Intercom

Sounds like a problem you'd also have in this vehicle:

I politely declined a second ride. The 'helmets' have a headset which you plug into the vehicle's intercom system which is (presumably) basically a summing amplifier. All microphone signals get mixed and send to the earpieces. You can do the users a favor and implement a push-to-talk switch. If you use quick-disconnect connectors -which are specifically designed for people who forget to unplug their headset before walking away- almost nothing can go wrong. I wouldn't go for RF or optical because that also means the use of batteries.

Think motorcycle intercom with bluetooth. BT can do up to 8 piconet nodes.

see:

as an example.

That's what we do.

Oh, now come the *hard* specs to meet. ;-)

One of the big problems with any digital system is going to be echo. There are essentially two sources of it, the return of your audio to you form the summing of all audio and "acoustical echo" caused by your voice getting into another's open mic. The first can be helped quite a bit with a decent hybrid circuit and echo cancellation software. It's a little tricky, but not too bad. Accoustical echo is very difficult to get rid of, once it's in the system. Setting the gains of the mics properly and shutting off mics when the headsets are removed helps.

The guys at Snap showed us a demo of their unit doing some pretty neat digital audio. Just the radios will be pushing your $100 limit but everything else is pretty simple for their system.

That just uses some cheap CHinese motorcycle ready-made parts. I was sort of hoping that somebody had messed around with some of the cheap chips that were on the market so that I could proceed with my own design.

Thanks,

Jim

Get a military headset, used in tanks, etc. They use a differential microphone, where sound coming form some distance, cancels out, and your voice(close by) does not cancel. Works in awfully noisy environments .

Right. But even the cheap Chinese device will not meet your $100 for all four people. A good set of headphones that are conformable to wear for any length of time are going to bust your budget for the first pair. Plus, even with the Chinese radios you will still need to do some software and design to build the piconet to four or more devices.

Good luck, tm

My customer already has a headset, complete with noise cancelling microphone, standardized plugs and all that. I simply want to make a box (up to 4 boxes per vehicle) that (s)he can plug their headset into and intercommunicate with the other passengers.

My envision, perhaps a little foggy, is a transceiver inside the headset and a 4-channel receiver mounted as a master unit elsewhere in the vehicle rebroadcasting on the 4 channels.

I can't be the first person in the world that has wanted to do this. I don't think so, anyway.

Jim

Method 1:

The cheapest method I could think of boils down to this but it's only if you design a mass product: Each headset gets a super simple transceiver. They all receive on the same frequency but transmit on different ones. The car has a central pod that receives all those, adds (maybe with a "sneeze muffler") and re-transmits the summed audio on the common frequency.

Since they are all in the same vehicle it doesn't need any range and whether AM or FM can be determined by whatever costs three cents less. You have to think super-cheap consumer gear when developing the circuitry. No fancy chips. If you want to go fancy and save time:

But ask SiLabs first if you can get them. This is boutiques stuff, most seem to roll their own so there isn't much of a market.

Method two:

Get four DECT phones where you are sure the base can work with a 12V supply. Also, make sure that multiple intercom is possible, meaning more than two handsets can participate. Now that won't be Hifi but I've bought a set with base and three handsets for around $80 a while ago. Good thing: Now you've got range. The guy going into the burger joint can keep his headset on and can ask "Yo, Jim, you wanted fries with you burger, right?" :-)

Check Fair Radio Sales for a tank interphone amplifier.

I've always thought it would be cool if drivers in cars could talk with drivers of other cars in close range. "After you, red Beetle, please" is the (optimistic) idea.

I was thinking that the audio could random-pulse-density modulate an AM carrier, so a fair number of players could be sending at the same time and everybody would hear. Some sort of voice actuation would be necessary at each transmitter, to keep the noise level down. Digital packet ideas might work better, but simple analog pulse density is, well, simple.

PAM (pulse amplitude modulation) is a possibility, too. That would make volume fade with distance, sort of like being in a room with real people.

John

Go to your nearest airport that has an FBO, and start pricing intercom systems.

Or check Wicks or Aircraft Spruce and Specialties and see what they have.

Excuse me, but am the founder of my local FBO. I've been in competition with Wicks, Spruce, and a few dozen more for 35 years. I'm trying to beat them at their own game. I do avionics design for a living and have for nearly 50 years.

Would you teach your grandmother how to suck eggs?

Thanks

Jim

You can do better than that, Don. I know you can.

Thanks,

Jim

On a sunny day (Mon, 08 Aug 2011 17:21:32 -0700) it happened John Larkin wrote in :

Existed for many years, called CB,

Squelch, push switch on mike, channel switch on mike, scan mode.

I have 2 such units, one a very powerful one. These day we have AM, FM and SSB allowed here.

The idea I had was for simultaneous conversation, like people being in a room together. It's not realistic, but the modulation concepts are interesting.

John

On a sunny day (Tue, 09 Aug 2011 08:31:43 -0700) it happened John Larkin wrote in :

hmm, I was thinking - have you ever seen that movie: "The Blues Brothers' where they drive around with the huge speaker on top of the car.... hehe :-)

Go to your local airport or airplane store and ask how they do aircraft headsets.

If the people were allowed to plug their headsets in somewhere it could be done virtually for pennies. (well, probably significantly less than $100.00).

Good Luck! Rich

Huge speakers are a good idea.

John

Well, if you've already got headsets that plug in, then your biggest expense would be stringing wires through the car. Then a summing amp under the dash or behind the back seat, distributed to everybody.

Even if you used walkie-talkie guts, if you don't want to go through a battery every day or so, you'd need to string some wires anyway.

Good Luck! Rich