Intercom

Looks like you're trying to reinvent exactly the system used on basically every helicopter ever flown.

I see no particularly good reason for doing _that_ wirelessly. Those headsets are needed in that vehicle, and only in there. So they should be part of the vehicle itself. Which is why they _should_ be attached to it by wires.

There are many such wireless headsets already. They're particularly popular in aviation, as well as in noisy applications (like fire engines, railroads, even for use on motorcycles). The simplest designs use a single wireless headset which attaches to a standard aircraft intercom system via an adapter to plug into the intercom port (and then you can have as many headsets as you have intercom ports). Note that electronically most small aircraft intercom systems are pretty simple. Adapters that convert a standard wired headset to Bluetooth also exist. More sophisticated units integrate the (usually) Bluetooth host module into the intercom system, so you don't have little adapters all over the place (and fewer batteries to keep charged). There are far too many to list, but Google for "wireless aircraft headsets" or "wireless aircraft intercom".

The aviation gear is typically pricey, but many of those manufacturers sell non-aviation versions as well.

I also previously responded to the OP that the best way to reduce environmental acoustic noises (engines and generators) is sampling the background, bandpass the frequency (usually 50Hz to 100Hz), phase shift 180 the filtered signals, amplify and inject it back into the environment. You might not even need the headphones.

I am working on a system for a noisy generator.

Search for motorcycle wireless|bluetooth intercom. (Not sure they support four stations.)

-- Roberto Waltman

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There may be a way to adapt the avcomm wireless headset to an intercom and have all the crew be able to communicate - not sure;

t_id=3D68

As others have suggested there are many existing types of wireless intercom systems. Here is one that is specifically sold as a 4-person wireless system.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com

I respectfully disagree, sir. I have been working on aircraft of all shapes and sizes, including helicopters,for over 50 years and can assure you that every helicopter does NOT have exactly this system.

And, every helicopter I've ever worked on has the headsets on a plug for removal if desired.

Thanks,

Jim

You'd think so, wouldn't you. My field is aviation and I think I've seen as many aircraft as any other mechanic/engineer. As yet I haven't seen any light single engine aircraft fitted with one.

Most of them cost nearly an AMU (Aviation Monetary Unit, generally accepted value is $1000) and are meant for heavy iron, not light singles.

I should have been more explicit. I'm trying to do it for less than $150 for all four stations, headsets not included because nearly EVERYBODY has a set of mickey ears already.

Thanks,

Jim

And I tried to tell you that there are a dozen manufacturers who sell exactly that kind of headset, right from Bose through Telex to some offshore products. They all work well to some degree. I have absolutely no interest in getting back into the aviation headset manufacturing business ... been there, done that, got the t-shirt and am negotiating the movie rights. Aviation headset business is absolutely cut-throat.

Thanks,

Jim

I'm not looking for a product; I'm looking to get educated on short-range communications technologies and component selection.

Thanks,

Jim

Too expensive by about a factor of 5 and a crystal bitch to install. Once again, I do NOT want a headset product.

Thanks,

Jim

About a factor of 5 too expensive and completely incompatible with the rest of the environment it is going into.

I'm really looking for chip and systems information and education.

THanks,

Jim

Well, there's bluetooth, zigbee, um, I suppose a system might be made to work with infra-red.. Possibly the civilian walkie-talkie band.

Maybe something like these from Nordic (although relying on a single manufacturer has obvious vulnerabilities). Sparkfun has breakout/dev boards with the chip for about US$20. Multi-user could perhaps (I've not played with these specific chips) be implemented with a token-passing scheme: he who speaks first gets the floor (air) and then the token goes round-robin until somebody starts talking. Data rate seems good enough for decent speech quality.

--
Rich Webb     Norfolk, VA

And I can't find any hard data that lets me go into learner mode for either of them, noradvice on any supplier of the parts that is better than the other.

um, I suppose a system might be made

Tried it. nobody can guarantee the orientation of any of the other headsets during the fliight.

.. Possibly the civilian walkie-talkie band.

Even better ... either the top of the 6-meter ham band or somewhere in the 220 band. I know each person should have their own ham license for this to work, but I can also rely on the section of Part 97 that allows ONE licensed person to allow nonlicensed persons to operate the station if the licensee is capable of controlling the emissions.

Besides, we are talking a few milliwatts here and that range isn't going to be measured in thousands of feet. I'd venture a guess that two metal aircraft flying in formation wouldn't be able to hear anything from one ship to the other.

I thought perhaps there was a cheap easy digital way to do it, but it looks like I'm back to the same old FM superhet. At least if I do it in the ham bands I don't have to go through Part 15 certification to do it.

maybe take a l,ook at how these are imp[plemented;

allows internal conferencing for up to 5 people;

no base station - each beltpack allows 4 other stations;

I suppose 4 cellphones could also conference call each other......

Look into a set of 4 COTS BT earpieces for cell phones. Pair each of them with a "box" that you design. *In* that box, you receive on each of N (n=4) input channels, mix the signals (digitally) and rebroadcast on all N output channels.

At least, *conceptually*.

In practice, you would probably want to attenuate Channel X's *input* when rebroadcasting it on channel X's *output* (think: sidetone).

The bigger problem is noise cancellation (if ambient noise levels are

*that* high). Here, you might be able to exploit the fact that all N users are in *roughly* the same acoustic environment (?). So, the "inputs" from those N microphones will have some common audio signal that represents "ambient noise". You could identify this and "subtract" it from the signal that you route to the N *outputs*.

Finally, these (inexpensive) earpieces tend to only fit in a single ear (there are "stereo" headsets available but fewer and for more money). So, the other ear is still exposed to the environment. Ear plugs?? :>

Note that the earpieces are small, lightweight, commercially available, etc. The "mixer box" isn't as heavily constrained in terms of resources (because it stays with the vehicle, not the occupants!)

HTH

The amount of work is the same, whether you cancel it internally or externally. You still need to sample, phase shift and amp the signals.

this

Take a look at purepath of TI.. imight be interesting for your application...

Cya

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