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DIY Intercom System

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nuckollsr(at)cox.net
Guest

Posted: Fri Apr 13, 2007 5:24 am Post subject: DIY Intercom System

At 09:30 AM 4/12/2007 -0700, you wrote:



 	  Quote: 	
		  



Hello Listmembers,



I would like to introduce myself. I'm a brand new builder of a Zenith 

Zodiac XL kit. I plan to do a lot of electronics mods myself (flunked 

polytechnic college in a previous life many moons ago).



I have Bob's book and I think it's great. has anybody on the list ever 

attempted to build a two place intercom? I think the intercoms on the 

market are way overpriced. I found schematics for a David Clark intercom 

on their website and think about using that for inspiration.


	


   The audio portion of an intercom is stone simple. The

   tricky part is development of a background noise reduction

   system that's effective, drift free and relatively immune

   to variables in ambient noise.



   Designs of yore used a simple rectifier of total signal

   and a comparator to decide when signal levels were high

   enough (because someone's voice was added to background

   noise) to open the signal gate and allow everything (voice +

   noise) to be heard in everyone's headphones.



   There's a wealth of signal+noise to noise deduction philosophies

   with the more modern techniques using rudimentary digital

   signal processing software in a microcontroller to do

   the threshold adjustments and make gating decisions in

   real time. These intercoms don't have or need "squelch"

   adjustment knobs.



   The systems that do have manual adjustments can benefit

   from a variety of active filter techniques that improves

   the squelch system's ability to sort speech signals from

   noise signals. What you pay for in an commercial-off-the-shelf

   (COTS) intercom system is a whippy noise gating system and usually

   with a warranty. If you don't like it, you can generally

   get you money back with a minimum investment of $time$.



   It's not my intent to discourage you from attempting

   a satisfactory design on your own but be advised that

   when all the solder joints have cooled and you have

   a successful system running in your airplane, you will

   have invested much more $time$ on the project than you would

   have expended on a COTS product.



   I've got some ideas for a software based noise gating

   system I'd like to try and I've discussed it with my

   software guru but this project is WAY back on the

   burners. The development effort is significant and

   the competition in this arena is competent and

   in my never humble opinion, nicely priced. I'm doubtful

   that it's worth my $time$ to step into that bull-fight.



   Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

klehman(at)albedo.net
Guest

Posted: Fri Apr 13, 2007 7:23 am Post subject: DIY Intercom System

Sorry I can't find your name but for the original person asking, while 

any homemade intercom is likely better than no intercom you might also 

be content with the intercom that is included as part of some  VHF 

radios such as the Iccom A200 although I don't think that particular one 

has Voice activation.



Bob I agree that it is probably not good use of time for most folks to 

try and improve on something like the Flighttech hot mic intercom that 

has no background noise that I can notice, whether someone is talking or 

not.  I think it uses a chip developed for telephone use rather than 

custom DSP technology but it works amazingly well for me and the price 

is right.



I guess I've only used the cheaper VOX intercoms but even with matched 

headsets and perfectly adjusted squelch, they seem to pick up a lot of 

background noise when someone is talking.  Maybe the high end units are 

better but I'd never go back to a VOX unit.



Ken



Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



 At 09:30 AM 4/12/2007 -0700, you wrote:



> 

>

> Hello Listmembers,

>

> I would like to introduce myself. I'm a brand new builder of a Zenith 

> Zodiac XL kit. I plan to do a lot of electronics mods myself (flunked 

> polytechnic college in a previous life many moons ago).

>

> I have Bob's book and I think it's great. has anybody on the list 

> ever attempted to build a two place intercom? I think the intercoms 

> on the market are way overpriced. I found schematics for a David 

> Clark intercom on their website and think about using that for 

> inspiration.

   The audio portion of an intercom is stone simple. The

   tricky part is development of a background noise reduction

   system that's effective, drift free and relatively immune

   to variables in ambient noise.



   Designs of yore used a simple rectifier of total signal

   and a comparator to decide when signal levels were high

   enough (because someone's voice was added to background

   noise) to open the signal gate and allow everything (voice +

   noise) to be heard in everyone's headphones.



   There's a wealth of signal+noise to noise deduction philosophies

   with the more modern techniques using rudimentary digital

   signal processing software in a microcontroller to do

   the threshold adjustments and make gating decisions in

   real time. These intercoms don't have or need "squelch"

   adjustment knobs.



   The systems that do have manual adjustments can benefit

   from a variety of active filter techniques that improves

   the squelch system's ability to sort speech signals from

   noise signals. What you pay for in an commercial-off-the-shelf

   (COTS) intercom system is a whippy noise gating system and usually

   with a warranty. If you don't like it, you can generally

   get you money back with a minimum investment of $time$.



   It's not my intent to discourage you from attempting

   a satisfactory design on your own but be advised that

   when all the solder joints have cooled and you have

   a successful system running in your airplane, you will

   have invested much more $time$ on the project than you would

   have expended on a COTS product.



