555 doorbell, talkback, alarm three functions circuit

Published:2011/6/2 1:01:00 Author:TaoXi | Keyword: 555, doorbell, talkback, alarm, three functions | From:SeekIC

The figure 15-26 shows the switch position of the doorbell talkback functional status. AN1 is the doorbell button switch, when someone presses the AN1, the main circuit gets the power, and the two audio oscillators which is composed of the F3，F2，R4，R5，C3 and F4，F5，R7，R8，C4 start working, and it is compounded in RP1, then it adds to the VT1 to be amplified to drive the speaker. If the master opens the four-blade double-throw switch K1, the circuit is in the talkback state. If you press AN2, the voice of master will be received by the indoor speaker, then it is amplified to drive the outdoor speaker. The main circuit which is composed of the IC1(555) and R1，R2，C1 produces the 0.5Hz low frequency oscillation.



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