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2 Line Intercom with Telephone Line Changeover Circuit:   circuit presented here can be used for connecting two telephones in parallel and also as a2-line intercom. (added 3/03)

Creating Your Own Telephone Ne2 Rk:  you can easily create your own intercom system using two telephones, a 9-volt battery (or some other simple power supply) and a300-ohm resistor (added 4/02)

Door Phone Intercom:  (schematic / circuit design added 9/02)

Full-Duplex Intercom:  No complex switching required Simple circuitry, 6-12V supply  (added 3/05)

Head Set Intercom :  (diagram added 6/03)

High Quality Intercom:  (electronic design added 10/06)

High Quality Intercom:  (schematic / circuit design added 9/02)

IFB Intercom :  (diagram added 6/03)

Intercom Preamp:  a convenient way of making an intercom is to use a loudspeaker as a microph1(added 4/02)

Intercom Schematic:  (electronic circuit added 4/05)

Low Cost Intercom using Transistors:  The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 and T2 gets converted into an asymmetrical astable multivib-rator generating ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece.  Current consumption.... (added 10/05)

Low Cost Transistorised Intercom:  (electronic Circuit / Schematic added 10/04)

Low Power Op Amp   Audio Amp (Intercom):  (circuit / schematic design added 6/06)

Old phones as an intercom (circuitsdb):  From: mwandel@bnr.ca (Markus Wandel) I have recently thought about this and come up with a kludgy but workable scheme. Talking over the phones is easy. You put DC current through the phone and.... (added 2/07)

Old Phones as an Intercom (ee.washington.edu):  (circuit added 7/02)

Old Telephones as Intercom:  (electronic Circuit diagram added 03/03)