   I've got some ideas for a software based noise gating

   system I'd like to try and I've discussed it with my

   software guru but this project is WAY back on the

   burners. The development effort is significant and

   the competition in this arena is competent and

   in my never humble opinion, nicely priced. I'm doubtful

   that it's worth my $time$ to step into that bull-fight.



   Bob . . .

echristley(at)nc.rr.com
Guest

Posted: Fri Apr 13, 2007 8:44 am Post subject: DIY Intercom System

Robert L. Nuckolls, III wrote:



 	  Quote: 	
		  

   It's not my intent to discourage you from attempting

   a satisfactory design on your own but be advised that

   when all the solder joints have cooled and you have

   a successful system running in your airplane, you will

   have invested much more $time$ on the project than you would

   have expended on a COTS product.


	




Just as a single data point....



I built the RST panel mount kit.  The parts all went together quickly 

and easily with the connectors being the hardest part.  I believe the 

total cost was right at $130.  I had about 20 hours total invested in 

building it.



The pay back for me is being able to lay my hand on it and say, "EYE 

built that," with my chest pushed out.  Unless you're as egotistical as 

I am, it may not pay you to go this route.  OTOH, I'm actually saddened 

that RST is no longer selling their DIY radio kits.



-- 

         ,|"|"|,              Ernest Christley       |

----===<{{(oQo)}}>===----    Dyke Delta Builder      |

        o|  d  |o        http://ernest.isa-geek.org  |

hansriet

Joined: 09 Feb 2007
Posts: 93

Posted: Sun Apr 15, 2007 3:19 pm Post subject: Re: DIY Intercom System

Thanks for all the advise.

I decided to use my time to build the plane and bought an used intercom on eBay.



Hans

trigo(at)mail.telepac.pt
Guest

Posted: Sun Apr 15, 2007 5:10 pm Post subject: DIY Intercom System

Smart decision.



Carlos

---

az_gila

Joined: 17 Jun 2006
Posts: 99
Location: Tucson, AZ

Posted: Fri Apr 20, 2007 9:33 pm Post subject: Re: DIY Intercom System

I'd like to see a easy (cheap) audio mixer for use with a commercial intercom.

Simple panels probably only have 3 or 4 audio sources (including alerts) and a full audio panel is way overkill.  Most folks don't even use the speaker any more, so phones only are OK.



I was thinking of a simple audio mixer and a Tx1/Tx2 switch.. perhaps from a ready made kit... such as this one...



http://store.qkits.com/moreinfo.cfm/FK652



Would like to hear other suggestions....



gil in Tucson



PS  I got a working PM1000 intercom for $50 on e-bay, so the intercom bit is taken care of...

nuckollsr(at)cox.net
Guest

Posted: Tue Apr 24, 2007 4:25 pm Post subject: DIY Intercom System

At 10:33 PM 4/20/2007 -0700, you wrote:



 	  Quote: 	
		  



I'd like to see a easy (cheap) audio mixer for use with a commercial intercom.

Simple panels probably only have 3 or 4 audio sources (including alerts) 

and a full audio panel is way overkill.  Most folks don't even use the 

speaker any more, so phones only are OK.



I was thinking of a simple audio mixer and a Tx1/Tx2 switch.. perhaps from 

a ready made kit... such as this one...



http://store.qkits.com/moreinfo.cfm/FK652



Would like to hear other suggestions....


	




  See:



http://www.aeroelectric.com/DIY/Audio_Isolation_Amplifier.pdf

    Bob  . . .

az_gila

Joined: 17 Jun 2006
Posts: 99
Location: Tucson, AZ

Posted: Tue Apr 24, 2007 8:30 pm Post subject: Re: DIY Intercom System

Bob... if I wanted to switch sources on and off, would a switched short to ground between the input resistor and capacitor for a single input work?



Such as shorting the junction of R104 and C112 to ground (page 1.8.1 schematic) 



gil A

nuckollsr(at)cox.net
Guest

Posted: Wed Apr 25, 2007 5:09 am Post subject: DIY Intercom System

At 09:30 PM 4/24/2007 -0700, you wrote:



 	  Quote: 	
		  



Bob... if I wanted to switch sources on and off, would a switched short to 

ground between the input resistor and capacitor for a single input work?



Such as shorting the junction of R104 and C112 to ground (page 1.8.1 

schematic)



gil A


	


   Yes.



   Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

az_gila

Joined: 17 Jun 2006
Posts: 99
Location: Tucson, AZ

Posted: Wed Apr 25, 2007 6:28 am Post subject: Re: DIY Intercom System

Thanks Bob...



I presume a short (less than 6 inches) twisted pair to a panel switch would do the job...



gil A

nuckollsr(at)cox.net
Guest

Posted: Wed Apr 25, 2007 4:25 pm Post subject: DIY Intercom System

At 07:28 AM 4/25/2007 -0700, you wrote:



 	  Quote: 	
		  



Thanks Bob...



I presume a short (less than 6 inches) twisted pair to a panel switch 

would do the job...



gil A


	


    Sure.



   Bob . . .

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