Apartment Intercom Stations

[ILIASB000]

I am new to this Forum. This is my 1st Question. I have a Question about Old style Apartment Building Intercom Systems(e.g. Nutone 478, Tektone, Etc.) The Intercom Station in each Apartment usually has 3 Buttons; "Listen", "Talk". and "Door". I basically have 2 Questions;
(1) What happens if both "Listen", and "Talk" Buttons are Pressed at the same time. Which Function will override the other "Listen Function", or, "Talk Function"? This can also happen if in 1 Apartment someone pushes the "Listen" Button, while in some other Apartment someone pushes the "Talk" Button. Will 1 Button Override the other, or, neither will work?
(2) Can Pushing both "Listen" and "TalK" Button damage the Intercom System, or, there is Protection Circuits in the Intercom for this Scenario?

Thanks

 

[betwixt]

These things are entirely up to the designer of the intercom, there is no standard. I doubt anyone would hold the listen button down all the time, they would only use it if someone had already pressed the door button to alert them that someone was trying to talk. If they did hold it down all the time they would probably hear the audio from all the intercoms that had talk pressed at the same time.

Clever systems that allow multiple sessions simultaneously are possible to avoid the problem but are obviously more complicated and expensive.

Brian.

 

[BradtheRad]

There are methods at the hands of a knowledgeable designer.
Off the top of my head I think of introducing a DC voltage as a 'keep alive' signal activating a particular intercom for 30 seconds after a visitor pressed that button in the lobby.

Any successful manufacturer needs to have one star performer in electronics, who can arrange components available in that day (diodes, capacitors, transistors, resistors). In this case, to create circuitry that admits communication to your intercom, yet blocks that signal prevent someone else from listening in on your communication.

 

[betwixt]

I would guess that the simplest method is just to have a "busy" signal that activates if any button is pressed anywhere and blocks all further actions until it is deactivated. That method only needs one wire to connect it all intercoms.

Brian.