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Sanhe Brand Anti-Theft Door Talkback Doorbell Analysis Circu

2014-11-02 03:12  
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Sanhe Brand Anti-Theft Door Talkback Doorbell Analysis Circuit
The corridor anti-theft door is the public protection facilities of the urban families. Its talkback doorbell would offen have faults in house decoration and normal using. This article introduces the Sanhe brand SH25 type anti-theft door talkback doorbell (indoor device) working principle which would be reference for maintaining this device and other equivalent products. The circuit is shown in the picture (in the picture the voltage marked with CN1 is the practically tested voltage when open circuit).1.Visitors pressing the button to call the master. When the visitors press the corresponding room number's doorbell switch, the CN1's pin 3 would send DC voltage to supply the working voltage for the IC1 through R11 for voltage divider. And the voltage would be bucked through R5 that indicates the working mode by Z3. Also it is changed to be 3V voltage as the working power of the musical chip IC2 (KD-9300A) through R8's voltage step-down and Z1's voltage regulator. At the same time the C8 would complete the triggering. The IC2 would generate the doorbell's calling signal and then send to the tone amplifier IC1 (LM386) for amplification. And then it would output from the pin 5 and is send to the headphone for sounding through the key switch, C4, RW2. Thus it completes the doorbell calling.