Telephone automatic recording control circuit

Published:2011/7/15 3:15:00 Author:Fiona | Keyword: automatic recording control | From:SeekIC

Voltage comparator which is compose of integrated circuit IC1 ( LM741) and external components is used for monitoring the telephone line voltage between L1 and L2. When the ordinary dial-up telephone is in hook state,the voltage between L1 and L2 is about 60V;when having a ringing current,it adds communication signal about 100V;when picking up the telephone receiver,the voltage between L1 and L2 drops to about 10V. Using this voltage change can judge out the telephone working state.Every time when picking up the telephone receiver,the control circuit automatically charges the recorder,then the recorder begins recording;when hanging up the telephone,the recorder automatically turns off the power to stop the recording.



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