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8 Line intercom using 89c51

8 Line intercom using 89c51

This project is aimed to make the low cost intercom system which 8 lines may interact with this hardware.

Main Board:
In this card there is 89c51 microcontroller is used. Micro controller is the controller the MT8870 and MT8816 DTMF encoder analogue switch.

SLIC card:
In this card there is a constant current source is used to activate the phone. The LM339 is used to detect out of hand and the hand of the condition. There are circuits repeat the same because we have the phone interface 8.

When the phone on hand in the output of the LM339 change is detected by the microcontroller that the phone is in the area, then make the microcontroller is using the MT8816 analog channel. the LM555 is used to generate a dial tone.