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Intercom question

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jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Tue Feb 03, 2015 11:27 am Post subject: Intercom question

My EAA chapter has spawned a group of young people known as the "Young Aviators". They are constructing a mockup of a B-25 that they are planning to transport to Oshkosh this year. A question has come up... is there a simple way to hook up 7 individual headsets w/ microphones so that the entire "crew" can talk back & forth, without having to somehow patch together off the shelf  4 or 2 place intercoms? Some kind of simple circuitry that could be easily built? Thanks in advance for any ideas or suggestions.



John Evens

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John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

nuckolls.bob(at)aeroelect
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Posted: Wed Feb 04, 2015 12:36 pm Post subject: Intercom question

At 13:27 2015-02-03, you wrote:

 	  Quote: 	
		  



My EAA chapter has spawned a group of young people known as the 

"Young Aviators". They are constructing a mockup of a B-25 that they 

are planning to transport to Oshkosh this year. A question has come 

up... is there a simple way to hook up 7 individual headsets w/ 

microphones so that the entire "crew" can talk back & forth, without 

having to somehow patch together off the shelf  4 or 2 place 

intercoms? Some kind of simple circuitry that could be easily built? 

Thanks in advance for any ideas or suggestions.


	


   What kind of microphones/headsets? Aviation

   style? Over what distances are the wires

   routed?  The task is 'easy' . . . just

   need some details on the hardware you

   plan to use.



   Bob . . .

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jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Fri Feb 06, 2015 9:14 pm Post subject: Re: Intercom question

Thanks, Bob. It looks like they are going to use aviation headsets... probably donated units of various brands. Not everyone has to necessarily be able to "transmit" (push-to-talk) to the other headsets - perhaps only 1 or 2 ("pilot" & "co-pilot"), & everyone else able to hear at least. The mock-up is basically of the nose section, so maximum distances of wire runs would be approximately 10 or 15 feet. The leaders of this project feel that it will add to the experience if the kids can connect in this way. BTW, this project is written about in the latest "Sport Aviation" magazine on p.110.

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John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

dbrown2(at)nycap.rr.com
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Posted: Sat Feb 07, 2015 4:13 am Post subject: Intercom question

Just read the article ...very cool!



--

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nuckolls.bob(at)aeroelect
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Posted: Sat Feb 07, 2015 6:41 am Post subject: Intercom question

At 23:14 2015-02-06, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jrevens" <jrevens(at)comcast.net>



 Thanks, Bob. It looks like they are going to use aviation headsets... probably donated units of various brands. Not everyone has to necessarily be able to "transmit" (push-to-talk) to the other headsets - perhaps only 1 or 2 ("pilot" & "co-pilot"), & everyone else able to hear at least. The mock-up is basically of the nose section, so maximum distances of wire runs would be approximately 10 or 15 feet. The leaders of this project feel that it will add to the experience if the kids can connect in this way. BTW, this project is written about in the latest "Sport Aviation" magazine on p.110.



 --------

 John Evens 	




   Understand. My recommendation is to start with

   any sort of pre-packaged audio amplifier. One

   like this would work nicely.



 [img]cid:.0[/img]



  There are dozens of similar devices on eBay. I've

  used a bunch in various applications with good

  results and value. You can power them up with a

  12v 'wall wart'. In fact, if you'll shoot me an

  address, I donate an amplifier and power supply

  to the project.



  The next thing you need to do is cobble up the

  interface that makes an aircraft microphone 'look'

  like something found in the rest of the world . . .



 [img]cid:.1[/img]



   A circuit like that shown above will allow

   you to bias-up and mix as many microphones

   together as needed. PTT  for any particular

   mic can be a simple n.c. push button in parallel

   with the microphone. The button shorts out the

   mic unless being used. This is preferable to

   putting a n.o. button in series . . . the

   parallel configuration reduces the DC level

   shift and resulting 'pop' you hear in the system

   as any one microphone is keyed.  



   Headphones can simply be paralleled assuming

   they're all about the same efficiency where volume

   can be managed by the single control on the amplifier.

   Recommended circuitry not shown is a 220 ohm, 1/2

   watt resistor in series with each line out to

   a headset. At worst, you may have to balance

   relative audio levels in the headsets which

   can be accomplished by adjusting the value of that

   220 ohm resistor.



