As shown in the figure is a multi-function timed call circuit. The circuit is composed of a buck rectifier circuit, a monostable delay circuit, a music integrated circuit, a relay control circuit, and a speaker. The buck rectifier circuit provides a DC voltage to the entire circuit. This circuit can achieve different functions by placing switches K2 and K3 in different positions.
Place K3 in the "doorbell" position. Pressing the button AN causes the music integrated circuit to release one music signal and drive the speaker to emit the music. Implement the "doorbell" function.
Put K3 in the "Call" position and K2 in the "Call" position. After dawn, the photoresistor RG is low-impedance by the light, so that BG1 is cut off, C. 1 After R1 and W1 are charged, when the charge reaches the potential of 6 feet to reach 2/3VDD, 555 is reset, the low level of the 3 pin output makes J1 pull in, J2 is released, and the sound circuit is triggered to work, and the sound is heard. Achieve the "report" function. The time interval from dawn to announcement can be changed by adjusting W1, that is, by changing the time constant of the charging circuit to achieve "delay announcement".
Put K3 in "Call" and K2 in "Timed" position, then BG1 is cut off. When turned on, C1 is charged by W1 and R4, and its charging time td=1.1 (Rw1 R4) C1, that is, the timing time, the corresponding parameter corresponds to about 150 minutes. When the timing is up, 555 3 feet turn to low level, so that J1 pulls in, J2 releases, cuts off the power of the device, thus realizing the function of “timed on and offâ€.
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