Telphone convenient lamp circuit

Published:2011/7/9 2:31:00 Author:Fiona | Keyword: convenient lamp | From:SeekIC

Telephone convenient lamp circuit is shown as above,S is the tact switch connected with microphone key,it is off at ordinary times, it is connected in off-hook status.HA is piezoelectric ceramic chip which is pasted in the speaker YD,L1 and L2 are the telephone lines.When it has no ringing signal or it isn't in off-hook state,3 terminal of NE555 is low potential,relay J does not work,and when it has a ringing signal or it is in off-hook state, J is conducted to make K close and H light.it is thus clear that the convenient lamp provides timely lighting when you receive and make a call at night.



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