   Got somebody in your group that's handy

   slinging solder?



 



 

   Bob . . .

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jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Sun Feb 08, 2015 11:55 am Post subject: Re: Intercom question

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 23:14 2015-02-06, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jrevens" <jrevens>



 Thanks, Bob. It looks like they are going to use aviation headsets... probably donated units of various brands. Not everyone has to necessarily be able to "transmit" (push-to-talk) to the other headsets - perhaps only 1 or 2 ("pilot" & "co-pilot"), & everyone else able to hear at least. The mock-up is basically of the nose section, so maximum distances of wire runs would be approximately 10 or 15 feet. The leaders of this project feel that it will add to the experience if the kids can connect in this way. BTW, this project is written about in the latest "Sport Aviation" magazine on p.110.



 --------

 John Evens 	




   Understand. My recommendation is to start with

   any sort of pre-packaged audio amplifier. One

   like this would work nicely.



 [img]cid:.0[/img]



  There are dozens of similar devices on eBay. I've

  used a bunch in various applications with good

  results and value. You can power them up with a

  12v 'wall wart'. In fact, if you'll shoot me an

  address, I donate an amplifier and power supply

  to the project.



  The next thing you need to do is cobble up the

  interface that makes an aircraft microphone 'look'

  like something found in the rest of the world . . .



 [img]cid:.1[/img]



   A circuit like that shown above will allow

   you to bias-up and mix as many microphones

   together as needed. PTT  for any particular

   mic can be a simple n.c. push button in parallel

   with the microphone. The button shorts out the

   mic unless being used. This is preferable to

   putting a n.o. button in series . . . the

   parallel configuration reduces the DC level

   shift and resulting 'pop' you hear in the system

   as any one microphone is keyed.  



   Headphones can simply be paralleled assuming

   they're all about the same efficiency where volume

   can be managed by the single control on the amplifier.

   Recommended circuitry not shown is a 220 ohm, 1/2

   watt resistor in series with each line out to

   a headset. At worst, you may have to balance

   relative audio levels in the headsets which

   can be accomplished by adjusting the value of that

   220 ohm resistor.



   Got somebody in your group that's handy

   slinging solder?



 



 

   Bob . . . 	




Thank you so much, Bob! That's exactly what I was hoping for.

I'm sure I can handle building the mic mixing circuit. If I used an

adjustable 1/2 watt potentiometer to each headset, what value 

would you recommend - 220 ohm, or higher? Probably a stupid 

question, but what type capacitors should I use - electrolytic, or?

I would gratefully accept your offer of an amp & power supply... 

I will send you an email. Again, from myself, our chapter, and 

the Young Aviators - thank you!!

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_________________
John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Feb 08, 2015 2:09 pm Post subject: Intercom question

 	  Quote: 	
		  Thank you so much, Bob! That's exactly what I was hoping for.

I'm sure I can handle building the mic mixing circuit. If I used an

adjustable 1/2 watt potentiometer to each headset, what value

would you recommend - 220 ohm, or higher? Probably a stupid

question, but what type capacitors should I use - electrolytic, or?

I would gratefully accept your offer of an amp & power supply...

I will send you an email. Again, from myself, our chapter, and

the Young Aviators - thank you!!


	


   Got the mailing address. I dug out an amplifier

   and power supply. Need to find my MP3 player to

   test it for functionality.



   What you might consider is a volume control

   at each station where a headset is plugged in.

   Set the master volume on the amplifier on

   the 'generous' side and let each station

   set their own volume to suit.



   There's some other options to consider. If

   some of the stations are listen-only, you

   could use contemporary headsets (10-50

   ohm) for a lot less money than aviation

   headsets (100+ ohms).  Each station's

   volume control would be a 50-ohm,

   wire wound potentiometer.



http://tinyurl.com/nqruvxd



   The capacitors shown are all electrolytic.

   Any time you see a "+" sign associated with

   the symbol, that tells you that it's some

   form of electrolytic. I've got all those

   parts in my sand-box-bins. I'll include

   a kit of loose parts with the amplifier.



   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Fri Mar 13, 2015 3:02 am Post subject: Re: Intercom question

Here is a link to the B-25 Project for KidVenture:

http://tinyurl.com/B-25-Project

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