555 time control password electronic doorbell circuit

Published:2011/6/7 5:16:00 Author:TaoXi | Keyword: 555, time control, password, electronic doorbell | From:SeekIC

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 signal. The timing switch circuit is composed of the IC1(555) and R1, C1, AN1, the timing time td=1.1R1C1, the figure parameter is 11 seconds. If you press AN1, the 555 will set, J and J1-1 contact point close to connect the power supply voltage of VT1～VT8，IC2，IC3.etc, the turn-on time is 11 seconds. The four groups of electronic switch is composed of the AN2～AN5，VT1～VT8.etc, the AN6～AN10 are the Invalid buttons.



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