555 alarm, doorbell and lighting controller circuit

Published:2011/5/30 10:11:00 Author:TaoXi | Keyword: 555, alarm, doorbell, lighting, controller | From:SeekIC

As the figure 15-24 shows, the controller circuit is composed of the switch type Hall integrated circuit DN838 and the astable multivibrator (composed of the 555), this circuit can be used in wide range of applications such as the automatic door opening, automatic delay alarm, automatically turns off the lights and also it can be used as the doorbell. The astable multivibrator is composed of the IC(555) and R1，R2，C1, the oscillation frequency f=1.44/(R1+2R2)C1, it is about 1000Hz. The reset switch and the SCR trigger switch are composed of the DN838 and the small magnets. When the DN838 loses the magnetism, poins A and B conduct, SCR is trigger conduction, the light turns on, the 555 starts working, the piezoelectric ceramic HTD sends out the alarm. When you close the door, the DN838 receives the magnetism, points A and B cut off, the SCR cuts off too, the light turns off.



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