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Call finder circuit

2014-11-22 18:20  
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Call finder circuit
The work principle of the circuit: in the circuit, J1 is connected to the telephone line. When there is no call in, Vcc is 0V for there is no ringing signal. The circuit does not work with no power source voltage. When there is call in, the ringing signal is current limited by the R1, through C1, C6 coupling, bridge VD1 rectifier, C4 filter to supply power voltage Vcc for the whole device. By detecting, Vcc changes from 1.8V to 4.2V with ringing signal, but it does not affect the function.