Multi-line telephone intercom

Modern smartphones have become so ubiquitous these days that old analog phones are being left behind. However, you may still have a few of these old phones lying around your house collecting cobwebs or you may have seen them lying around on the shelves of your local thrift store. Now is your chance to put it to good use. In this video, Derek takes you back to a time when stretching a telephone cord across the room was the norm by creating a 4-line telephone intercom system with basic ringing capability. The circuit surrounds a DTMF decoder IC that handles key detection, a simple AC inverter to handle the ringing, and a current source that allows analog communication between multiple phones: http://bit.ly/2Leyf7C

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