Here's what you need:
- 2 analog telephones
- 1 100-foot phone cord
- 1 9-volt battery
- 1 300 Ohm resistor
The intercom system connection consists of two copper wires. Typically, the wires are colored red and green. The green wire is common, while the red wire supplies your phone with 6 to 12 DC volts at about 30 miliamps.
The easiest way to wire a private intercom is to start with the 100-foot phone cord. Cut it, strip the wires, and hook in the battery and resistor (as shown below). When two people pick up their phone receiver, they can talk to each other! This configuration will work at distanced of up to several miles apart.
However, there is one thing this little intercom system can't do: It cannot ring the phone to tell the person at the other end that they have a call. The "ring" signal in the US is a 90-volt AV wave at 20Hz; Europe's is a 60 - 90-volt AC at 25Hz.
|Photo Source: Clear-Com Intercom Expert|