Trying to make a multiple station intercom

[jbrols]

Hi!

There probably have been some similar discussions, but still...

I would like to build a 4 or 5 station in-house intercom. I've searched for a "not too complex and yet promising" circuit, but nothing really miraculous popped out.
So far only two designs seem to match my criteria:

1. The one from here. A good thing would be the absence of microphones, so no parasitic feedbacks or ringing could occur (maybe); it uses just one power supply; it uses just three wires for each station. But it "talks" to all stations simultaneously, which is not desirable.
2. The one from here (the middle of the page). A good thing is the common power supply and the fact, that the stations are independent. But it uses many wires for each station (number of stations + two), and it may be problematic to get rid of microphone ringing at some specific situations.

I have made the two test stations of the second intercom, and it seems to work, but the output transistors get hot randomly (especially the BC547), even when inactive. Sometimes they don't. Could you, please, take a look at the schematic for possible improvements?

I'm still open to any other suggestions of some better designs, if you would be willing to share them.

Thank you.

Edit: Just now saw, that this is my first post here 😱.

 

[franzm]

What about a carrier frequency system?

 

[jbrols]

What about a carrier frequency system?

Sorry, I should have mentioned, that I'm not extremely clever in electronics 😀. So your sentence is a bit of a mystery to me...

 

[franzm]

Just search for carrier current intercom:
Carrier signal - Wikipedia, the free encyclopedia
Frequency-division multiplexing - Wikipedia, the free encyclopedia
Wireless Intercoms & Baby Monitors
http://www.elect.mrt.ac.lk/ug_papers/pr10_2003.pdf
Carrier current - Wikipedia, the free encyclopedia
Intercom telephone
http://www.ti.com/lit/an/snaa087/snaa087.pdf
Carrier-current intercom | Electronics Forums

 

[jbrols]

Thanks, franzm, for such a detailed explanation of the term regarding the intercom.
I knew, what the carrier frequency as such was, but I just never thought about it in connection to intercoms (my narrow thinking 😱).
Still, it would be fair to say, that I have not grown to this level of electronics yet, so my best bet would be to stick to some of the more simple solutions. Like the one I already tested, if only the output transistors wouldn't heat so irregularly. Maybe there are some mistakes in the schematics? Or should I just put some stronger transistors in there?

 

[jbrols]

Please, help me with this intercom setup.

Hello again!

There just had to be some problem in all this, because it worked so well at the testing stage !
So, after a successful two-station testing, I made all four of them and connected together as seen in Intercom_.gif. But all I got was nothing, except some clicking sound, when pressing corresponding buttons.

Can you, please, take a look at all this and try to find a cause for this problem? I really would like to make it work as it should.

Thank you.

 

[jbrols]

Never mind...