How to build a simpler CMOS single zone alarm Explanation This is a simple single-zone anti-theft alarm circuit. Its functions include automatic entry and exit delays and timed Bell / alarm shutdown. It is designed for normal use with normally closed input devices, such as-reed contact-micro switch-aluminum foil tape-and PIRs. But it can be easily modified to accept normally open trigger devices-such as pressure pads. Welcome to reprint, this article comes from the electronic enthusiast network (http: //) It is easy to use. First check that the building is safe and the green LED is on. Then move to the "set" position of SW1. The red LED will light up. You have now left the building in about 30 seconds. When you return and open the door-the buzzer will sound. Then you have about 30 seconds to put SW1 to the "off" position. If you do not do this-the relay will energize and sound the alarm. The duration of the alarm will be the maximum length of the sound-not fixed. When the 15-minute cutoff timer starts running, only the normally closed loop has been restored. Although the loop is still open-the alarm will continue to be sound. If you want your alarm to turn off after 15 minutes-all that is needed is a simple modification of the trigger circuit. Then, the time when the alarm when the timer starts to run is activated. The alarm will stop 15 minutes later-regardless of the cycle status. Due to manufacturing tolerances-the exact length of any delay depends on the characteristics of the components in the actual circuit you are using. However, by changing the values ​​of R3 and R6 and R9, you can adjust the entry and exit times to meet your requirements. Increased value increases time-and vice versa. Welcome to reprint, this article comes from the electronic enthusiast network (http: //) layout Bill of materials
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