Stereo intercom for my experimental airplane

[mnvelocitypilot]

I'm in the process of getting a really nice experimental Long-ez airplane back in the air that hasn't flown for at least 15 years. One of the things I need to do is to replace the intercom, and I'd like to "roll my own"...

I ought to be capable of doing this - I'm a EE with lots of bench experience. I just need a place to start - and I'd MUCH appreciate any help!

Here are the requirements:
- 2 seats (i.e., two headsets each with a boom mike)
- 2 communications radio inputs (mono), and 1 stereo music input
- Separate transmit "key" required for pilot & passenger
- Automatic squelch preferred, manual if absolutely necessary
- Panel space is quite limited on this airplane - i.e., small is beautiful.
- Proper design for noise immunity
- 12V

So... this looks to me to be a fun project, and, as I live in Minnesota where winters are long, I need a good project.

Does anyone out there have any good ideas?

THANK YOU!!!

 

[Fenris]

To start, what are your headsets? Specifically, what is their impedance, sensitivity, stereo/mono, and microphone type?

Otherwise, this is a fairly straightforward mixer/headphone type implementation. It's probably best done with SMT op-amps. What are your panel size constraints exactly? It looks like there's going to be alot of volume control knobs.

 

[6L6]

Honestly, just buy a non-TSO PS engineering audio panel. They have all the intercom built-in.

BUT, as you have a big panel expenditure coming soon for ADS-B, making your own is interesting. Make a block diagram of all the inputs, outputs, level controls, switched, buffers, etc... and go from there.

 

[mnvelocitypilot]

Thanks, Fenris - I've got a few different headsets, both bose noise cancelling and Telex. I'll likely use the Telex in the new airplane and leave the Bose in the old. The Telex headsets are stereo, 4 ohm, and have electret mics.

Typical aircraft intercoms only have one volume control. The audio from each receiver is line level (100mv?), and is adjusted with the volume control on the radio it's from. So what we're really talking about is a multi-input mixer, potentially with automatic squelch on each channel.

AFA panel constraints, the bottom line is that smaller is better, very small is a requirement, and NO panel space required is best (although a volume control will be required).

Hi 6L6, and thanks for responding! I've got an old drawer filled with tubes... I'll bet there are some 6L6's down there! Anyway, yes, there are many non-TSO'd audio panels out there, and PS Engineering makes a fine one... that's actually what I've got in the Velocity. I was actually looking for a project as I like "hand rolling" stuff if I can (which is why I build airplanes!). I'm pretty familiar with the market. If I wind up buying an "off the shelf" model, it turns out Dynon now makes a pretty good, pretty cheap intercom system for around $250. It just seemed like it'd be fun to build my own.

Thanks again to both!
Dave

 

[djn]

Cool Dave. I didn't want to go high tech back then so I built and flew a Cassutt M111. Two of my friends built Long-EZs. Very nice plane. Good luck.

 

[6L6]

Dave, you say "replace the intercom", which begs the question, what's it got now?

 

[wayne]

I put the PS7000 in my plane I couldn't justify the time and expense of doing my own. It is also TSO approved since the plane is certified. The PS is very nice.