Multichannel Telephone based intercom

sumdawgy

I setup a simple intercom using 2 home phones & 9vdc wart.

But, I need to setup at minimum..a second "line/channel" That I plan to connect a to a "small" amplified speaker system (probably with an old speaker phone for simplicity).. allowing the phones to be used a PA system.

But, instead of multiple power supplies... I'd like to feed the lines from one source....

I can't seem to find anything online to guide me..

Best I can think of is...... using 10 Ohm resistors to feed each channel W/ filter caps (and possibly choke coils) on supply sides to prevent cross channel talking.

Can anyone point me in the right direction?

kwinn

Not sure what you want. Can you provide a diagram?

sumdawgy

(The image is actually attached now.
Sorry, Vista tried to install svc pk2 but failed and left me holding the bag for a few days....)

Using a couple of old standard phones.....

Dedicating one phone to be off-hook it's output amplied to speakers. (paging)

Each station can select from 3 channels. (Rotary selector?)
[In future using prop/bs2 (hub) & 8 bit shift registers (stations)]

I'm thinking....
c3-c5 should be small disc caps. (and perhaps between L1 & R1 (respectively))
L1--Not sure of value
R1--10Ohm wire wound 1Watt.

I realize I"m rebuilding a wheel...
But I can't seem to find this wheel's layout anywhere....

kwinn

An inductor to block audio would need to be fairly large, and I think are not needed. I would put a diode between the main supply and each leg going to the phones and PA. That along with the capacitors and resistors should be enough.

sumdawgy

Makes sense. I was so concerned with A/C sig, I wasn't thinking of Diode for that...
Should work fine as long as I don't allow the current draw to create an A/C signal from the draw through the diodes....

And yeah, simpler/smaller than the L/C circuit I was envisioning...
I'll have some time to breadboard a test circuit this weekend...

Thanks for the direction change!