I'm building an intercom (none of the off the shelf ones do what I want without costing silly money)....

I'm trying to decide whether to make it so that when I speak I hear what I'm saying through my own headphones. Not sure what the professional ones do!!

Cheers for any opinions... When the things finished I'm going to put up a schematic... Just waiting for my bro to give me back my handheld oscilloscope so I can do some work on the mobile phone attachment bit....

I voted for the last option, based on long-distant memories of telephone theory - humans need a bit of feedback of their own voice, otherwise they tend to talk too loud. If the feedback's too loud, the people tend to talk too quietly!

That's what I was thinking
Also, it'll give some feedback about when the squelch has gone wrong!!!

I have intercoms on my helmets, sitting one behind the other with helmets on would otherwise involve some very loud shouting! You hera your own voice thro' the headset when you speak, probably for the reasons mentioned above.
I also fly light aircraft & the headsets used do exactly the same on those too.HTH
Be interested to see your final plan as I agree that nothing cheap seems to cover all the options.

You need your voice to be mixed into the earphone otherwise it's very hard to use. Mobile/landline telephones have to do this and there's been lots of research in the area on how much you need. I'd stick a preset on the PCB and tune it while using. Also be careful of absolute silence, mobiles mix in a little (I think pink) noise during quiet bits of conversation. The human sensory system is a more complex beast than most suspect.

Yes- I was just thinking that if I put a pot on the PCB, depending on the result of the poll and having a fiddle with the board I could having anything between 0% and 100%....

Hopefully silence won't be a problem- the mp3 player input gets attenuated (but not silenced) during speech but not stopped totally so there should be some noise.... Didn't know they did the pink noise stuff though!! Interesting I suppose it's to let you know the line hasn't gone dead??

My Starcom set has the option of no feedback or full. I tried with none to start with and it was impossible to know how loud to speak. Since then I've switched the feedback on and it's much nicer to use.

[Edited on 1/10/07 by matt_claydon]

I recently went up in my brother's light aircraft this summer. We both had Peltor headsets with a voice-operated intercom. As the cockpit was VERY noisy the microphones were voice-switched, which would be the situation in an open Locost - not engine noise, but wind noise.

I found them quite hard to use, due to the slight lag in turning on after starting to speak. Ended up having to start every time with "er..." or "ah..."!

The other problem I have with cheap commercial intercoms like the Maplin one is that they use earpieces like the ones you get with MP3 players, and I can't keep them in my ears. I keep meaning to replace them with a small speaker next to my ear, but haven't got round to it yet.


David

[Edited on 1/10/07 by David Jenkins]

For the headsets I'm using some Terratrip ones:




I've got a windscreen so helmets aren't needed....

I don't think there's any real way round the slight switch on time for VOX but you get used to in the end.
I'm going to have a PTT and "permanent on" button on the box anyway for people who don't like the VOX function.

I bought a cheap motorbike intercom set from Aldi or similar for a fiver. Seems to work ok, CBA to make one.

Now the only thing I've got to try and work out is how to keep the thing simple yet allow all the various combinations of VOX and muting for a mp3 player, an intercom, a PMR radio, a mobile phone (or two) and possibly a GPS unit.... And I'm also fitting a simple beeper from the indicators to remind me when they're flashing (I won't be able to hear the ticking)....

It also gets complicated in that the passenger may or may not want to listen to the PMR or mobile (probably won't want the indicator alarm!) but may still want to use the intercom etc....

Gets complicated and I'm trying to avoid resorting to a PIC for the logic table so that other people (without PIC writing capabilities) will be able to make one... Then again, a PIC programmer is cheap as chips.... We'll see!!!!