MT8870 DTMF Decoder Protection Circuit

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kygh_qin

Joined Nov 29, 2009
6
i m currently working on a caller id project using PIC18F4455. MT8870 is used in this project. however, Fixed telephone line cannot be connected to MT8870 directly. i had found two types of protection circuit from the internet. but i dont know which one is better and dont know how they works actually.
 

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