As shown in the figure is a multi-function timing call circuit. The circuit is composed of a buck rectifier circuit, a monostable delay circuit, a music integrated circuit, a relay control circuit, a speaker, etc. The step-down rectifier circuit provides DC voltage for the entire circuit. In this circuit, the switches K2 and K3 are placed in different positions to realize different functions.
Put K3 in the "doorbell" position. Press the button AN to make the music integrated circuit emit a music signal and drive the speaker to emit music sound. Realize the "doorbell" function.
Put K3 in the "Call" position and K2 in the "Announcement" position. After dawn, the photoresistor RG is exposed to low resistance due to light, so that BG1 is cut off, C. 1 Charge through R1 and W1. When the charge reaches â‘¥ pin potential reaches 2 / 3VDD, 555 resets. â‘¢ The low level output by pin causes J1 to pull in and J2 to release. At the same time, it triggers the sound circuit to work and emits a warning sound Realize the "Report" function. The time interval from dawn to report can be changed by adjusting W1, that is, by changing the time constant of the charging circuit to achieve "delay report".
Put K3 in the "call" and K2 in the "timing" position, then BG1 ends. After powering on, C1 is charged through W1 and R4, and its charging time td = 1.1 (Rw1 R4) C1, that is, the timing time, the illustrated parameter corresponds to about 150 minutes. When the time is up, pin 555 turns to low level to make J1 pull in and J2 release, cut off the power of the device, so as to realize the function of "timed on and off".
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