Intercom with 6 wired phones

Thread Starter

TiagoPais

Joined Jun 20, 2017
3
Hello
I know how to make a simple intercom with 2 wired phones.
But i want to make a intercom with 6 wired phones. I just need to make all the 6 wired phones talk and year together. I don't need ring tone and other extra things. I just need to can put all the 6 person to talk and list together in simultaneous system.
Thank for your help.
 

Externet

Joined Nov 29, 2005
2,202
Nice. Would be good to know if less than six telephones will be used at certain times.

I would try a series scheme:

36V(+)----------phone1---------phone2-------- . . . . --------phone6------------(-)

Each telephone should have a 200 Ohm 0.5Watt resistor connected to its seize switch, so when 'off hook', the resistor path is out of circuit and the current path is the telephone. The seize switch should put the resistor in the current path when 'on hook' and not into the telephone circuitry path.

It could also work with all the telephones permanently in series with their seize switches forced 'off hook'; Turning the 36V supply on when wanted to operate them.
 

crutschow

Joined Mar 14, 2008
34,285
Here's a discussion on using multiple phones as an intercom

A quote from that:

"A simple way could be this. You need a DC power supply that can supply > 40Vdc and is current limited to about 40mA and has an output impedance that allows voice signals to develop on the line. You could use a 1kohm resistor for doing this but watch the power rating - probably need a 2W resistor from quick brain math.

All the phones are connected in parallel and there's a good chance that when you pick one phone up and tap the hookswitch it'll cause ring sounds to emit from the other phones. It may not be great but it's easy to try. If some phones don't produce a sound then maybe try a higher supply voltage and higher resistance. If this doesn't work then scrap the idea!!!!

When it comes to speaking, there may be a little sidetone issue in that you will hear your own voice in the earpiece a little louder than when using a normal phone. This is because phones tend to prefer 600 ohms and connecting two together is fine providing the pair are current fed (or via a big inductor) but this uses a further 1k ohms in the supply and more sidetone will be present - a minor issue.
"

So basically you connect a 1kΩ, 2W resistors in series with a 40V-48Vdc power supply and connect all the phones in parallel with that.
Edit: It might work okay with a lower voltage and resistor, such as 24Vdc with a 600Ω, 1W resistor, if that's more convenient.

You could use the phone lines in you house for connection if they are not being used for a landline service.
You could also likely use the unused pair of wires in the house phone wiring for the intercom.
 
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