't have anything on hand. I have almost any resistor or cap, diodes, etc on hand.

I see Radio Shack has this one:
1:1 Transformer

Rex

Here is what I recommend: Use a Stereo Plug, required if your aircraft is wired for a stereo entertainment system. Using the isolation transformer prevents a ground-loop if you are powering the camcorder from the aircraft's electrical system, and prevents overloading the existing headphone amplifier.

The Pot will let you set the recording level. The output is bridged to both right and left channels.

Great and that looks simple enough.

Question .... I will always power the camera via battery and not from the AC system. Is it possible to eliminate the transformer? My thinking is that if I can uses only a few resistors that I can probably put them in the connector plastic barrel and make a really clean setup.

Thanks

Try hooking sleeve to sleeve; top of 1K Pot to Headphone Plug Tip. Bottom of Pot to the Sleeve/Shield connection.

More clarification:

You show a 1/4" stereo headphone plug which I'm sure I can find. Can I also use a standard AC headphone plug and what rings would I connect to on it?

Is there a possibility of eliminating the 1K pot? Realistically I don't know if I can set it. Do you have a best guess for 2 resistors to replace it ... or just one?

I am going to try for the transformer first because it would isolate the unit as you said and make it fail safe to the AC system. I may even do that if I need to use a small handy box just to be safe.

The voltage level at the headphone jack (across the other headphones, i.e. pilot and copilot), is about 2vp-p. Your Camcorder wants about 0.3V (dunno it that is rms or p-p?), so you need an attenuation of about 1:8. That is what the pot will do. You will be able to set the level as required. Presumably, there is some sort of VU meter, led or something to know if the audio level during recording is correct. I suggest starting with the Pot, and then after determining where it needs to be set, remove it, measure the resistance above the wiper, and below the wiper, and substitute two fixed resistors.

Headphone plugs on aircraft headsets are standard 1/4" plugs like you can buy at RatShack. Mic plugs are special. If you plug a mono (no ring) jack into an aircraft wired for stereo, you will short out one channel of the audio. I have had to cut off mono plugs on commercial headsets (David Clark), and replace them with a Stereo Plug just to avoid the short circuit. Modern headsets come pre-wired with stereo (tip, ring, sleeve) plug, and usually have a mono-stereo switch on the headset...

If wiring a mono device to a stereo plug, hook up only the tip and sleeve; no connection to the ring.

Thanks very much ... I think I've got it now. I've still got the older David Clark headsets ... looking at a Light Speed!

Rex