555 time control password electronic doorbell circuit

  
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As the figure 15-22 shows, the doorbell is composed of the monostable timing circuit, the password switch, the NAND gate circuit and the sound circuit.etc. In the limited time, the circuit uses the program to press the password switch, the doorbell circuit sends out the alarm sound. If it exceeds the specified time or the password is wrong, there is no sound..
555 time control password electronic doorbell circuit - schematic




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